HORIZONTAL-TO-VERTICAL COMPONENT RATIOS FOR EARTHQUAKE GROUND MOTIONS RECORDED

ON HARD ROCK SITES IN CANADA

By: Jamila A. Siddiqi, M.Sc. Supervisor: Dr. Gail M. Atkinson

A thesis subrnitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the

degree of Master of Science

Department of Earth Sciences Carleton University

Ottawa, Ontario, Canada March, 2000

O Copyright 2000, Carleton University

National Library W B ofCam* Bibliothèque nationale du Canada

AcQUisWns and Acquisitions et BiMmgisphE Sewvices services bibliographiques

The author has granted a non- exclusive licence aiiowing the National Library of Canada to reproduce, loan, distriiute or sel1 copies of this thesis in microforni, paper or electronic formats.

The author retains ownership of the copyright in this thesis. Neither the thesis nor substantial extracts fkom it may be printed or oîhenuise reproduced without the author's permission.

L'auteur a accordé une licence non exclusive permettant à la Bibliothèque nationale du Canada de reproduire, prêter, distribuer ou vendre des copies de cette thèse sous la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique.

L'auteur conserve la propriété du droit d'auteur qui protège cette thèse. Ni la thèse ni des extraits substantiels de celle-ci ne doivent être imprimés ou autrement reproduits sans son autorisation.

ABSTRACT

In seismic hazard assessment, site response is one of the most important factors

to be determined. In this study, we explore site response for hard rock sites in

different parts of Canada. Rock response is an important component of the

overall response of any site, and important in the interpretation of seismograms

to separate source, path and site effects. The technique used for this purpose

was originally proposed by Nakamura (1 989) and further extended by Lermo and

Chavez-Garcia (1 993). According to this method, amplification can be inferred by

taking the horizontal-to-vertical component Fourier spectral ratio (HN) of the site.

The hypothesis of this technique is that for a soft layer overlying a half space, the

soft layer will amplify the horizontal component of ground motion, while

amplification effects on the vertical component are small enough to be neglected.

The HN method was applied to an earthquake database compiled from the

records of 32, three-component, Canadian National Seismograph Network

(CNSN) stations. These stations are located on rock outcrops. A total of 61

earthquakes of magnitude 4 - 6 from 1993 - 1996, and 363 earthquakes of

magnitude 2 2 from 1998 - 1999 were used in this study. Nakamura's method

was applied to the strong S-wave part extracted from the seismograms.

Assuming the computed HN ratios to be a measure of site amplification,

amplification factors for rock sites in the eastem, middle, and western parts of

Canada were deterrnined. The results at frequencies of 1-hz and 5-hz are

iii

compared. For eastem Canada, average amplification at 1 -hz is 1.1 and at 5-hz,

it is 1 -5, For midocanada, the average amplification at 1 -hz is 1.2 and at 5-hz, it is

also 1.2 (this value excludes the mean HN ratio values for one station to avoid

bias due to a high site response). For SW-Canada, amplification at 1-hz is 1.1

and at 5-hz, it is 1.2. For NW-Canada, amplification at 1-hz is 1.1 and at 5-hz, it

is 1.5. Thus the average HN for typical rock sites is 1.1 +_ 0.1 at 7-hz, and

between 1.2 - 1.5 at 5-hz for the whole country, regardless of geographic

location. We generally conclude that the effect of amplification tends to grow

with increasing frequency, consistent with what would be expected from a

decrease in shear-wave velocity as the seismic waves approach the surface. The

midocanada sites have the lowest inferred site amplification, consistent with

competent hard-rock site conditions with high near-surface shear-wave

velocities. The interpretation of the WV ratio as a measure of site response is

consistent with the general geological conditions of the recording sites; the 5-hz

H N ratio appean to be correlated with local geological conditions.

ACKNOWLEDGEMENTS

The completion of this thesis was made possible by the help and support of a lot

of people and in this section I would like to express my gratitude to al1 of them. At

the top of this list is my supervisor, Dr. Gail Atkinson for her never ending

patience and guidance. She has inspired me as a teacher and as a professional.

I also appreciate the resources and guidance provided to me by the people at

GSC, especially Bill Shannon, during the data collection phase of rny work. And, I

can not possibly thank enough my teachers and colleagues in the department,

particularly the Graduate Supervisor Dr. Sharon Carr and my colleagues Eleanor

Sonley and Dariush Motazedian. I also owe thanks to people at Geography

department, especially my teacher Dan Patterson, for helping me make and

produce maps using their lab facilities.

My final note of appreciation is for my family and my friends. My husband Asirn

Siddiqi and my daughter Mariam were with me during the ups and downs of this

project. I am also thankful to my sister Dr. Shafqat Shehzad who came to help

me by taking care of my daughter while I worked, and my parents for their

constant moral support.

TABLE OF CONTENTS

Title page

Acceptance fom

Abstract

Acknowledgements

Table of Contents

List of Tab tes

List of Figures

CHAPTER 1

1.1 Synopsis

1.2 Organization Of Work

1.3 Findings Of Study

i

ii

iii

v

vi

X

INTRODUCTION

1

2

3

CHAPTER 2 REVIEW OF LITERATURE

2.1 Introduction 4

2.2 Ovewiew of Seismic Wave Propagation 4

2.2.1 Shear-Waves 5

2.2.2 Rayleigh Waves 6

2.3 Overview of Site Amplification 7

2.3.1 Effect of lmpedance Changes

2.3.2 Resonance Effects

2.3.3 Hard Rock Site Effects

Techniques For Estimating Dynamic Characteristics

Nakamura's Technique

2.5.1 Verification Of The Method

General Application Of Nakamura's Technique To S-W ave

Amplification

Uses Of H N Technique

Comparison With Other Techniques

Stability Tests

Site Amplification Maps

Influence Of Diffetent Parameters On H/V Ratio

Limitations Of Nakamura's Technique

Surnmaty of Reviewed Articles

CHAPTER 3

3.1 Introduction

3.2 Recording Stations

3.3 Processing for Events From 1993 - 1996

3.3.1 Data Selection

3.3.2 Oata CaHection

3.3.3 Data Processing

DATABASE AND PROCESSING

34

35

36

36

38

39

vii

3.3.4 The Output

3.4 Processing for Eventç From 1998 - 1999

CHAPTER 4 H/V RATIO RESULTS

Introduction

H N Ratio Calculation

4.2.1 Ratio Calculation for 1993 - 1996 Data

4.2.2 Ratio Calculation for t 998 - 1999 Data

Calculation of Mean HN

HN Results

CHAPTER 5 CORRELATION OF WV RATIOS WITH GEOLOGY

5, t introduction 7 2

5.2 General Geology 73

5.2.1 Main Geological Ragions 73

5.2.2 Surface Materials 77

5.3 Analysis Of H N In Light Of Geology Of Recording Station 80

5.3.1 HN Ratios at 1 HZ 81

5.3.2 WV Ratios at 5 HZ 84

CHAPTER 6

6.1 lntroduction

6.2 Seismological Properties

CONCLUSIONS

93

93

6.3 Results of The Study

6.4 Future Prospects and Summary of Conclusions

Appendix

References

LlST OF TABLES

Table 3.1

Table 3.2

Table 3.3

Table 4.1

Table 5.1

Table 5.2

Table 5.3

Table 5.4

Table 5.5

Table 5.6

Table 5.7

Table 5.8

Table 6.1

Table 6.2

Table 6.3

Table 6.4

Table 6.5

Table 6.6

Table 6.7

List of Recording Stations 35

List of Events from 1 993 - 1 996 37

List of Events from 1998 - 1999 42

Calculation of H N Ratio 52

The Four Main Geological Units of Canada 74

Reclassification Scheme for The Surficial Materials of Canada 78

W for 1 -hz, HN < 1 (class A-1 a) 81

H N for 1 -hz, H N = 1 - 1.2 (class A 4 b) 81

HN for 1 -hz, W > 1.3 (class A-1 c) 82

H N for 5-hz, WV < 1.2 (class A-5a) 84

H N for 5hz, HA/ = 1.2 - 1.4 (class A-5b) 84

H N for 5-hz, H N > 1.4 (class A-Sc) 85

Site Effect Studies for Western Canada 94

Site Effect Studies for Eastern Canada 95

Amplification Factors for SW-Canada 96

Am piification Factors for NW-Canada 96

Amplification Factors for Eastern Canada 97

Amplification Factors for Mideanada 98

Cornpaison of mean HN, Standard Deviation and

90% Confidence Intenial at 1 -hz and 5-hz

LIST OF FIGURES

Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 5.1

Figure 5.2

Figure 5.3

Figure 5.4

Figure 5.5

Figure 5.6

Figure 5.7

Mean H N Ratios, Standard Deviation, 90% Confidence

lnterval For Eastern Stations

Mean H N Ratios, Standard Deviation, 90% Confidence

lnterval For Mid-Canada Stations

Mean H N Ratios, Standard Deviation, 90% Confidence

lnterval For SW-Canada Stations

Mean H N Ratios, Standard Deviation, 90% Confidence

Interval For NW-Canada Stations

Main Geological Regions of Canada

Earthquakes and Recording Stations With Surface Geology

Surface Geology and Mean H N Values for NW-Canada

Surface Geology and Mean HN Values for SW-Canada

Surface Geology and Mean H N Values for mid-Canada

Surface Geology and Mean WV Values for Eastern Canada

Surface Geology Map for Charlevoix Area

CHAPTER 1

INTRODUCTION

1.1 SYNOPSIS

In seismology, it is well known that soi1 deposits amplify ground motion. The

amount of amplification depends on several factors such as compaction, age,

layer thickness etc. These factors influence the shear-wave velocity, density and

damping characteristics of the soil. It is often assumed that hard rock materials

do not amplify ground motion. However, the results of previous studies indicate

that rock sites may also have significant amplification due to their shear-wave

velocity gradient. In this study, we investigate site response associated with hard

rock seismograph sites in Canada, as inferred from the ratio of the horizontal-to-

vertical component of the Fourier spectrum of ground motions. For this purpose,

an earthquake database was compiled based on the seismograph records

obtained from the Geological Survey of Canada (GSC). In total, 61 earthquakes

of magnitude 4 to 6 from 1993 - 1996 and 363 earthquakes of magnitude 5 2

from 1998 - 1999 were analyzed. 32 broadband, three-component Canadian

National Seismographic Network (CNSN) seismograph stations recorded these

events. The strong S-wave part of the seismograms was windowed from the time

series of each component of each record. The Fourier spectrum was calculated,

and the ratio of the horizontal to veitical component detennined as a function of

frequency (HN). According tu Nakamura (1989) and othen, the H N ratio is a

measure of site amplification. The WV ratios detemined by this study were

correlated with the general geological conditions of the sites and compared with

the findings of previous studies.

1.2 ORGANIZATION OF WORK

The thesis is organized in six chapters. Chapter 1 presents a brief introduction to

the work done in the study, an outline of how the work is organized, and an

overview of the findings of the study.

Chapter 2 gives the requisite theoretical background of S-waves and Rayleigh

waves and their role in the phenornenon of site amplification. An outline of the

technique applied in this study is given along with a review of previous studies

utilizing this method.

Chapter 3 describes the database used in the study and the data processing

procedures. The time series of selected events were processed in a software

package (SAC: Seismic Analysis Code) to window the S-wave and a noise

sample of the seismograms. These windows were then transformed to the

frequency domain by Fast Fourier transfomi. The values were sampled at 24

frequency values, spaced at interval of 0.1 log frequency units (smoothed within

the frequency bins). Data in this fom were then used to calculate the horizontal

to vertical component ratio (WV) as a function of frequency.

Chapter 4 presents the computed W ratios. The procedure of calculating the

ratios is also discussed. The ratios were calculated partly by using spreadsheet

software and partly by FORTRAN programs. Once the ratios were obtained, their

mean, standard deviation and 90% confidence intervals were also calculated.

The results are displayed in graphical form and tabulated in the Appendix.

Chapter 5 discusses the regional geological units and the local surficial materials

of Canada with focus on the locations of the seismograph sites. These are

presented in the form of tables and maps. WV ratios were then examined for a

possible correlation with the local geology. And, in Chapter 6, we present the

conclusions and discuss the WV results of this study in cornparison with those of

previous studies.

1.3 FlNDlNGS OF THE STUDY

The findings of this study suggest that although the WV ratios are not high for the

hard rock sites, they are often significantly greater than unity. This suggests

significant site amplification. On average, the highest inferred amplification is a

factor of 1.5 at 5-hz, for rock sites in northwestem Canada. The average HN for

typical rock site is 1.1 I 0.1 at 1 -hz and between 1.2 - 1.5 at 5-hz for the whole

country. These results are generally consistent with the findings of limited

previous studies. A correlation of the computed H N ratios with the local geology

shows that at higher frequencies (5-hz), the H N is influenced by the local

geological conditions.

CHA PTER 2

2.1 INTRODUCTION

This chapter reviews the literature conceming the response of surficial materials

to seismic excitation, focusing on those studies that are based on the use of the

horizontal-to-vertical component spectral ratio technique, as proposed by

Nakamura (1989). 1 first outline underlying theory related to seismic waves and

the phenornenon of arnplif ication. Then details of Nakamura's technique are

given, and alternative site response estimation techniques and their advantages

and disadvantages for studying seismic response are explored. However, the

main focus of the chapter is on Nakamura's work. Nakamura's technique uses

the ratio of the horizontal-to-vertical component of ground motion to calculate the

site transfer function; the advantage of this technique is that it is simple to apply,

and does not require a "reference" station. I describe how Nakamura's technique

has been tested or used in several empirical studies, and discuss the limitations

and uses of this technique.

2.2 OVERVIEW OF SEISMIC WAVE PROPAGATION

In considering the amplification of seismic waves by near-surface materials we

are concemed with both body waves that travel inside the earth, and surface

waves that propagate along the surface of the earth. Body waves include

compressional (P-waves) and shear (S-waves), although it is the S-waves that

are of most interest because their amplitudes are generally much higher than P-

wave amplitudes. Surface waves include Love waves and Rayleigh waves. At

large distances surface waves carry the largest amplitudes. Surface waves arise

as a consequence of the free surface of the Earth and are also known as

bounded or guided waves. On the other hand, body waves propagate in all

directions from the source. (Kulhanek, 1990). The properties of S-waves and

Rayleigh waves are of most interest to this study and are outlined below.

2.2.1 SHEAR WAVES

Shear waves (S-waves) are also known as secondaiy waves because they are

the second phase recorded on regional seismograms, after the arriva1 of the

faster P-waves. The particles in the path of S-waves move perpendicular to the

direction of wave propagation. S-waves do not pass through liquids because

liquids do not transmit shear stress. S-waves travel with a velocity P, given by

P = (ri/p)0*5 , where

p = Shear modulus (which is one of the two Lame's constants; this is the

stress- strain ratio for simple shear)

p = Density of the medium.

S-wave motion can be resolved into components parallel and perpendicular to

the surface of the ground. These are SH and SV waves respectively. S-waves

that involve motion in only one plane are known as 'plane polarized' waves.

(Sheriff and Geldart, 1995). Love waves are a special type of shear waves that

propagate along the free surface of the Earth.

2.2.2 RAYLEIGH WAVES

Surface waves, inciuding Love and Rayleigh waves, propagate along the free

surface of the Earth; the amplitude of surface waves is largest at or near the

surface and decreases rapidly with depth. Shallow eaithquakes generate large

surface waves but for deeper shocks (h>100 km) surface waves become

insignificant. This fact helps distinguish shallow from deep shocks. (Kulhanek.

1990)

In Rayleigh waves, sometimes refened to as "ground roll", the particle motion

near the surface is elliptical and retrograde. This means that the particle moves

opposite to the direction of propagation at the top of its elliptical path. The particle

motion is largely in the vertical plane. Rayleigh waves are low-velocity, low-

frequency waves with a broad range of wavelengths. Since the velocity of

Rayleigh waves depends on the elastic properties of the medium to a depth of

one wavelength, the variability of elastic constants changes the velocity of

Rayleigh waves. (Sheriff and Geldart, 1995). It also follows that the velocity

varies with frequency (or wavelength). For wavelengths that are very short

compared with the layer thickness the propagation speed of Rayleigh waves is

about nine-tenths of the shear velocity in the material comprising the surface

layer. For very long wavelengths, relative to the thickness of a surficial layer, the

Rayleigh-wave speed is nine-tenths the shear velocity in the substratum material,

since the effect of the surface layer is negligible when most of the wave travels in

the zone below it. For intermediate wavelengths the velocity falls between these

extremes. This variation of velocity with frequency or wavelength is known as

'dispersion'. (Dobrin, 1984); it results in a signal that grows in duration and

separates in frequency as distance increases. Rayleigh waves are of particular

importance in the formulation of Nakamura's technique, as will be discussed in

the next sections.

2.3 OVERVIEW OF SITE AMPLIFICATION

When an earthquake occurs, strain energy is released that spreads through the

surrounding crust in the form of seismic waves. During an earthquake, different

crustal structures will exhibit different seismic response characteristics. Similarly.

a crustal structure may behave differently for different earthquakes, introducing

variability in the site response characteristics. The dynamic characteristics of the

motion at an obsenration point on the earth's surface can be written in the

frequency domain as follows:

0 ( f ) = F ( f ) . T ( t ) . S ( 1 )

O ( 1 ) = Observed Fourier spectrum of motion at a point on Earth's surface (as a

function of frequency.)

F ( f ) = Spectrum of radiation from the focal region, or the source effect.

T ( f ) = Transmission characteristics of wave motion propagation through the

crustal path, or the path effect.

S ( f ) = Dynamic characteristics of near surface layers beneath the observation

point, or the site effect. (Nakamura, 1989).

It is generally obsewed that the effect of surface layers, S ( 1 ), is the most

crucial among the three factors influencing the recorded radiations. Therefore, in

seismic hazard analysis, site amplification is one of the key factors that

determine the amplitude of expected ground motions. Thus 1 is important to

understand why this phenomenon occurs. The amplification of seismic waves

may be caused by impedance changes due to a velocity gradient, resonance

effects due to a soft layer, and effects due to two-dimensional or three-

dimensional geometric effects.

2.3.1 EFFECTS OF IMPEDANCE CHANGES

Consider two horizontal layers, where the velocity of underlying layer 2 is greater

than the velocity of surficial layer 1. As a seismic wave travels towards the

surface from layer 2 to layer 1, the energy E per unit area carried by a wave of

single wavelength is given by:

E = ~ ? P v ~ A ~ , where:

p = density, V = velocity, f = frequency, A = amplitude.

Assuming that al1 or nearly al1 energy is transmitted, then the energy in layer 1

must be equal to that in layer 2. By equating the expressions for energy in the

layers, we see that:

AdA2 = (pz VZ / PI VI)'.~, where:

Al is the wave amplitude in layer 1, A2 is the wave amplitude in layer 2, etc.

In this relation, the product of density and veiocity (p V) is known as acoustic

impedance. If pz V2 > pl VI, the height of the wave will be arnplified in layer 1,

relative to its incaming amplitude from layer 2. (Atkinson, 1999)

2.3.2 RESONANCE EFFECTS

Resonance effects are caused by a discontinuity in the medium properties, which

leads to trapped waves with multiple reflections within the layer. When the

reflected waves have constructive interference, the phenornenon of resonance

occurs. Resonance effects depend on the thickness and elastic properties of the

trapping layer. The phase shift required for resonance (assuming a 180' phase

shift at the boundary) is given by:

fn=(2n-1)V/4H.

Where n = 1 , 2,.. V= velocity of S-wave, H = thickness of the layer.

For n = 1, the fundamental resonance frequency is obtained:

f l =V/4H.

If the above equation is re-arranged to obtain an expression for thickness, we

see that:

H = V / 4 f

Since the wavelength, h = V I f, the above expression can be rewritten to produce

the well known "quarter-wavelength rule":

H = U 4

Hence, the frequency of the resonant peak can be used to find the thickness of

the layer (if the velocity is known). The resonant amplification is given by the ratio

of acoustic impedance in the first and the second layer: pz V p / pl VI. Note that

the amplification due to resonance is greater than that due to a simple impe-

dance effect. (Atkinson, 1 999)

2.3.3 HARO ROCK SITE EFFECTS

It is well known that soi1 sites can strongly influence seismic signals, while it is

often believed that hard rock sites have negligible site effects. However, rock

sites may also arnplify incoming waves, due to either impedance or topographic

effects. Tucker et al (1984) conducted a study, which showed that there are

significant topographic rock site effects. Basernent rock outcrops on a ridge can

amplify motions by a factor of eight over a narrow frequency band. Rock sites on

topographic features affect frequencies inversely proportional to the dimension of

the feature. Geli et al (1988) surveyed the effect of topography on seismic

motion. They conclude that amplification is greater on hilltops with respect to the

base. This phenornenon occurs at frequencies corresponding to wavelengths

equal to the mountain width. The sides of the hills experience cornplex

amplification and de-amplification patterns particularly in the upper parts of the

hill. Thus for rock sites. topographic amplification effects may be significant.

There rnay also be rock amplification due to near-surface weathering, as this

results in acoustic impedance differences.

2.4 TECHNIQUES FOR ESTlMATlNG DYNAMIC SITE CHARACTERISTICS

In order to explore the dynamic excitation characteristics of near-surface

materials, various estimation techniques have been used. Borehole methods

and micro-tremor methods are commonly applied. A brief description is given

below.

Borehole Methods: Borehole methods have been used to measure directly the

ground motion amplitudes at the surface versus those at depth. This method can

be very accurate and is very expensive because drillholes must be made, often

to large depths (tens of meten), and borehole seismometers must be placed in

the boreholes. Hence, borehole methods are used only for special studies where

a significant budget is available.

Micro-tremor Methods: Micro-tremors are small tremors of short period caused

by: (i) natural sources (e.g. storms and seas), and (ii) artificial sources. Waves

from sea sources are long period tremon (2-3 seconds), while those from

artificial sources are usually short period motions. (0.05 to 1 second) (Nakamura,

1 989).

The method of using micro-tremor measurements to detenine site response is

very useful because it is simple and economical. The micro-tremors can be

analyzed to obtain site amplification using either a "reference sitey' technique or

"Nakamura's technique". The "reference site" technique involves making

recordings on both a soi1 site of interest. and a nearby "reference" rock outcrop.

Amplification is then obtained as the ratio of the soi1 to the reference rock motion.

The problem with this method is the identification of a common wave train for the

two stations. (Lemo & Chavez-Garcia, 1994). In this approach, the effect of the

particular source of micro-tremors should be minimized and the measurements

should be taken during a relatively quiet time like midnight to avoid background

micro-tremor levels. These constraints remove the advantage of taking the

measurements readily. (Nakamura, 1 989)

Nakamura (1 989) proposed a new micro-tremor method for amplification studies,

which avoids the constraints of the reference site approach. The dynamic

characteristics of surface layers are estimated by measuring solely the micro-

tremor at the surface of the soi1 layer. A stable estimation of predominant

frequency and amplification factor can be made regardless of the excitation

source, Nakamura's method is based on the resemblance of the transfer function

for the horizontal motion of surface layers to the spectral ratio of the horizontal-

to-vertical component motion. The advantage of Nakamura's technique is that it

works well even in the presence of artificial tremors and is not affected by micro-

tremor noise. There is no need for a reference site.

2.5 NAKAMURA'S TECHNIQUE

Nakamura made micro-tremor observations for two sites continuously for thirty

hours. His obseivations at one of the sites, Kamonomiya, showed that the

dominant vibration frequency of the surface layers was about 1.5-hz as observed

during quiet time periods. For the other obsewation site, Tabata, he found that 2

to 3-hz and 4 to 8-hz frequencies were dominant. However, it was determined

that a train induced the 4-hz tremors. This source caused a considerable change

in the micro-tremor observations, especially in the vertical component.

Frequencies of 2 to 3-hz prevailed at Tabata during quiet time spans. Hence,

fluctuations in the prevailing observed frequency of micro-tremon may be

caused by a strong effect of aitificial tremors in the surrounding areas. Artificial

tremor sources have mostly prevailing vertical motions as they induce Rayleigh

waves. Rayleigh waves may therefore be treated as noise in micro-tremor

surveys.

Nakamura's concept of using micro-tremor observations to detemine the

response characteristics of surficial materials is based on the following

assumptions:

Micro-tremors consist of various wave motions.

The ratio of the horizontal component to the vertical component spectrum of

earthquake motions (= AH / AV) is related to soi1 conditions.

AH / AV is close to 1 for hard rock (having high shear wave velocity).

Horizontal and vertical tremor motions are similar to each other as input at the

base of the surficial layer and are amplified by soft surface layers on hard

su bstrate.

Based on these assumpüons, Nakamura (1989) develops a new transfer function

estimation method to deterrnine the horizontal-component amplification of

surface layers. The transfer function ST of sutface layen, for horizontal motions,

is generally defined as

ST = Sns l SHB , Where

SHs . Horizontal tremor spectrum on the surface. SHs is readily affected by

surface waves. Since artificial noise sources mostly propagate as Rayleigh

waves, SHS of micro-tremors may possibly be affected by Rayleigh waves.

Sne. Horizontal tremor spectrum incident at the substrate (base of surficial layer)

The effect of surface layer on vertical tremors, Es, can be written:

ES = Svs 1 Sve

Here, Es primarily represents the contribution of Rayleigh waves to the vertical

tremor motions, as there is generally no significant amplification of motion in the

vertical cornponent by low-velocity layers near the surface (because the

refraction of the rays towards the vertical reduces the verticalçornponent shear

amplitudes, counterbalancing the irnpedance amplification effects). If there is no

Rayleigh wave contribution, then, Es = 1. If Es > 1, it indicates a significant

Rayleigh wave effect. Assuming that the relative effect of Rayleigh waves (at the

surface versus at the base) is equal on vertical and horizontal cornponents, a

more diable transfer function for the horizontal motions, that removes the

spurious Rayleigh waves contributions from artificial sources, can be written as:

Sm =SrlEs=(SnslSne). (Sve/ Svo)=RslRe

Here Rs = Sns 1 Svs

And Re = SHBl Sve

Nakamura obtains Rs by dividing the horizontal tremor spectrum, measured at

the surface, SHs, by the vertical spectrum Svs, also measured at the surface.

Theoretically and experimentally

Sne = Sv= so Re = 1 and thus

Sn = Rs = S n g l S v s

This relation implies that the transfer function of surface layer may be estimated

from surface measurements of the tremors only, at a single station. Put sirnply,

the vertical tremor on the surface retains the characteristics of the horizontal

tremor input at the base of the substrate, and hence substitutes for the latter.

Nakamura's method includes a correction through Rs to eliminate the effects of

Rayleigh wave contributions. Howevet, results show that the accuracy of the

amplification estimates is reduced when there exists a noise tremor whose

frequency matches the prevailing frequency in the estimated transfer function.

(Nakamura, 1989)

2.5.1 VERIFICATION OF THE METHOD

Nakamura verified the micro-tremor site response results at the two observation

points at Kamonomiya and Tabata. At Kamonomiya, he computed the transfer

function Sn from seismic obseivations using the reference site technique, and

compared the results with the average of Rs = Sns/ Svs . His results showed that

Rs is similar to Sn in terms of the peak frequency, amplification and shape. At

Tabata, Sm and Rs were estimated from simultaneous observations of micro-

trernors on the surface and at a point 25 rneters below the surface, over a 24-

hour period. The ratio of the surface-to-downhole observations was used to

compute Sm while Rs was computed from the surface obsewations oniy. The

values of Sm and Rs were shown to be roughly similar. Nakamura also

cornpared Rs and Sr at Mexico City using the recordings of strong earthquake

motions to compute ST using the reference site approach. Rs was then obtained

by micro-tremor observations. He found that the maximum amplification of peak

ground velocity due to the soi1 layer could be estimated by using the maximum

acceleration ratio of horizontal and vertical tremors on the surface, although there

was considerable variability. In al1 cases, however, Rs and ST were highly

correlated with each other, implying that Rs is a good estimator of the transfer

function.

2.6 GENERAL APPLICATION OF NAKAMURA'S TECHNIQUE

10 S-WAVE AMPLIFICATION

Nakamura's technique was developed for micro-tremor studies of site

amplification. Lemo and Chavez-Garcia (1 993) extended this technique for the

strong S-wave part of earoiquake seisrnograms. To explain why Nakamura's

technique should be applicable to the S-waves, Lerrno and Chavez-Garcia

(1993) follow two lines of argument. They observe that in Mexico City, the

amplification factors due to a thin soft layer are very high (amplification of a factor

of 50 was obseived in the 1985 Michoacan earthquake). For the vertical

component however, the amplification facton are small enough to be neglected

and this is invariant to the soi1 condition and the magnitude of the earthquake.

Therefore, the vertical component can be used as an estirnate of the ground

motion incident to the surficial layer. Their second argument is based on

numerical modelling. In this model, they assume that site effects are caused by a

single layer over half space, and the excitation is due to plane S-waves. The

parameters of this model are incidence angle and the mechanical properties of

the layers. They compute the theoretical transfer functions of the model and

obseive that for the horizontal component, the amplitude of the resonant peak

varies (by a factor larger than 2) as a function of incidence angle. For the vertical

component, this variation is srnall and is less than a factor of 2. They also

computed the transfer function of the model using Nakamura's method. They

found that for all angles of incidence, resonance frequencies were identified well

by Nakamura's ratio. For incidence angles of 50' and greater, the resonance

frequency and also the amplification values at the first resonance frequency

agreed well with the standard spectral ratios. (Lemo and Chavez-Garcia, 1993).

In another study by Lachet and Bard, (1994), the authors notice that the H N ratio

is a stable site characteristic for body waves. This result is verified by

experiments done by researchers such as Lemo and Chavez-Garcia. Therefore,

the H N ratio can be used as an estimate of site amplification for weak or strong

motion recordings.

2.7 USES OF HN TECHNIQUE

Since Nakamura originally proposed the technique, several investigators have

applied this technique to estimate amplification based on the WV ratio, using

earthquake databases in different parts of the world. An overview of pertinent

results is given here:

For cities with different geological and tectonic settings, the site response

estimates obtained with the HN method were cornpared with standard

spectral ratio techniques based on a reference rock site, and found to be very

similar. (Leno 8 Chavez-Garcia, 1993).

If site effects are caused by simple geology, it is possible to estimate the

dominant period and local amplification factor using records at only one

station, based on HN. The method gives a good estimate of the frequency

and amplitude of the first resonant mode, though the higher modes do not

appear. (Leno & Chavez-Garcia, 1 993).

The rnethod is useful for site effect evaluation in urban areas. Knowledge of

the resonance frequency of the soi1 is an effective tool in detemining the

kinds of buildings most susceptible to damage. (Lachet & Bard, 1994)

Micro-trernor measurements can complernent other site effect studies. For

example, in regions of low seisrnicity, site amplifications can be spatially

interpolated with micro-tremor data. (Lermo & Chavez-Garcia, 1 994). In one

study by Duval et al (1995), W curves were spatially interpolated ta obtain

mami of soectral site effect. The results were in accordance with the

geological data. Also, the highest computed amplifications coincided with

areas known to experience strong site effects during earthquakes.

Since micro-tremor measurements are simple and inexpensive to obtain, they

can be used in microzonation techniques, especially in urban areas. (Teves-

Costa et al, 1995). An example of this is the study undertaken by Bour et al

(1998) in which H N spectral ratios were used to establish maps to

characterize the site amplifications for the Rhone Delta region (France).

Resonance frequency maps and maps of amplification level were used for the

seismic microzonation for the whole reg ion.

Field and Jacob (1995) observe the H N method of assessing site response is

very useful for hazard assessrnent in regions that lack adequate reference

sites.

2.8 COMPARISON WlTH OTHER TECHNIQUES:

In this section, Nakamura's (1989) technique will be compared to the other widely

used techniques to estimate the site response. Broadly, these include the

popular spectral ratio technique (based on a reference rock site), and numerical

simulation techniques.

The spectral ratio technique is among the widely used techniques for the

estimation of site effects in regions of moderate to high seismicity. It consists of

recording several earthquakes in an array of stations. One station serves as the

reference station and is located on hard rock, away from the source of site

effects. The S-wave signal from earthquakes is used to estimate the site effects

of soi1 stations relative to the reference station. Lermo and Chavez-Garcia

(1993) have compared the results of Nakamura's technique with the results

obtained using the spectral ratio technique. For the spectral ratio technique, they

observe that the technique has some important limitations to it. For example, the

nearby reference station rnay not record al1 of the events recorded by the soft soi1

(due to lower signal amplitudes). This introduces the constraint of long periods of

observation, so that sufficient events are recorded simultaneously on both sites.

In some areas, it might be difficuit or impossible to find a nearby reference station

on rock. Also, in the case of spectral ratio technique, the reference station is

located on a rock site, which might itself have a significant site response. In

Nakamura's technique, by contrast, we do not need a reference station, thereby

eliminating many of these limitations.

In a study by Field and Jacob (1995), the modified H N technique (as proposed

by Lermo and Chavez-Garcia, 1993) was applied to the shear-wave part of the

aftershock records of the California 1989 Loma Prieta earthquake. From the H N

ratio technique, they were able to reproduce fundamental and higher mode

resonant peaks for the sites under study. They found, however, that the

amplitudes obtained using the WV ratio technique were underpredicted as

compared to the spectral ratio estimates. In the case of the study by Lermo &

Chavez Garcia (1993), they were able to reveal only the fundamental resonant

frequency. Unlike the results of Field and Jacob (1995), the HN amplification

estimate at the fundamental frequency was in good agreement with the

am plif ication obtained from the spectral ratio method. Finally, Lermo & C havez-

Garcia found less variability among the H N ratios compared to spectral ratios. By

contrast, Field and Jacob found the unceitainty level to be the same for the two

techniques. A study by Bonilla et al (1997) finds that HN ratio technique obtains

the same predominant peaks as the direct spectral ratio method, but the

amplification level obtained is different for the two techniques.

Nakamura's technique has also been compared with the results of numerical

simulation techniques and theoretical models. For example, Tavez-Costa et al

(1996) made a cornparison with 2D theoretical results for a vertically incident SV-

wave. Fourier transforrn functions for different points on the basin under study

were obtained. Comparing the theoretical H N ratios and the Fourier transfer

functions, three out of five stations show agreement between the dominant

frequency and the resonance frequency. For the other two stations, the authors

concluded that they might not have been properly modelled by the synthetic data.

Bour et al (1998) compared the results of their study, which utilised Nakamura's

technique, to the solutions of one-dimensional numerical simulation models of

site response (based on a popular engineering program called SHAKE91). The

simulation model cornputes the response of horizontally layered soils under

seismic excitation, assuming equivalent linear soi1 behaviour. Using geotechnical

and drilling data. they constructed models of the soi1 columns for several

industrial sites. Then these soi1 colurnns were used to calculate transfer function

using the prograrn SHAKE91. A comparison of results reveals good overall

agreement between the transfer functions obtained by the two methodologies.

However, the amplification suggested by the H N ratio is higher than that

obtained by nume rical modelling .

2.9 STABILITY TESTS

Tavez-Costa et al (1996) examined time variant characteristics of the micro-

tremor amplitudes and the stability of HN spectral ratios over repeated

observations. In their study, micro-tremors were continuously recorded at a rock

site. Their results show that the predorninant frequency of the ratio remains

stable over repeated observations despite the amplitude fluctuations presented

for each cornponent. The authors also applied this technique to thick and thin

alluvial deposits and compared the results with numerical simulations. Their

results indicate that the observed predominant frequency is, as expected, based

on the thickness of the alluviurn deposits, for thin alluvium deposits. For thick

alluvial deposits, one deposit showed predominant frequencies that agreed with

theoretical results. For another thick basin, however, the H N ratios did not

present a peak so clearly. The authors concluded that the reason for this could

be that the impedance contrast was not so strong. Overall. the evaluated

predominant frequencies correlated well with the depths of alluvial deposits.

Theodulidis et al (1996) checked the stability of the H N spectral ratio at different

depths in the Garner Valley Downhole array in Southern California. They found

that the stability of these ratios at each individual depth (as deduced from the

standard deviation values) was remarkable. However, their shape drastically

changed from the surface to a depth of 220 meten, indicating the influence of

depth and site geology. They compared the mean spectral ratio of surface to

deep sites with the mean H N ratio on the surface. Their study found a similarity

in the shape of spectral ratio and H N ratio curves for frequencies below 10-hz

and above 13-hz. However, HN ratio exhibits a simpler shape than the actual

spectral ratio of surface to deep motions. Theodulidis et al. (1996) also

cornpared experimental to synthetic ground motion data for the ratio of surface to

deep motions. The H N spectral ratios of the experirnental data showed 2 - 4

times lower amplitude than the corresponding synthetic ones. This could be

because in the synthetic data, scattered waves are absent. Also, for the H N

spectral ratio, the amplitudes are lower for the experimental data implying an

enrichment of the vertical component due to the presence of scattered waves.

The authors also concluded that the focal mechanism radiation pattern seriously

affects the theoretical H N ratio amplitude, but the shape of the H N ratio curve

remains the same for different focal mechanisms. Variations in the regional

quality factor (Q) do not change the shape and amplitude of H N ratio.

Duval et al (1 995) investigated the stability of the HN ratios, using a micro-tremor

data set obtained for Niceport, France. They found that HN ratios inferred from

recorded micro-tremor spectra were stable, even between day and night, in

cornparison to the source spectra (which varied greatly). At sediment sites, H N

ratios from micro-tremors f o n peaks centred at a well-defined frequency. They

also studied velocimeter-recording data at 10-meter distance spacing. For

velocimeters placed in the same geological conditions, H N results were the

same.

2.10 SITE AMPLIFICATION MAPS

Duval et al (1995) produced amplification maps for the region of Nice, France,

based on micro-tremor observations. Recordings were obtained at a 50-meter

spacing for four days and nights. Data were processed and the values

interpreted for each site to obtain an H N ratio cuive in the frequency domain.

From these cuives, the maximum amplitude and its frequency were determined

for each site. These values were interpolated in space to produce site

amplification maps. The maps identified two zones where maximum amplification

values were high. These were the areas at the middle of the alluvial basin, and

on part of a lirnestone hill. The maximum amplification in the middle of the basin

occurred at a frequency between 0.5 - 2.0-hz. At higher frequencies, the

maximum leaves the deepest part of the fiIl to reach the edges of the valley.

Hence, by using the HN ratios, their spatial interpretations give valuable

indication about the distribution of the amplification peak. Bour et al (1998)

performed microzonation using Nakamura's method in the plain near Rhone

Delta in Southem France. In the Rhone Delta, there are several critical

installations in proximity to active faults. HN ratios were calculated from

recordings of background noise for a grid of sites. With these results, Bour et al

(1 998) produced maps to characterize amplification effects of the region. These

included a resonance frequency rnap and rnaps of amplification amplitudes as a

function of frequency range, leading to a seismic microzonation for the region.

2.1 1 INFLUENCE OF DIFFERENT PARAMETERS ON HN RATIO

Lachet and Bard (1994) studied the influence of different parameters on the H N

ratio. They carried out synthetic waveform calculations for fifteen soi1 profiles.

Noise was simulated as the signal produced at a single site by a set of superficial

sources distributed al1 around with random amplitude and time delay. Three

types of relations were explored. They included (i) variations in source

chacteristics (ii) influence of geological structure and (iii) varying incidence

angles. A bief description of the results of Lachet & Bard (1 994) is given below:

VARIATION OF SOURCE CHARACTERISTICS: Experiments were perfoned

using two different source types. The H N ratios obtained for different source

excitations al1 exhibit a peak whose position is constant regardless of the source

type and source function. This means that for randomly distributed surface

sources, the HN peak position is independent of the source characteristics.

Other calculations made for different geological structures with various sources

confirm the result.

INFLUENCE OF GEOLOGICAL STRUCTURE: Synthetic waveforms were gene-

rated for geological stnictures in three different regions: Ashigara Valley, Turkey

Flat and coastal site in SE France. The general shape of the H N ratios obtained

in these cases indicates that they present a clear peak at varying frequency.

Results obtained for different sites show a strong influence of geological

structures on the H N peak position. The resonance frequency as calculated for

vertically incident S-waves agrees well with the calculated H N peak frequency.

SV-WAVES WITH VARYING INCIDENCE ANGLE: A l -D Program was used to

compute the surface response to SV waves with incidence angle varying from 5'

to 89'. The results show that the H N ratios exhibit rather stable peaks, the first

of which corresponds to the fundamental resonance frequency. Theodulidis et al

(1 996) also found that the WV ratio due to incident P and SV plana waves exhibit

stable resonant peaks at vanous frequencies, whose positions are almost

independent of the incidence angle, although their absolute amplitudes Vary

significantly with incident angle.

2.1 2 LIMITATIONS OF NAKAMURA'S TECHNIQUE

Although Nakamura's technique has been successfully used as described above,

this section discusses the limitations of the technique and the possible solutions

to them.

1. THEORETICAL ASPECTS NEED FURTHER TESTING:

Guteirrez and Singh (1992) argue that while in some cases the micro-tremor

results agree reasonabiy well with those obtained during earthquakes, this is not

always the case. For example in Imperia1 Valley. California, site effects observed

from strong motion data were not satisfactorily reproduced from the analysis of

micro-trernor recordings. The origin and propagation of micro4 remors and their

reliability in shedding light on site affects still remain doubtful. They argue that a

general acceptance of the technique would require extensive testing against

amplification results obtained from earthquake records, which is a difficult

proposition in areas of low seismicity. In a recent study by Bour et al (1998), the

authors have pointed out that the physical phenomena underlying the method are

only partially understood.

2. W RATIOS SHOW ONLY THE FUNDAMENTAL RESONANCE:

Tavez-Costa et al (1 996) observe that when applied to micro-tremor recordings

for sedimentary sites with large impedance contrast with the underlying bedrock.

the W ratios exhibit a single peak, indicating only the fundamental frequency

and not the hamonics, or the whole frequency range over which the sedimentary

site amplifies motion. The amplitude of this peak does not seem well correlated

with the actual amplification of the S-wave amplitude. Lachet and Bard (1994)

observed that the peak in the HN ratio for micro-tremors might be related to the

polarisation curve of Rayleigh waves. These waves are polarized in both

horizontal and vertical directions. To test this, polarisation curves were computed

for a half space model, and for real sites. These curves were compared with H N

ratios calculated from a noise simulation. The results suggest that the H N peak

position in the noise simulation corresponds to the first peak in the polarisation

curves. This irnplies that the shape of the H N ratio from micro-tremor studies is

widely controlled by the fundamental Rayleigh wave.

3. AMPLITUDE OF THE HA# PEAK IS NOT A RELIABLE ESTIMATE OF

ACTUAL AMPLIFICATION:

Some researchers have observed that the amplitude of the HN peak does not

correlate well with actual amplification. (e.g, Lachet and Bard (1 994)).

Nakamura's technique suggests that it is possible to estimate the amplification of

seismic motion due to resonance of surface layers simply from the maximum

spectral amplitude of the H N ratio. Lachet and Bard test this hypothesis by

comparing the amplitude (An) of the H N peaks obtained from noise simulations

with the maximum amplitude of the transfer function for vertically incident S-

waves (A,). However, in the simulation results, they obtained a poor agreement

between the H N peak amplitude and the amplification for theoretical vertical S-

waves. Lachet and Bard (1994) further test the influence of Poisson's ratio on

the amplitude of the H N ratio. Their results show significant variations as a

function of V& ratio (which is related to Poisson's ratio).

Lachet and Bard (1994) also explore the possibility that results may be

influenced by the relative location of source and receivers. Therefore, they

investigated parameters like structure thickness, maximum source-receiver

distance and source depth, that might influence the excitation of surface waves.

Their results show that the greater is the source-receiver distance, the bigger is

the Rayleigh wave contribution, and thus the higher is the HN peak amplitude.

H N ratios obtained for varying source depths show that the W peak amplitude

remains nearly constant for different source depths. These results indicate that

the H N peak amplitude cannot be used in a straightforward way for amplitude

studies since it shows considerable vadability with respect to parameters such as

Poisson ratio in sedimentary structure and source-receiver distance.

Lemo and Chavez-Garcia (1994) have further tested the validity of Nakamura's

technique by examining two observations. According to them, if the Nakamura

technique iç valid, then we should observe the following:

i) The ellipticity computed at the surface (horizontal-to-vertical motion ratio)

should bear some resemblance to the one-dimensional transfer function

for vertical S-wave incidence.

ii) The ellipticity at the interface between the sediments and substratum

should be close to unity.

They examined data from two strong motion stations in Mexico City where

reliable geotechnical information is available. The results for the first test show

that the frequency of occurrence of the highest amplification peak of the 1 D

transfer function is in very good agreement with the ellipticity at surface, although

there was a significant difference in amplitude.

They tested second assurnption by cornparhg S-wave transfer function at

surface and the ellipticity for different modes of Rayleigh waves at the base of

stratigraphy. The sites chosen for this test had reliable information of P- and S-

wave velocities from boreholes. They observed ellipticity of near one at the

fundamental resonant frequency of the stratigraphy, which is in agreement with

the second assumption. However, for higher modes of Rayleigh waves, this

assumption does not hold.

Castro et al (1 997) test the following two hypotheses of Nakamura's Technique:

i) The vertical component of ground motion should not be significantly

amplif id.

ii) The spectral amplitude of the vertical and horizontal components at the

base of the sediments should be approximately equal.

They used a data set of accelerograms from 10 earthquakes with magnitude

between 4.7 and 6.6. Accelerograph stations located on different geologic

conditions in the region of Fruili, ltaly (including rock sites) recorded the ground

motions. Regression results indicate that low vertical amplification factors were

obtained for most of the stations (bath rock and soil). This implies that the vertical

component of S-wave arriva1 is approximately free of site amplification effects

(within a factor of 2). However, when the signal is contaminated by surface

waves, the variability in apparent vertical amplification effects increases.

Regarding the validity of the second assumption, the authors suggest that it still

needs further testing. Since the borehole method allows a direct determination of

the seismic response, the authon propose that data should be obtained from

well-instrumented boreholes, and used to test the validity of second assumption.

2.13 SUMMARY OF REVIEWED ARTICLES

I AUTHORS OF STUDY

1 Lermo & Chavez- Garcia. 1993

2 Lermo & Chavez- Garcia, 1994

3 Lachet & Bard,

FOCUS OF STUDY

To show that it is possible to estimate the empirical transfer function without a reference station

To review the applicability of micro- tremor measurements in evaluating site response of soft soils. To evaluate three techniques using micro tremor measurements

To investigate the characteristics of HN ratio and ils sensitivity to various parameters

Data set: consists of S-wave part of earthquake events. It has 6 earthquake events from 1985 - 1990 for Mexico city, 12 events in 1991 for Oaxaca, and 8 events from 1989 - 1990 for Acapulco. Results of study strongly suggest that site effects can be evaluated using spectral ratio from one station. The results hold good where amplification is caused by simple geology, There is a goad agreement between results from Nakamura's ratio and those obtained from standard spectral ratio technique

Data set is the same as used in the 1993 study of Lemo and Chavez- Garcia for the three cities of Mexico. Results show that micro tremor measurements allow for determination of the dominant period of amplification with good reliability in the range 0.3 to 5-hz, The three techniques compared were: direct computation of amplitude spectra, computation of spectral ratios relative to a f im soi1 reference station, computation of spectral ratios between horizontal component relative to vertical components of motion. Findings of study show that best results were obtained by the third (Nakamura's) technique, which afso provided a rough estimate of amplification.

Data set: consists of synthetic calcutations for 15 soit profiles, Resuits of the study indicate that for noise-simulated data, the position of lhe peak is independent of the source excitation function. Ratios for SV waves show several peaks whose position is independent of incidence angle. The peak position is influenced by the geological structure, Shape of HN ratio is controlled by the polarization curve of fundamental Rayleigh waves. The ratio is a reliable indication of the resonance lrequency of a horizontally layered structure. The amplitude of HN peak is sensitive to velocity contrast, Poisson's ratio, and source-receiver distance,

AUTHORS OF STUDY

4 Field and Jacob, 1995

5 Duval et al, 1995

6 Tevez-Costa et al, 1 996

7 Theodulidis et al, 1 996

To compare and test site response estimation techniques.

To check the stability of resutts obtained by HN ratio. To map the site effects by spatial interpolation of HN curves

To characterize the seisrnic behaviour of alluvium layers in the study area using micro tremor measurements.

To check the use of HN ratio technique as an indicator of site effects and to check the stability of the results

DATA SET AND FINDINGS OF THE STUDY

Data set: 1989 Loma Prieta earthquake aftershock data collected in Oakland, California, Results: The results for the non-reference site-response estimation techniques reveal frequency dependence of site response at sediment sites. (For bedrock sites, the response is flal and near unity.) The authors observe that revelation of frequency dependent character of site response by the non-reference site methods is prornising for site-specific hazard assessments in regions lacking adequate reference sites

Data set: consists of micro tremor recordings in Nice (France), Resuîtsr The study establishes the stability of HN method. The interpolation of HN curves is very close to the ewpected results, The frequency accuracy is rernarkable, For civil engineering purposes, maps of spectral site effects cari be obtained. By increasing the density of measurernents, the spatial definition can reach the precision of a building scale.

Data se!: is comprised of two sets of micro-tremor measurements in the town of Lisbon. Results: The study confirrns the fact that micro tremor recordings give reliable information about seismic behaviour of thin alluvium layers, HN ratio gives a good estimate of the resonant frequency for the surlace soft layers, The evaluated predominant frequencies correlated well with the depths of the alluviat deposits.

Data set: consists of 110, three-cornponent accelerograrns recorded at five different depths in Southern California, The magnitude range is 3.0SMLS4.6. Results of the study show that by computing the mean of the data set obtained at different depths, the results are quite stable. This is confirmed by a low standard deviation from the mean. There is a rernarkable difference in amplitude between the observed HN ratio and spectral ratio. This point needs further research, The focal mechanism radiation pattern does seriously affect the ratio amplitude. The influence of quality factor is negligibie on the shape and amplitude of the ratio.

AUTHORS OF STUDY

8 Bonilla et al, 1997

9 Castro et al, 1997

10 Bour et al, 1998

FOCUS OF STUDY

To find the variability of site effect estimation using S-wave, Coda, and HN methods.

To test the hypothesis involved in detemining the response of soils using HN spectral ratio technique.

To identify and map zones of homogeneous seisrnic response using Nakamura's technique,

DATA SET AND FINDINGS OF THE STUDY

Data set: consists of aftershocks of 1994 M 6.7 Northridge, California earthquake. A total of 38 aftershocks from M 3.0 to 5.1 wereused. Results: Findings regarding the comparison of HN ratio method and the direct spectral ratio rnethod suggest that HN ratio method extracts the same predominant peaks as the direct spectral ratio. However, the amplification levels from the two methods are different.

Data set: contains accelerograrns f rom 10 earthquakes with magnitudes between 4.7 and 6.6 for Fniili, Italy. Results: The study examined two assumptions of the HN method. (i) The vertical component of ground motion should be free of amplification, (ii) The spectral amplitudes of the vertical and horizontal components at the base should be the same. Test of the first assumption shows that low amplifications were obtained for the vertical component of S-wave arrival. However, when S-waves are contarninated by surface waves, the results are more uncertain, Conclusions coutd not be reached for second assumption as it needs further testing using borehole data

Data set: consists of 137 measurement points over a region of 60 km2 in Rhone Delta (South of France) during 1995 and 1996. Results: The study shows that HN ratio approach provides a simple means of determining the predominant frequency of a soi1 site. In comparison with a numerical modeling technique, the results obtained from the two methods are similar for formations tess than 10 m thick and the hamonics of fundamental resonance frequency are missing from the HN ratio spectral ratios, The findings also suggest that Nakamura's technique is a useful tool for establishing a seismic microzonation of the whole studied region, Also, the data obtained for the technique gives reliable information on the seisrnic behaviour of thin, gently dipping surficial layers.

CHAPTER 3

DATABASE AND PROCESSING

3.1 INTRODUCTiON

This chapter describes how the eaithquake database was compiled and

processed. The data set consists of time series of earthquakes of magnitude 4 to

6 from 1993 - 1996, plus events of M 2 2 from 1998 - 1999. The choice of data

set was based on data availability. The list of events for 1993 - 1996 was

prepared (in 1997) by downloading the event attributes from the lnternet site of

the Geological Survey of Canada (www.seismo.nrcan.gc.ca). From this list,

events from magnitude 4 - 6 were chosen according to certain criteria discussed

in the next sections, Tirne series data of these chosen events were obtained

from the Geological Survey of Canada (GSC) and converted to SAC (Seismic

Analysis Code, Lawrence Livennore National Laboratory) format using the

scripts provided by the GSC. These data were processed using the SAC

software package [www-ep.es.llnl.gov/tvp/sac~manual]. Two time windows of the

data were selected. One was the noise window, preceding the earthquake, and

the other was the signal window, containing the strong part of the S-wave

motion. The time series in these windows were Fourier transformed and

smoothed over log frequency increments of 0.1 units. The output files gave the

values of the Fourier velocity spectnim sampled at 0.1 log frequency units

(smoothed within the log frequency bins), covering the frequency range from 0.1

to 20-hz. The 1998 - 1999 data (magnitude 2 and over) were downloaded from

the GSC using the autodn (Automatic Data Request Manager) facility

[Hp.seismo.nrcan.gc.ca], Fourier transfomed, and tabulated in the same format.

The autodrm facility allows download of waveforms within a time period of about

two weeks following the event (thus these events were readily obtainable).

3.2 RECORDINO STATIONS

As the first step of data collection, the information was organized in the form of

two lists. One describes the recording stations and the other describes the

earthquake events that were analyzed. The list of recording stations was

obtained from the GSC [www.seismo.nrcan.gc.ca]. From this list, three-

component broadband recording stations were chosen, because they recorded

al1 the three components over a broad frequency range. Table 3.1 shows

selected stations. Tables 3.2 and 3.3 (next sections) show the analyzed events.

(Note: Location of events and stations are also shown on Fig. 5.1)

Table 3.1 List of recording stations.

Table 3. f continued.. . .

CNSN

CNSN CNSN

CNSN

1 CNSN YKWI [ 62.492 1 -1 14.742 1 0.2M) 1 YELLOWKNIFE. N.W.T 1 19940920 1 STS-IV ]

3.3 PROCESSING FOR EVENTS FROM 1993 - 1996

The events from 1993 - 1996 were obtained from the archives of the GSC.

These data were augmented by recent events that were downloaded from the

GSC using their autodrm facility (as described in the next section).

3.3.1 DATA SELECT ION

For the GSC earthquake catalogue of 1993 - 1996, events with the following

attributes were selected:

(i) Magnitude 2 4 (Based on catalogued magnitude value)

(ii) The event was recorded by at least three stations within the following

distance range:

<5OQ km for M 2 4

ELEV (KM)

0.363 0.419 0.015 0.675 0.005 0.400 0.550 0.01 5 0.243 0.518 0.281 1.400 1.292 0.205 0.180 0.200

NAME

CALEDONIA MTN., N.0 LAMALBAIE,QUE. MOULO BAY, N.W.T MORSBEY, 6.C SIDNEY, 6.C PEMBERTON MEADOW ,B.C

LONGI- TUDE

-64.806 -70.327 -1 19,360 -1 31.898 -123.451 -123.076 -1 19.617 -94.900 -79.142 -66.783 -95.875

-1 13.91 1 -1 34.881 -1 14.509 -1 14,605 -1 14.61 6

STA- TION

LMN LMQ MEC MOBC PGC PM6 PNT RES SADO SCH ULM WALA W HY YKW 1 YKW2 YKW3

INSTALL- ATION DATE 19930726 N.A 19920603 19960226 19931 105 19931 1 12

LATC TUDE

45.852 47.548 76.242 53.1 97 48.650 50.519 49.317 74.687 44.769 54.818 50.250 49.059 60.660 62.493 62.425 62.561

INSTRU- MENT TYPE CMG-3E STS-1 V CMG-3E CMG-3E CMG-3E CMG-3E CMG-JE

. CMG-3E CMG-3E _ CMG-3E CMG-3E CMG-3E CMG-3E STS-IV ,

STS-1 V STS-1 V

PENTICTON, B.C RESOLUTE, N.W.T SADOWA, ONT. SCHEFFERVtLLE. QUE. LAC DU BONNET, MAN. WATERTON LAKE, ALB. W HITEHORSE, M YELLOWKNIFE, N.W.T YELLOWKNIFE. N.W.T YELLOWKNIFE, N.W.T

19930203 19920603 19940720 19940327 19941207 i 9920603 19930827 19940920 1 9940920 19940920

4300 km for M 14.5

These constraints were established to ensure good signal strength. Under these

criteria the signal to noise ratio is generally very high (much greater than 2).

Using these constraints, the following events were chosen (Table 3.2)

Table 3.2: List of selected events from 1993 - 1996.

b

,NO- ; 1

DATE 19930129.0705001

LONGITUDE -128.546

LATITUDE - 49.309

MAGNITUDE 4.30

DEPTH (KM) 10.0

Table 3.2 continued.. . .

Note: Depths of O and 10 km are generally fixed, when the focal depth cannot be detemined by data.

3.3.2 DATA COLLECTION

The data were obtained from GSC, with the help of Bill Shannon. They are

stored at GSC in optical disks in two compressed data formats referred to as

SEED and CA formats. Each event was individually extracted from the optical

disks and copied in the workstation at GSC. It was later transferred by DAT

tapes to the Carleton University Seismology laboratory for further processing .

NO. 34 35 36 37 38 39 40 4 1 42

DATE 19960208.061 9003 1996031 0.21 12001 1996031 1.1 120001 19960314.1042014 1996031 6.2318001 1996031 8.0801 003 1 9960503.0404007 1996071 4.1 530001 1 9960721.2038006

DEPTH (KM) 0.0

10.0 0.0

18.0 10.0 38.4 4.1 0.0

MAGNITUDE 4.73 4.31 4.1 3

.. 4.36 4.40 4.9 1 5.50 4.00

LONGITUDE 1 LATITUDE ' -1 31.297 -1 30.436

_ -1 31 -61 7 -74.396

-1 30.331 -1 27.306 -1 21.876 -1 31 -262

5.00 1 0.0

63.353 50.573 63,449 45.925 50.471 49.689 47.760 63.325

- -1 37.577 64.371

3.3.3 DATA PROCESSING

The data were processed with the aim of obtaining the Fourier çpectra of the S-

wave and noise windows. The S-window contains the strongest part of the

shaking. The noise window is a pre-event sample. Windowing was done using

the SAC2000 software [www-ep.es.llnl.gov/tvp/sac-manual]. Therefore. the first

step was to convert the data to SAC format. Data from 1993 till about mid June

1995 were in SEED format. After that till the end of 1996, they were archived in

CA format. The scripts to do the format conversions were obtained from GSC.

These data conversion procedures are discussed in the following paragraphs:

SEED data were converted to SAC using the RDSEED utility program, which

extracts data for the specified start and end times of the event and the Julian day

of the event (since SAC only accepts Julian days).

Data after mid June 1995 were archived by the GSC in CA format. Conversion

from CA to SAC format was a two-step procedure; data were first converted from

CA format to SEED format, then from SEED to SAC.

Most of the steps of data conversion were iterative in nature. Therefore, several

macros (command files) were created within SAC to speed up the work. For

example, to extract the desired data window, two macros were created with the

names of NOISE and SIGNAL. These macros were used to select the noise and

signal windows, take their Fourier Transfomi, write the transfomed files in

alphanumeric format and then move them to their proper sub-directories.

Basically, the rnacro reads the time series files specified by the user. After that, it

shows the plots for al1 three components of the station. From these plots, I would

choose the star? and end times of the noise window. The ending time of this

window should be jus? before the arriva1 of the Primary wave. The window length

is about 30 - 40 seconds on average. (This length is later nomalized ta the

length of the signal window). The start and end tirnes will be approximately the

same for each component. These values are then used in the "cut" cornrnand of

the macro, to select the portion of the data between the two tirnes. Then the

selected time series is Fourier transformed by FFT and written in alphanumeric

format. The macro creates a directory called NOISE. It also gives a listing of al1

the created files and moves selected files to the NOISE directory.

The SIGNAL rnacro runs exactly the same way to facilitate the creation of the

SIGNAL directory. The idea is to create a wellsrganized directory structure of

signal and noise windows for al1 events.

3.3.4 THE OUTPUT

The alphanumeric Fourier transformed data were used to obtain summary files

of the signal and noise values. This was done using a simple FORTRAN

program provided by Atkinson (Carleton University), which smoothes the log

amplitudes over specified logarithmically-spaced frequency bins. This program

summarized the output of each seismogram in the form of records of two lines

each. The first line gives the event and component name, azimuth, distance and

start and stop tirnes of the window. The second line gives 24 values of smoothed

Fourier velocity spectrum, sampled in 0.1 log frequency units, beginning at log f

= -1 (i.e. frequency = 0.1 -hz to 20.0 -hz). The spectrum values are given in log

units. They were not corrected for instrument response, as it is the ratio of

horizontal to veitical components that is of interest. Division of H N autornatically

removes instrument response, as it is the same for both horizontal and vertical

components.

3.4 PROCESSINO FOR EVENTS FROM 1998 - 1999

The data from May 1998 to July 1999 were collected from the GSC using their

autodnn facility. This facility provides online access to data for events within the

last 15 days. (Note: The autodm capabilities are rapidly improving and will soon

provide data over a much longer period). The processing of these data was done

by Eleanor Sonley (Carleton student). These data had fewer constraints

regarding distance between the event and the recording stations. (Due to greater

ease of the data extraction process, we were less restrictive over selected

records.) For each record, the portion of the spectrum for which signal to noise

ratio was 2 or more was chosen. Events of M 1 2 were considered. From these

data, WV ratios were calculated using a FORTRAN program. A list of the recent

events is shown in Table 3.3.

Table 3.3: List of events from May 1998 to July 1099 L

MAGNITUDE No.

1 2 3 4 5 6 7 8 9

10 11

LATITUDE

45.1 8 62.01

. 57.83 48-71 82.92 81.13 58.31 58.22. 58.38 61 .16 58.31 51 -1 4 . 48.89 53.52 48.1 5

- DEPTH (KM)

OATE

98051 8.153920 980520,04381 4 980521 .O20529 980531,110225 980603.095940 980609.00341 3 980610.031016 98061 0.171950 98061 1.025556 980611.113720 980611.160015

23 24 25

LONGITUDE

-74.00 -1 24.10 -60.94

-1 28.65 -1 78.50

-89.63 - 1 33.54 -1 33.63 -1 33.49

-60.54 -1 33.54

--- -1 24.89 - -1 29.03

-1 17.57 -1 28.90

-79.90 -1 32.58

3.0 18.0s

1 2 13

16 17

980625.2251 54 980629.1 21 155 980702.003132

3.6 4.0 3.7 4.6

, 98061 1.1 85426 98061 2.202435

0 . 0 ~ 1 8 . 0 ~ ~ 0.1

18.Og

1 8 1 9 20 21 22

98061 4.084856 98061 4,180420

26 1 980702.052436

14 15

53.09. 53.1 4

1O.Og 18.09 33.49

49.99 59.42 48.83

27' 28 29

5.3 ' 3.0 3-1 3.2 3.5 3.0 2.5 4.2 2.8 2.7 2.6 2.9

98061 3.1 95023 98061 4.01 1240

98061 5.0851 02 98061 6.1 94955 98061 7.200654

,. 980625.021 551 980625.031751

0.Og 35.09 20.09 1O.Og

58.04 ~

. 71 -69 67.97 48.83

980702.083326 . 980702.132916

980707.23301 9

5 . 0 ~ 5.0g 5.0~1 5.0q

18,Og 5.09 5.09

10.0q 5.0q 1 .Og

18.0% 20.09

10.0~ 18.0~ 0.19 1.8q

10.0~1 10.09 10.Og. 18.0q 10.0~ 5.0g

1 0 . 0 ~ 0.0g

20.09

1 30.24 -73.98

-1 25.60

59.68 1 -75.94 61.47 f -78.89. 45.95 1 -74.90 52.77 1 -34.67

4.5 3.1 2-7

-1 36.79 -1 35.32 -1 43.81 -1 29.56

30 31 32 33 34

3.6 .~

3.1 2.8 5.1

1 4.4 52.73

2.6 3.0 3 . 1 3.2

.. 43.65 -73.74

-1 30.33 -66.1 4

-1 29.1 4

0.Og 18.0q 1 8 . 0 ~ ~ 18.0Q 18.09, .. -35.73

4-1 2.5 3.7 3.1 4.3

35 36 37 38 39 40 41 42

980709.01 1 71 6 1 60.67 980709.01 521 3 1 44.80-. 98071 0.030500 f 50.55 98071 3,000000

, 980714.010535 , 49.36-.

48.73 98071 4.01 4949 98071 4.04401 7 98071 4.1 50501 98071 5.00301 6 98071 5,070804 98071 6.1 34653 980720.122700 980721.004804.

48.77 -129.01 1 3.7 50.57 72-78 47.52 47.02 50.03 62.26 54.99

-1 30.43 1 2.5 -74.04 1 3.3

-1 29.20 [ 3.5 -66.61 1 4.0

-1 30.23 f 2.6 -58.00 1 2.8

-1 34.00 1 2.7

I

Table 3.3 continued.. . .

OEPTH (KM) 18.0g 18.09 18.0g, 18.0g 5.09 10.0~ 10.0~ 10.09, 35.0g 20.09 10.09 1 O.Og 10.0~ 18.09 1 .OQ 18.0~~ O .OQ 18.0g 18.0~~~ 10.0~ 10.04 3.5 0.0~ lO.Og,

LONGITUDE

-76.1 5 -7 1.22 -74.69,

-1 18.88

LATITUDE

46.35 46.1 7 46.1 9 76.03 62.49 51.34 72.32 51.34 71.85 52.1 3 49.00 48.88 48.88 49 .O5 60.00 61.80 51,71 51.81 60.08 50.94 49.01 53.93 50.37 50.36

No.

49 50 51 52 53 54 55 56 57 58 59 60 61 62

, 63 64

, 65 66 67 68 69 70 71 72

MAGNITUDE

2.7 4.4 2.5 3.4

DATE

980730,022259 980730.085722 980730.1 02931 980730. t 13826 980730.1 6531 9 980731 .O74028 980731.074042 980731.081 801 980803.072520 980806.024300 980806.180519 980806.t 81 11 8 980806.181723 980808.082310 980811.192824 980812.061029 980813,113832 98081 3.1 13833 98081 4.1 851 35 980816.1 31205 980816.131942 980818.080754 98081 9.043905 9808 1 9,050456

43.87 57.76 50.9 1 49.1 4 50.91 50.69- 50.74 50.73 60.84

73 74 75 76 77

, 78 791

-75.76 -1 36.61 -1 30.66 - 127.77 -1 30.65 -1 30 $54 -1 30.56 -1 30.58

1 -1 40.34

980024.1 92733 980827.025435 980830.1 13333 980901.091 942 980901 .1 20203 980901.145200 980901.161803

-1 25.09 1 3.2 -1 30.78 1 4.0 -74.70 1 3.8

-1 30.80 -1 33.30 -1 31 -64 -1 29.1 1 -1 29.22.

3.1 3.9 - 6.0 -

4.0 . 3.0

3.1 3.6 4.6 2.9

82 83 84 85

, 86 87 88 89

, 90, 91

, 92 93 94 95 96

3.6 3.9 4.4 3.1 4.1 ,

18.0~ 5.09, 10.09 10.0C1 10.0~ 10.0~ 10.0~ 10.09 5.0g

980905.051905 980906.075002 980906.1 51 601 980907.1 44004 980908.191305 980909.144804 96091 0.232926 98091 1.083206 980911.21361 1 98091 2.081654 980913.005513 98091 3.032843 98091 3.062334 980913.170412 98091 4.0221 47

801 980901.181249 81

44.20 1 -68.71

-1 29.35 -68.33

,. -1 40.00 -65.99

-1 16.05 -1 15.75 -73.60

- 1 30.79 -1 28,14 -1 31 -78 -1 30.35 -1 30.24

2.5 3.5 3.1 3.2 4.0 4.6 2.8 2.6 2.6 2.6 2.6 3.2 2.7 3.7 3.3

980901 -235602

60.16' 60.1 8 59.55 40.07 4.16 50.96 50.04 51 .O4 56.55 58.85 58.29 46.86 56.33 59.01

4.5 2.9 3.2 0.3. 3.6 3.8 3.2 3.1 2.6 3.4 4.3 2.5

18.0q 18.0g 18.0q 0.09 18.0~ 20.09 10.09

. 10.09 10.0~ 10.0~ 5.0g

. 0.0% 18.0g 10.0~ 10.0g

-73.38 -73.38

-1 36.24 -52.53

-1 33.94 -1 30.33 -1 30.64 -1 30.52 -1 34.42 -1 36.78 -1 36.85 -76.95

-1 36.1 1 -1 35.74

Table 3.3 continued.. . . OEPTH (KM) 10.0g 18.09 10.Og

. 18.09 10.0s 10.09 10.Ogj 0.04 10.0g. 10.0g 10.0~. 18.Og 5.09 18.09, 18.0~ 1O.Og 10.0~~ 10.0&

1 15 980930.1 62627 4.4 18.09

No.

97 98 99 100 101 , 102 1 03 1 04 105 1 06 1 07 108 1 09 t 10 1 1 1 1 12 1 13 1 1 4

LATITUDE

60.95 45.48 59.1 2 49.06 49.96 49.95

,. 49.90 62.45 50.93 49.89 48.90 46.50 41 -57 46.47 45.88 50.02 48.90 51 .1 O

DATE

98091 5.1 90654 98091 6.07491 5 98091 7.203200 98091 8.21 3005 98091 9.1 42528 980920.084924 900920.122400 980921,1321 O0 980921.213122 980924.000053 980924.1 20642 980924.181 559 980925.1 95255. 980927.081 802 980929.01 0341 980929.074252 980930.111522 980930.133446

LONGITUDE

-1 38.54 -67.27

-1 35.1 9 -67.59

-1 30.25 -1 30.25 -1 30.28 -1 25.05. -1 30.60 -1 30.26 -1 28.1 4 -76.31 -80.35 -76.21 -75.35

-1 30.09 -1 29.1 3 -1 30.75

MAGNITUDE

3.0 2.5 2.8 3.6 4 .7 2.8 2.9 3.0 2.8 3.0 2.8 2.8 5.4 2.7 2.8 3.1 3.7 2.7-,

L

Table 3.3 continued ....

DEPTH (KM)

9.8, 5.09

18.0% 5.09 0.09, 5,Og

1 18.0g

MAGNITUDE

2.6 2.9 4.1 3.3 2.6 3.3 2.5

152 153 154 155 156 157 158 159 160 161 162 163 1 64 165 166 167 168 169 170 171 172 173 174 175

, 1 7 6 1 T7 1 78

, 179 1 80 181

, 182 1 83 184 185 186 187 188 189 190 1 91 1 92

No. L

145 146 147 148 149 150

DATE

981 021.074451 981 022.205422 981 022.094335 981 022.175218 981023.153350 981023.220113

LATITUDE

47.56 58.29 49.34 58.1 9 56.34 58.24

151

LONGITUDE

-70.28 -1 33.56 -66.88

-1 33.59 -1 17.02 -1 33.56

981024.171010 981 027.235653 981 027.182335

48.64 58 .58 58.26,

-1 29-22; -1 37.64 -1 33.61

-73.82

981027.194300 981029.121853 981 031.183044 981031.192444 981031.182521 981 102,043905 981105.013317 981106.150123 981 107.205124 98 1 1 07.205340 981 108.21 2208 981 108.041540 981 109.203452 981109.193217 981 110.01 3246 981 1 11 .21 4541 981111.115942.

981023.070223 45.71 2.5[ 2.6 3.2

10.09 5.0g 5.0g

58.22 60.1 3 60.21 60.1 2 60.1 5 65.81 49.06 62.25

5.Og 10.Og 1O.Oq 10.Oq

1 0.09

3.4 3.1 4.4 4.0 4.3 3.2 2.5 2.8

-1 33.56~. -141.14 -1 40.96 -1 41 .O1 -1 41 .O1 -90.53 -67.89

-1 42.92

5.0g 0 . 0 ~ 5.0g

10.0g 5.0%

18.Og 18.0q 0 . 0 ~

981 1 12.0341 30 981 1 12.063823 981 11 7.1 52643 981117.174606 981119.084315

t O.Og 10.0~ 18.09

. 10.0~ 0.0% 5.0s 5.0g

10.0s 10.0~

50.52 50.57 60.81 48.13 59.52 59.40 59.42 57.29 48.49

-1 29.65 -1 19.29 -1 30.1 8 -131 -28 -1 25.38

61 36 48.15

,. 50.43 51 $21 62.62

2.6 2.8 2.8 2.5 3.1

981 120.031525 981 121 .O32833 981 123.070916 98 1 123.082549 981 123.123620 981 124.184207

-1 37.50 -70.39 -90.84 -91.95 -90.22

-1 30.29 -1 40.57 -1 30.34 -82.63

-1 30.40 - 1 30.33 -43.93

. -1 19.30 -1 36.58 -1 39.1 1 -1 39.1 5 -1 36.74 -1 03.99

70.60 74.44 79.94 79.97 79.83 51 .O1

3.0 2.5 4.5 2.6 3.2 4.0 4.3 2.5 3.5

3.9 3.1

981 126.1 4223 1

981 124.21 5527 981 124.1 35047 981 125-025507

35.0q 18,Og

,. 2.7 2.5 4-1 2.6 3.1 2.6 3-1

64.1 8 . 50.47

41.10 10.09 18.09 18.09 18.0~ 5.0g 10.0

t8-Oa

60.85

3.6 ' 3.1 3.2 2.5 2.8 33 3.2

-1 38.01

18.0~ 18.0~ 18.09 10.09 5.09

10.09 5 . 0 ~

-77.00 -59.04 -74.29

-1 36.71 -1 31 -79 -59-42

981128.163851m 981 128.221 125 981 201.050220~ 981203.041248 981 205.01 5450 981 206.021 255

45.78 61 -04 46.59 58.69 53.94 60-41

Table 3.3 confinued.. ..

LONGITUDE

-79.83 -1 38.22 -1 27. t 8 -1 36.45

LATITUDE

52.68 63.94 61.68 59.22

No. 1

193 194 195 196

DATE

981 207.1 33708 981 209.02401 8 981210.132632 981210.071512

197 981 21 1.203307 51.83 -1 31.40 198 981211.211131

MAGNITUDE

3.3 2.5 2.9 4.0

J

OEPTH (KM)

18 .0~ 0.0g

10.0~1 10 .0~

199 981 21 2.234601 60.90 200 981 21 3.1 40808. 58.52

-1 38.06 -1 42.25 -1 27.95 -1 31.56 1 35.04

-1 37.67 -1 24.09 -1 41.86 -1 34.66 -91 .O4

-1 15.24 -77.91 -70.29

201 202 203 204 205 206 207 208 209 210 211

2.6 3.6 2.6 7

4.5 2.5 3.1 2.7 2.7 4.4 4.6 3.6 4.2

212 21 3 214.. 215 21 6 217 218 21 9 220 221 222 223 224 225

981 214.133845 981 21 5.041 708 981 216.055403 981217.130337 981218.174141 98121 8.002257 981 21 8.093323 981 222.1 70435 981 222.01 1 747 981225.133026 981227.215159

0 . 0 ~ 10.0g 10.0a 5 . 0 ~

1 0 . 0 ~ 0.0g 5.Og

10.0~1 0.0%

18.0g 10 .0~ 18.0% 18.0%

3.0 5.3,

48.84 63.401

55.28 60.20 62.07 62.40 55.28 79.93 48.00 43.83 74.30

5 . 0 ~ 18.09

981229.231 504 9901 01.092810 990101,110103 990104.224117 9901 06.22031 3 9901 10.105216 990110.152044 9901 14.1 04736 9901 16.203059 9901 16.161234 9901 17.044904-. 9901 18.073529 9901 1 9.1 5091 7

1 9901 19.062320 226 1 9901 21.235055 227 1 9901 21.053824

, 228 1 9901 22.042725

47.03 79.86 48.48 59.09 77.43 42.87 42.86 72.96 64.65 61.98 59.94

.. 77.47 66.25 45.44

3.4 4.2 3.1 3.1 3.0 3.2 3.5 3.6 3.2 2.6 2.6 3.0. 3.0 2.8 3.5 2.5 3.4 2.6 2.6 2.7 3.3 2.9 2.5 2.6 2.7 2.51

-66.55 -1 10.24 -1 28.75 -1 36.50 -1 04.86 -71 .O0 -70.96

-1 13-62 -1 34.73 -1 33.57 -1 37.41 -1 05.04 -1 35.22 -74.53

49.24 59.47

10.Og 10.09 18.0g 2.09 2.0%

18.0g 0 . 0 ~ 0 . 0 ~ 0 . 0 ~

la.oa 10,Og 18.0g,

3.9 10.0q 18.09 5.0%

10,Og 10.09

3.0, 5.Og 0 . 0 ~

t8.Oci 5 . 0 ~ 5.09,

1 0 . 0 ~ 75-09

-1 23.63 -1 38.93

3-4 1 18-0a

1 49.1 3 1 -67.09 229 1 9901 23.202500' 60.49

49.89 49.81 48.85 42.79 59.98 45.92 42.31 42.33 60.1 2 48.26 49-26

230 231 232 233 234 235 236 237 238 239 240

-139.51 -1 30.21 -1 30.20 -1 23.43

-77.82 -1 37.43 -74.85 -82.31 -82.30

-1 41.1 1 -1 18.68 -80-94

9901 24.1 22007 990124.121541 9901 25.092757 9901 25.201 228 9901 25.060855 9901 26.081 428 9901 27.01 571 9 9901 27.01 3807. 9901 29.061 033 990131.110557 990201.222205

Table 3.3 continued.. ..

1 No. 1 DATE 1 LATiTUDE 1 LONGITUDE 1 MAGNITUDE 1 DEPTH 1 241 2 4 2 243 244 245 246 247

990203.231 659 990203.224832 990204.21 3620 990206.221 127 990207.1 30754 990207.095658 990207.004009

5.09 18.Og 18.Og 10.Og 10.Og 10.0g 0.0%

10.09

248 249 250 251 252 253 254 255

1 2.5 2 .5 2.7 2.7 2.5 2.5

60.1 1 49.74 49.81

256 257 258 259

(KM) 0.Og

18 .0~ 10.0g 10.09 1 0 . 0 ~ 10.0g

50.171 -1 29.62 1 3.1

.- -140.23 -66.98

, -1 30.21

99021 1.1 4491 2 1 51.1 5 10.0g

990214.133414 99021 5.1 60428 99021 6.210223

-1 25.83 1 2.7

50.56 1 -1 30.35

65.29 44.46 58.45

-88.1 8 1 -56.22

- 1 42-78. -1 44.26 -1 30.38 - 136.31 - 1 1 3.32

990221 .O33323 990221 -1 7341 1 990221.21 171 8 990223.1 1 1233

59.22 48.97

3.0 3.6 4.2 3.2 2.9 3.8 2.5_

-1 40.99 44.44

-1 06.60 -65.99

60.26 70.92 76.70 47.61

-1 38.49 - -129.87

-1 38.81 -1 9.54 -70.67

-1 30 ,26 -69.67

-1 24.38 -1 39.49

65.00 77.87 48.02 50.23 44.62 47.92 64.82

99021 7.075826' 99021 9.1 70220 990220,201638 990220.075942

2601 990223.151239

65.40 50.56 57.19 48.26

3.2 [ 10.09

261 , 262

263 , 264 , 265

266

4.1 3.7 2.7 2.6 3,8 2.7, 3.0 3.8 2.5

990223.1 80409 990223.01 1036 990225.204209 990226.033844 990228.141 026, 990301 ,SI 1925

267 268 ' 269. 270

1 8 . 0 ~ 18.09 5.09 0.0q

1 8 . 0 ~ 1 8 . 0 ~ 1 0 . 0 ~ 18.09 0 . 0 ~

2.6 [ 10.0& 2.51 5.09

990302.050609 1 50.55 1 -1 30.20 4.0 3.2 2.8 3.2 3.8 2.8 3.0 2.8 2.6 2.6 5.1 3.4 3.5 2.5 2.5 2.9 2.6 3.4

990302.071 1 1 O 990303.1 52631 990306.014541

18.09 18.09 0.0~1

10.0~1 9.6

18.0g 10.0q 18.09 18-09 18.0g, 18.Og 0.09 0 . 0 ~

18.0g 18,Oq 10.0~ 10 .0~ 0.0q

l 271 , 272 , 273 l 274 , 275

276 277 278 279 280

, 281

49.62 66.72 45.96

286 , 287

288

76.54 . - 67.69

64.86 49.03 53.39 46.04 44.77. 45.89 49.61 49.62 49.61 65.42 62.34 49.62

18.0q

990306.103340 990307.034215 990308.1 13804 990309.120704 99031 5.1 43235 990316.17331 1 99031 6.1 5041 5 99031 6.1 25048 99031 7.1 75059 99031 7.052700 990317.085537

-66.38 .. 990322-06031 1 990323.015334 990325.1 40608

-91.62 -93.52

-1 34.09 -1 28.73 -1 31 -47 -74.99 -73.83 -74.38 -66.31 -66.34 -66.32

-1 34.24 -124.16,. -66.32

2.5

-66.29 -1 30.31 -1 29.20

. -1 40.88

282 283 284

-1 35.51 -74.86

3.71 20.09 3-01 18-OQ

99031 7.1 42655 1 49.61 99031 8.060003 99031 9.130127

285 [ 990321.223054

50.57 47.40 61.60

Table 3.3 continued.. . .

DEPTH (KM)

18.0% 18.09 1O.Oq 0.Og 0.0g

10.09 10.0~~ 0 . 0 ~ 45.0 0.Og

h

No. I

289 290 291 292 293 294

LONGITUDE

-66.39 -72.94

-1 37.45 -1 38.87 -1 37.33 -1 29.82 -1 38.67 -1 37.27 -1 23.26 -1 37.42

299 300 301 302

3.11 18.0q

MAGNITUDE

2.7 3.3 3.0 2.7 4.0 2.5 2.8 2.7 3.3 2.8

DATE

990330.155136 990330.133014 990401 .O51 139 990401 .O1 3523 990402.063959 990402,005705

990403.21 5007 990406.180632 99041 0.09571 3 99041 1 .O00537

3.6 ,. 3.5

2.7 3.1 3.2 2.5 2.5 3.4 2.8 2.8 2.5

,. 3.3

72.88 1 -90.95

LATITUDE

49.63 59.81 59.69. 57.97 59.1 7 50.87

303 304

, 305 306 307 308 309 31 O 31 1 31 2

18.0g 18.0~ 30.2~ 18.0$ 18.0~

9.2 18-09 1O.Og 10.09 10.09 1O.Og 0.09

62.32 56.82 48.21.

t 0 . 0 ~ 0.Og 0.0g 0.0g

10.09 10.09 0.09

10.09 l8.0g 18,Oq 18.0g 18,Oq 18.0~ 5 . 0 ~ 0.0~ 0.0g

59.63 59.1 9 48.36 58.76

295 f 990402.134051

-71.1 6 -51.55

-1 22.86

31 6 31 7 318 31 9

, 320

296 297 298

2.7 3.3 2.5

1 2.9 58.1 0 62.02 6 t .59 58.03 60.24

990429.190430 990430.080256 990501.012131 990503.160848 990504.050304

990402.072549 990403.1 72922 990403.094458

-64.26 -66.82 -70.47 -92.72

-1 28.98 -1 30.38 -1 19.32, -1 30.30 -1 37.54 -1 41 .O4

99041 4.002833 9904 t 4.1 64635 990418.202100 990422.235641 990422.005641 990422.055538 990422.095324 990422.073016 990424.070907

5.0g 18.09

1 .O 5.0g

-65.99

67.49 68.1 8 47.44 72.39 48.70 50.52 52.32 50.53 60.1 7

31 3 1 990428,005347

321 322 323

, 324 325 326 327 328 329. 330

-1 24.37 - t 39.33 -66.60 -66.08 -76.37

-1 43.20 -1 24.07 -1 40.94 -1 39.00

. -1 40.92

47.94 60.04 47.00 60.90 47.1 1

332 , 333

334 335 336

62.58

3.3 3.5 3.8 2.9 2.7

-1 35.72 -1 25.1 7 -1 29.42 -64.47

-1 07.04 -1 06.99 -79.07 -71.98

-1 40.63 -1 28.65 -1 29.99

990521 -1 10051 990524.052235 990525.162808 990526.1 151 30 990530.093042

990425.0921 33

2.8 3.0 2.9 2.7 3.3 3.0 3.0 3.1 3.2 3.2 3.1

, 990504.1 74058 1 61.94

2.5 1 27.69 4.4 0 .0~

60.12

31 4 1 990429.21 0945

990505.1 7471 4 990506,181814 990512.082739 990512.050715 99051 2.1 60329 99051 5.0321 34 99051 6.050427 99051 8.204629 99051 8.06361 2

2.7 2.5 2.9

48.1 9 60.26 3 1 5'

64.95 49.51 63.33 76.69 76.60 46.98 62.1 4 59.95 63.87 69.74 331

5.0g 18.0g 18-09

-1 21 3 3 -1 41.57 990429.0441 07

990518.174009

Note: A 'g' beside the depth indicates it was fixed by the analyst.

Table 3.3 continued.. . .

DEPTH (KM)

18 .0~~ 0 . 0 ~ 0 . 0 ~ 0.0g

15.0~~ 11.2~1 18,Oq 18.0g 10 .0~ 0.0

,

18.0% 10.09

No. 1

337 338 339 340 341 342 343 344. 345 346

LATITUDE DATE

990530.1 43359 990601.1 75910 990601 .152237 990603.0321 39 990607.065218

. 990609.01 3501 99061 2.071 303 99061 8.231 908

.. 99061 9.092943 990620.1 95503

349 350 351

3.4 3.1

LONGITUDE

347 , 348

3.21 18.0g

MAGNITUDE

990620.2159441 73.91 -72.92 990621.072607 47.42 -1 28.94 990621.081 348 990623.200646 990624.1 13621

2.5' 2.5 4.6 3.2

2.6 2.6 3-4 3.1 2.9.. 2.8 3.4 3.5 3.7.- 3.2

46.55 1 -78.39

18.0g 5.0%

t O.Og , 18.0~1

, 354 355 356 357

, 358

59.43 58.1 8 64.59 63.81 47.70 69-94 46.47 47.72 52.60

72.91 50.12 62.1 3

990702.1 14529 990703.014354 990705.033458 990707.063728 990708.202353

352 353

-1 38.76 -1 38.38 -1 31 .O8 -1 31.37 -69.89 -85.34

,. -75.1 1 -1 28.95 -1 32.1 4

-74.54 . -71.22

-1 40.45 48.83 73.86

10 .0~~ O.Om 10.09 18.0g 0.0g

1O.Oq _ 0 . 0 ~

0.0%

359 1 990709.063329 360 1 99071 0.075149 361 1 990710.1 54025

990620.1 021 18 990701.1 12909

49.23 47.1 0 49.43 49.63 58.56 49.20

-1 29.29 -94.79

10.09 18.0~1

2.8 2.9

-1 29.43 1 5.7 -1 23.50 1 5.5 -1 29.41 1 3.5 -66.41 2.7

-1 37.31 -1 29.38

-1 29.30 -75.39

, 362 363

2.6 2.7 3.5 3.1

64.22 - 67.00--

99071 0.230523 1 49.4 1 99071 4.11 1 147 1 46.59

-1 40.66 -136.1 9

CHAPTER 4

HN RATIO RESULTS

4.1 IN1 RODUCTlON

The results obtained from the processed data are presented in this chapter. In

the first few sections of the chapter, the procedure for calculating the H N ratios

is discussed. Data from 1993 - 1996 were mainly manipulated in spreadsheet

software. Data from 1998 - 1999 were processed using FORTRAN programs

written for this purpose. Once these H N ratio values were obtained, some basic

statistics were calculated. These included average HN, standard deviation, and

the 90% confidence interval on the mean. These are shown graphically for each

station in the last section of the chapter.

4.2 HN RATIO CALCULATION

For the 1993 - 1996 data, there were two files for each event; one giving the

signal spectturn and one giving the noise spectrum. These were used to

calculate signal to noise ratio. Signal spectra for which the SIN ratio was greater

than 2 over the frequency band of interest were used in the results. For 1998 - 1999 data, the events were also processed to obtain the values of signal spectra

at frequencies for which signaihoise ratio was greater than 2. Then from these

data, the HN ratios were calculated. A detailed description of how the ratios

were calculated for the 1993 - 1996 data and for the 1998 - 1999 data follows:

4.2.1 RATIO CALCULATION FOR 1993 - 1996 DATA

For the 1993 - 1996 data, the output of the data processing was two files

providing the noise and signal spectra for each station for each event. The H N

ratios are calculated for the frequencies with signawnoise ratio greater than 2. To

find the signawnoise ratio, the noise spectrum was normalized to the same

window length as the signal window. This was done by squaring the noise

spectral amplitudes (to ensure energy conservation at each frequency), and then

multiplying by the ratio of length of the signal window to the length of the noise

window. The final normalized noise spectrum was obtained by taking the square

root. This procedure was perfomed in a spreadsheet program. (Due to the bulk

of the data, several template files were created with embedded links. The files

for each station of each event were created by changing the source of the links

in the ternplate file and re-saving the file with the associated naming convention).

The second set of template files was used to calculate the H N ratios using the

output of the above step. These too were modified in the same way and the H N

ratio files were saved according to the chosen naming convention. At this point of

processing, the minimum S/N ratio criterion was not applied. Rather, the values

of this ratio were also incorporated in the H N ratio files, and this information was

later checked in a FORTRAN program.

The noise and signal files were used in the spreadsheet program EXCEL to

calculate the normalized noise spectnirn. These files were used jointly ta

calculate the nomialized noise spectrum and the signal to noise ratio. The H N

ratio was then calculated in EXCEL (by creating template files; the links in these

files were connected to the output files created in the previous step). Since the

values of the signal were in log units, we took the difference between the

horizontal and the vertical components to obtain the log of the HN ratio. We

used the resulting value only if the SIN ratio was greater than 2. An example

template is provided in table 4.1.

Table 4.1 Calculation of HN Ratio.

Using the template of table 4.1, H N ratios were calculated for al1 of the data and

stored in different files.

4.2.2 RATIO CALCULATION FOR 1998-1 999 DATA

The data from 1998-1999 were manipulated through several FORTRAN

programs. The Fourier spectra were summarized using the program "stonbat.fof

by Atkinson, Carleton University. This produced the output spectral values in log

units, with signaVnoise ratio > 2, for 24 frequency bins (log f = -1. -0.9. -0.8. . . . . 1.3). Once these were obtained for al1 the data, the values were input to a

second program to calculate the WV ratios. The data were saved in different files

for different months. These files were later combined to one file for further

calculations of mean, standard deviation and 90% confidence interval of the data

for different stations.

4.3 CALCULATION OF MEAN HN

The final output to be obtained from the data is the rnean. standard deviation,

and 90% confidence interval of the mean for al1 of the stations. Since the data

were in two blocks, one from 1993-1 996 and the other from 1998 - 1999, they

had to be combined so that the results could be obtained for the whole data set.

Four FORTRAN programs accomplished these tasks. In the fint program. the

data from 1993 - 1996 relating to a particular station (e.g WALA) were selected.

In the second step, data from 1998 - 1999 for that station (WALA) were read

and merged with the 1993 - 1996 data to f o n a combined data set. In the third

step, the means for the combined data sets were calculated. In the fourth step,

the final statistics, like mean HN, including its standard deviation, and the 90%

confidence interval about the mean were calculated.

4.4 HN RESULTS

Mean H N ratios are plotted for each station in figures 4.1 - 4.3. On the same

graph, the standard deviation of obseivations, and the 90% confidence limits

about the mean are also shown. These values are tabulated in the appendix.

Figure 4.1 : Mean HN ratios, Standard Deviation, 90% confidence Interval for Eastern Stations

MEAN LOG HN FOR FR6

0.1 1 10 1 O0 Freq. (hz)

1

i - mean log HN + +,- st.dev 1

i - +,- 90% con. int

MEAN LOG HN FOR GAC

0.1 1 IO 1 O0 Freq. (hz)

/ - mean log W - +,- st.dev / - +,- 90% con. int

, l

MEAN LOG HN FOR SAD0

1 10 f req. (hz)

1 I i - +,- 90% con. int l I

MEAN LOG HN FOR DRLN

0.1 1 10 100 Freq. (hz)

-

MEAN LOG HN FOR SCH

-0.6 t -0.8 A

* -1 :

o. 1 1 10 100 Freq. (hz)

- mean log HN - . +.- st.dev - +,- 90% con. int

MEAN LOG HN FOR LMQ

O. 1 1 10 1 O0 Freq. (hz)

1 - mean log HN +,- st-dev j - +,- 90% con. int

MEAN LOG WV FOR LMN

0.1 1 10 100 j Freq. (hz)

i 1 ! - mean log HN - . +,- st.dev 1 i

î - +,- 90% con. int

MEAN LOG HN FOR A l 1

I '- mean log HN - - +,- st.dev - +,- 90% con. int

0.1 1 10 1 00 Freq. (hz)

MEAN LOG HN FOR A1 6

O. t 1 10 100 Freq. (hz)

j- mean log HN - - +,- st.dev - +,- 90% con. int

MEAN LOG HN FOR A54 1 - . ,il

0.8 :, i

0.1 1 10 100 Freq. (hz)

-- - /- mean log HN +.- st-dev i - +,- 90% con. int

MEAN LOG HN FOR A21

0.1 1 10 100 Freq. (hz)

t I- mean log HN - - +,- st.dev - +,- 90% con. int

MEAN LOG HN FOR A61

0-1 1 10 1 O0 Freq. (hz)

1 - +,- 90% con. int '.

MEAN LOG HN FOR A64 1 1 1

1

1 . . - .

0.1 t 10 t O0 Freq. (hz)

/- mean log HN . - +,- st.dev 1

i - +,- 90% con. int

Figure 4.2: Mean H N Ratios, Standard Deviation, 90% Confidence intervat for MidoCanada

MEAN LOG H N FOR WALA

0.1 1 1 O 100 Freq. (hz)

- mean log HN - - +,- st-dev - +,- 90% con. int

MEAN LOG H N FOR YKWl

-0.6 1 -0.8 1

-1 : . -7-

0.1 t 10 100 Freq. (hz)

I 1- mean log HN +,- st-dev 1 - +,- 90% con. int I

MEAN LOG HN FOR YKW2

0.1 1 10 100 1 Freq. (hz)

MEAN LOG HN FOR YKW3

r- mean log HN - - +,- st.dev

0.1 1 10 100 ,

Freq. (hz)

I 1 - +,- 90% con. int

-mean log HN - +,- st.dev i - +,- 90% con. int

1

!

MEAN LOG HN FOR YKW4

0.1 1 10 100 1 Freq. (hz) I

I I - mean log HN - - +,- st.dev

i - +,- 90% con. int

MEAN LOG HN FOR €DM

0.1 1 10 100 Freq. (hz)

r I 1 - mean log HN +,- st-de" 1 ' I , - +,- 90% con. int 1 !

MEAN LOG HN FOR ULM

0.1 1 10 1 O0 Freq. (hz)

) - mean log HN . +,- st.dev j - +,- 90% con. int

Figure 4.3: Mean HN Ratios, Standard Deviation, 90% Confidence Interval for SW-Canada

0.1 1 10 100 '

Freq. (hz)

MEAN LOG HN FOR PNT 1 r 1

: - mean log HN + - +,- st.dev I

- +,- 90% con. int

O .8

MEAN LOG HN FOR PMB 1

I

0.1 1 IO 1 O0 Freq. (hz)

0.6 I

- mean log HN - +,- st.dev - +,- 90% con. int

MEAN LOG HN FOR PGC

0.1 1 10 1 O0 Freq. (hz)

1- mean log HN - . +,- st.dev l

i - +,- 90% con. int

MEAN LOG HN FOR BBB

0.1 1 10 1 O0 Freq. (hz)

r - mean log HN +,- st.dev - +,- 90% con. int

Figure 4.4: Mean HN Ratios, Standard Deviation, 90% Confidence Interval for NW-Canada

MEAN LOG HN FOR DLBC

0.1 1 10 1 O0 Freq. (hr)

1 - mean log HN - - +,- st.dev 1 - +,- 90% con. int

MEAN LOG HN FOR WHY

-0.8 -1 i l . -

0.1 1 10 100 Freq. (hz)

-mean log HN - +.- stdev / - +,- 90% con. int l

MEAN LOG HN FOR MOBC

0.1 1 10 1 O0 Freq. (hz)

- mean log WV +,- stdev - +,- 90% con. int

l

MEAN LOG HN FOR MBC t

1 I

t i

0.1 1 10 Freq. (hz)

l

1 I- mean log HN +,- st.dev 1 1 1 - +,- 90% con. int

-

MEAN LOG HN FOR INK ! !

o. 1 1 1 O 1 O0 Freq. (hz)

i- mean log HN - +,- st.dev i I - +,- 90% con. int

MEAN LOG HN FOR DAWY

0.1 1 10 100 . Freq. (hz) 1

r

i - mean log HN +,- st.dev

1 - +,- 90% con. int

MEAN LOG HN FOR RES

0.1 1 10 1 O0 Freq. (hz)

- mean log HN - - +,- st.dev I - +,- 90% con. int

Chapter 5

CORRELATION OF HN RATIOS WlTH GEOLOGY

5.1 INTRODUCTION

This chapter discusses possible correlation of the HN results obtained in this

study with general geological conditions. The geology is discussed on two

scales: (i) regional scale geological units, and (ii) local surficial materials. These

sections are presented in the fom of tables and rnaps. The maps for surficial

materials were produced by modifying the digital release of 'Surficial Materials of

Canada: Map 1880 A' (Dr. R.J. Fulton, 1995) in a GIS software package (Arcview

3.0). The HN results of this study are then compared with reference to the

general geology and are presented in tables 5.3 - 5.8.

5.2 GENERAL GEOLOGY

5.2.1 MAIN GEOLOGICAL REGIONS

Canada is cornprised of several major geological units: a shield region, four

platfon regions, three orogens, and three continental shelves. (Geology and

Canada. GSC, 1990). These regions are shown in Fig. 5.1 and narrated in table

5.1 :

Fig 5.1: Main Geological regions of Canada. Scanned from: Geology and Canada, GSC, 1990.

rable-Sei The Four Main GEOLOGICAL UNIT

2. PLATFORMS

Geological Units of Canada LOCATION

Underlies about half the total area of the country.

- -- - --

O lnterior Plattom of Canada between

St. Lawrence Platform

Canadian Shield and CordiIleta. Arctic platforni underlies most of the Arctic Islands,

The St. Lawrence Platform is the southem part of the Shield from Lake Huron to Quebec City, encept for a srnaIl area of the

Hudson Bay and Hudson Bay Lowland between Churchill and Moosonee,

Hudson Platform

ROCKS AND STRUCTURE

hi el-d called the Frontenac b is . Hudson platform underlies most of

Rocks of Precambrian ages exposed or covered only by overburden. Shield fairiy stable since the end of Precarnbrian tirne, except foc Uplifting in late Tertiary time, changes in elevation after the glaciation of the Pleistocene period, faulting along the southem border and near Boothia Peninsula at different times after the end of the Precarnbrian.

- --

Undisturbed or gently flexed sedimentary strata overlie a basement of Precambrian rocks. Contains flat strata, rnainly Ordovician and Silurian limestone, dolomite, and shaly dolomite. Strata of Cambrian, Devonian, and Tertiary ages are also present locally.

Areas towards southwest and northeast of the Axis are underlain by gently dipping beds of lirnestone, dolomite, sandstone, and shale of Cambrian, Ordovician, Siludan, Devonian, and Mississippian ages,

The platform is underlain by Ordovician, Silurian, and Devonian strata of lirnestone and dolomite, Large deposits of gypsum in the Devonian succession and lignite deposits occur in Mesozoic beds.

3, OROCENS

Table 5.1 Continued.. . . .

Apptilnchinn Orogcn

GEOLOGICAL UNIT

Cordillcrnn Orogcn Western Cordilera Eastern Cordillera

'I'hc Appiiliichiiin Oriigcn inclutlcs 11ic pari ol' Quchcc lying souili of' tfic Si. lmwrcncc Hivcr id casi of u linc hciwccn l~icrkç Chiiniplain antJ Quehcc City, nnd nll of Ncw Brunswick, Navü Scoiiii, Prince FAwiird Isliind, and ihc lslnnd of Ncwfoundlnnd. The Canndian CordiIlcri1 is pri of a widc hclt of high mauninins and plüicrru cxtcnding nlong i hc wcslcrn sidcs of South and Norih Anicrica. Thc most northcrly scgmcnt of North Amcriciin Cdillcrii includcs r i i l of Ciiniitlri and A t i isli~i.

LOCAflON

'I'hc fnnuiiiiin Orogcii cnfcnds ncross IIIUL'~ of ihc Quccn Elizithc~ti Isliinds ;rnd ntirihcrniiicisr Grccnt;ind. ln !lie nortlicrisi dircciicin, ilic region cxicnds h i i r Princc I'itirick lsliind id iiicludcs iiII ol' Axel Hcihcrg IsliinJ iiiitl iiiiidi (il' lillcsiiicrc I~l i i i i t l .

- ROCKS AND STRUCTURE

A great fault separates Appalachian Orogen and St. Lawrence Platform. The fault forms a sweeping cuwe ta the south shore of the lower St, Lawrence as a result of thrusts that occurred during the Ordovician and Devonian penods.

The segment that les in 6.C and Alberta is divided in two main geological and structural provinces by a long straight valley called the Rocky Mountain Trench. This trench dies out at about 60' latitude. The western parl of trench is underbin rnalnly by plutonic, volcanic, and metamorphic rocks. The eastem part of trench has Rocky mountains and the Foothill betts fomed of sedimentary strat-a cast into great folds and faul blocks. From 60' latitude to the south of Arctic Coast, there is a boundary between eastern and western Cordillera. The western part of the Cordilleran Orogen is the site of a series of geosynclines of a kind in which volcanic and plutonic rocks as well as sediments are fomed. The rnountains and foothills of the Eastern Cordillera were carved by the erosion of great thickness of sediments that were deposited in geosynclines.

'The sirrii;i arc niiiinly scdiincnt;irp tiui inçludc sotiic nicininorphic and volc;iniC rocks.

Table 5.1 Continued.. . . . GEOLOGICAL UNIT LOCATION ROCKS AND STRUCTURE

IXONTINENTALSHBLVFS Extending off Pacific and Atlantic Rock conditions more or less similar to those on neahy coasts. mainlands are present in several places beneath the shelves

and, locally, extensions of faults and other structures have been 1 1 1 t raced. 1 Saurcc: C;calogy nnd Canada, Nniurd Resourccs Cunndii, GSC.

5.2.2 SURFACE MATERIALS

The surface materials of Canada, overlying the broad geological units

summarized in 5.2.1, are displayed in Figures 5.2 - 5.7. These maps were

produced by modifying the digital release of the map titled "Surficial Materials of

Canada, digital release, Map 1880 A , compiled by Dr. R.J. Fulton. Geological

Suwey of Canada. This rnap shows the surficial materials at 1 :5 000 000 scale.

The broad genetic categories are: alluvial, lacustrine, marine, glacial and

bedrock, each of which are further subdivided according to texture, thickness,

and landform. On this basis, the map shows 24 classes of surface material. In

this study, the original classes were simplified to 13 classes of surface rnaterials.

The modifications were done in a GIS software package (Arcview, v 3.0) under

the supervision of Dan Patterson, Carleton University. After reclassifying the

surficial geology, the total rnap area was subdivided into four regions: Eastern

Canada, Mid Canada, South-western Canada and North-western Canada; to

enhance the detail of the presentation. Reclassifying the 13 classes in just 4

classes made an overview map. The four classes are: Glaciers, rock, soil, water.

The purpose for the oveiview reclassification was to show not only the very

broad surface geology of the study area, but also to show the location of the

earthquake recording stations and the earthquake events studied in this project.

The classification schemes are shown in Table 5.2. Figure 5.1 shows the

overview classifications and the locations of study earthquakes and recording

stations. Figures 5.2 - 5.7 show the classifications in more detail by region. and

include the H N results at frequencies of 1-hz and 5-hz (as multiplicative factors).

Table 5.2: Reclassitication Scheme For The Surficial Materials Of Canada

MAP 1880A SURFACE CLASSES

L

Alluvial Deposits

Marine Mud

Marine Sand

, RECLASSIFICATION

NAME

Glaciers

L

Lacustrine Mud

Lacustrine Sand

DEFINED CLASSES

(13 CLASS- ES) Glaciers

L

Eolian Deposits

OVERVIEW CLASSES (4 CLASS- ES) Glaciers

SYM- BOL

1

Soi1

Soil

Soi1

mL

sL

L

Organic Deposits

1 B'ockS 1 1 metamorphic substrate & cemented 1 from crystalline bedrock. medium grade

COMPOSITION

Ice & rninor morainal debris

Alluvial

Marine

Marine

1

A

mM

SM

E

I

Colluvial

1

Stratified silt, sand, clay & gravel; floodplain, delta, 8 fan deposits; in places overlies & includes galociofluvial deposits. Fluid silty ciay and clayey silt; deposited as quiet water sediments.

Sand & locally gravel; deposited as sheet sands, lags, and beaches,

Fluid silty clay and clayey silt; deposited as quiet water sediments.

Sand and localty gravel; deposited as sheet sands, lags, 8 beaches.

O

Sand & minor silt; dunes, blowouts, & undulating plains; in most places overlies deltaic sediments, coarse lacustrine

bC

Colluvial Rubble

Colluvial Fines

1 1 1 lithified s-andstone & conglornerate 1 1 1

Lacustrine

Lacustrine

sediments, or glaciofluvial deposits. Peat, muck and minor inorganic sediments; large bog, fen, & swamp areas where orgariic fil1 masks underlying

Colluvial Sand

Soil

Soi1

I

surficial material; generally > 2m thick. Block. & rubbte with sand and silt derived

rC

fC

Eolian

I

SC

Fine grained (Glacio)

Soil

Organic

Colluvial

sandstone. Rubble i% silt; derived from carbonate & consolidated fine clastic sedimentary

. rock substrate. Silt, clay 8 fine sand; derived from substrate weakly consolidated shale &

, Lacustnne Coarse grained (G lacio)

So il

Soil

siltstone substrate. 1 Sand & gravel; derived from poorly 1 Colluvial

fL

Colluvial

Colluvial

Soil

CL

Soil

Soil

substrate. Silt & clay, locally containing Stones; deposited as quiet water sediments

Sand, silt, 8 gravel; deposited as deltas, sheet sands, 8 lag deposits.

Lacustrine Soil

Lacustrine Sail

Table 5.2 continued.. ,,.,

MAP 1880A SURFACE CLASSES

NAME 1 SYM- 1 COMPOSITION

Fine grained fM Oominantly silt 8i clay, locally containing Marine 1 / stoner; deporited as quiet water 1

BOL

, RECLASSIFICATION

Marine

Marine

OEFINEO CLASSES

(13 CLASS- ES)

OVERVIEW CLASSES (4 CLASS- ES)

sedirnents. Sand 8 gravel; deposited as sheet sands, deltas, 8 extensive flights of beaches.

Sand, gravet, 8 pockets of finer sediment; thin ta discontinuous sediment veneer & residual lag developed during marine submergence; includes areas of

Coarse grained (G lacio) Marine Lag (Glacio) Marine

CM

Mv

1

Glaciofluvial P Iain Glaciofluvial Complex

Soil

1 washed till & rock. Gp 1 Sand & gravel; deposited as outwash

Till Blanket

Soil

Glaciofluvial

Gx

Soil

Tb

Soil sheets, vdley trains,& terrace deposits Sand & gravel 8 locally diamicton; undifferentiated ice contact stratified drift

Soil Glaciofluvial

& outwash: locally includes till & rock. Thick & continuous till. 1 Soil Till Blanket

' Till Veneer

Quaternary Volcanics

Alpine Complexes

C I 1 1 1

Source: Digital release, Surficial Materials of Canada, Map 1880 A (1 995)

. Uridivided

Notes:

1. Soil is referred to on maps as "Surface Materials".

1

TV

V

Ra

R

2. Eolian, Lacustrine, and Marine materials can be differentiated based on

Till Veneer

Quatetnary Volcanics

Rock

Thiri 8 discontinuous till; may include extensive areas of rock outcrop. Consolidated lava, breccia & tephra; dominantly basaitic & andesitic in composition; includes flows, volcanic piles, & cinder cones. Rock, colluviam, 8i till; rock 8 Quaternary deposits cornplex in an area, character-

transpoitation mechanism and composition of the sediments. These can be

Rock

Rock

Rock

ized by alpine & glacial landforms. Rock with minor Quaternary deposits.

defined as:

Eolian materials are derived by wind erosion from other soils or barren lands.

Rock Rock

Lacustrine sediments are generally associated with activities of glaciers or

glacial meH waters. They Vary in texture and mineralogy. Generally they are

fine textured and well sorted.

Marine sediments commonly contain glauconite or marine diatoms. (Fanning

and Fanning, 1989)

5.3 ANALYSIS OF HN IN LlGHT OF GEOLOGY OF RECORDINO STATION

The recording stations of the Canadian National Seismographic Network (CNSN)

are located, to the extent possible, on rock sites or rock outcrops. Figures 5.3 - 5.7 show the class that is most dominant near the recording station, although the

station rnight actually be located on a rock outcrop. The dominant site conditions

at the recording sites were compared to the HN ratios obtained at frequencies of

1 -hz and 5-hz. Two types of classifications were adopted for this purpose:

(i) Data sorted (in ascending order) at 1-hz were subdivided into three classes

with H N c 1, WV = 1 - 1.2, and H N > 1.2, respectively. (ii) Data sorted (in

ascending order) at 5-hz were subdivided into three classes with H N c 1.2,

HN = 1.2 - 1.4, and HN > 1.4, respectively. Sections 5.3.1 and 5.3.2 show three

tables with the results of the analysis. HN ratios are presented as multiplicative

factors (Le. p& in log units).

5.3.1 H N RATIOS AT 1-hz

Table 5.3: WV for i hz; WV < 1 (class A-ta)

Station A54 A64 INK WALA A21 MBC A16 YKW4

Station LMQ PMB DRCN BBB MOBC PGC RES GAC ULM PNT YKW3 SCH LMN A61 DAWY A l 1 WHY

Geology Till Blanket Till Blanket Till Veneer Rock Marine Colluvial Manne Till Veneer

Rock Till Veneer Rock Colluvial Marine Colluvial Tilt Veneer Rock TiH Veneer Till Veneer Till Veneer Rock Marine Colluvial Marine Till Blanket

ed Geology Thick & continuous lill, Thick 1L continuous tili. Thin 8 discontinuous till. May contain extensie areas of rock outcrop Alpine Complexes Dominantly silt & clay, locally containing stones. Sand & grawl deried from poorly lithified sandstone 8 conglornerate Dominantly silt 8 clay, locally containing stones. Thin & discontinuous till. May contain extensive areas of rock outcrop

ed Geology Thin & discontinuous tilt. May contain extensive areas of rock outcrop Alpine Complexes Thin 8. discontinuous till. May contain extensive areas of rock outcrop Rock with minor Quatemary deposits Block & rubble with sand and silt derived from ctystalline bedrodc. Sand, gravel 8 pockets of finer sediments; includes washeâ till& rock. Rubble & silt, derived from carbonate & consolidated fine clastic sed. rock. Thin & discontinuous till. May contain extensive areas of rock outcrop Rock with minor Quatemary deposits Thin & discontinuous till. May contain extensive areas of rock outcrop Thin & discontinuous till. May contain extensive areas of rock outcrop Thin & discontinuous till. May contain extensive areas of rock outcrop Rock with rninor Quatemary deposits Dominantly silt & clay, locally containing stones. Block & rubble with sand and silt derived from crystalline bedrock. Sand & gravel; deposited as sheet sands, deltas & extensive beaches, Thick & continuous till,

Table 5.5: W tor 1 hz; HN > 1.3 (c las A4c)

YKW2 YKWI FCC

Geology Till Blanket

5 hz 1.71

Station DLBC

FR8 SAD0 €DM

ûetailed Geology Tb llhick & continuous till.

1.31 1,37 1.41

1 hz 1.30

1.42 1.49 3,84

90% C,I at 1 hz 1.23 - 1.38 1 .O7 - 1.61 1.11 - 1.67 1.15 - 1.74 1.16 - 1.74 1.20 - 1.86 2.90 - 5.08

1.29 2 0.94 1.25 1.26 1.89

Till Veneer Tilt Veneer Marine Till Blanket Rock Ti11 Blanket

TV TV CM

Thin & discontinuous till. May contain extensiw areas of rock outcrop 7hin 8, discontinuous till. May contain extensiw areas of rock outcrop Sand & grawl; deposited as sheet sands, deltas & extensiw haches.

Tb R Tb

lhick & continuous till. Rock with minor Quaternary deposits lhick & continuous till.

Frorn the above tables, it is obseived that at 1-hz, the WV ratios are generally

near unity. However, for station EDM the 1 -hz HN ratio attains a value of nearly

a factor of 4, suggesting significant site response. The HN ratio at EDM drops

down to about a factor of 2 at 5-hz. One possible reason for this type of

response could be a topographic amplification effect. The elevation of the station

recorded by GSC is 730m. From the topographic rnap of Bittern Lake (Sheet 83

W3, Dept. of Energy mines and resources, 1974), the topography surrounding

the station was checked. It was obsewed that the station is located on the flank

of a river valley. This particular area is very steep compared to a gentle relief for

the rest of the area. (The elevation changes about 30m over a distance of 1 km

in the vicinity of EDM). Hence this information points to a topographic effect. For

the rest of the stations, there is not a clear pattern associating the 1 -hz WV ratios

to the geological conditions. The mean H N values at 1-hz for classes A-la, A-

I b, A- l c are 0.85, 1 -14 and 1.73 respectively.

Table 5.8: W for 5 hz; W > 1.4 (class A&)

DAWY

ULM

5-hz 1,44 1,48 1.71 1.71 1.72 1.88 1.89 2.37 3.18

undefined

i 1.39 - 1.50 i ~ a n n e - CM ISand & gttwl; deposited as sheet sands, deltas 8 extensiw beaches. Rock Till Blanket Manne Manne Collu\cial Till Blanket ColluHal

Rock with minor Quatemary deposits ïhick & continuous till. Dominantly silt & clay, locally containing stones, Sand, graw1 & pockets of finer sediments; includes washed till & rock. Block & nibble with sand and silt deried from crystalline bedrock. ïhick & continuous till. Block & rubble with sand and silt derited from crystalline bedrock.

] 3.10 - 3.27 l ~ a r i n e IfM lDominantly silt & clay. locally containing Stones. NIA Rock R Rock with minor Quaternary deposits

At the frequency of 5-hz, the following observations were made: of a total of 32

stations, 9 stations show WV ratio less than 1.2, 13 stations show amplifications

between 1.2 and 1.4, and 9 show an amplification higher than 1.4. Station ULM

has an undefined value of HN at 5-hz (due to insufficient observations with

S/N 1 2). The average amplifications for classes A-5a, A-5b, A-5c are 1.06, 1.30

and 1.93 respectively. At 5-hz, the correlation with geology becomes more

obvious than at 1-hz. Stations with low to moderate amplifications are mostly

located in rocks or rock-like environments. Stations that show amplifications of

more than 1.4 are mostly located on marine, thick till or colluvial materials. The

maximum amplification is about a factor of 3 for the station A61 (Charlevoix

array). It is surrounded by Marine material composed of silt and clay with stones.

An interesting setting of this station is that it is installed in between the stations

A64, LMQ and A54. These three stations are installed where the surrounding

material is mostly Till Blanket and the amplification factors are 1.3, 1.3 and 1.2

respectively. So the amplification for A61 might have been strongly influenced by

the local geological conditions (marine materials).

F SI, 5.2 EARTHQUAKES AND RECORDINO STATIONS WlTH SURFACE OEOLOOY r

.-

P+

\

/

/

\

/ \

l 1 I t

-120° 1 I 1

30' -1 IO0 -10Oo -90° -80' 30' I -70' 60'

A Strüona LEGEND

Eiraiquikm 2500 O 2.5-2.8

2500 Kilomotm

3-3.4

Projection Information: N Projection: Lamkrt Confornial Conic A Central Merklbn: -85 Ref. Latitude: 49 Standard Parallela: 49 N. 77 N M.p Ret Surlidsl Materiab of

Canada, Map i88O A

FIG 5-3 SURFACE GEOLOOY AND MEAN HN VALUES FOR NW4ANAOA

A N W ~ ~ M Sbloni LEGEND surlrce Ooabgy

Alluvial C o l ~ l

400 O 400 800 Kilom Eoüan I O~~CI.~B Projection l nfonna tio- o ~ ~ ~ N ~ I Projection: Lambert Conformal Conic lmcrrwm Math8 Central Meridian: 95 W Otglnk Qwt. Volunien

Ref. Latitude 49 N k i t Standard Parallele: 40 N, 77 N TM Dlnkot r n ~ Vanoor Map Ref: Surficial Materials of W8bt Canada, Mao 1880 A

F Ici. 5$ SURFACE OEOLOGY AND MEAN HN VALUES FOR SW-CANADA 1 /

1 - --

A 6w-Canada 6trüunr Gurlrcm Omolo~

LEGEND Uluvtrl

100 O 100 200 Kilometeri Colluvial Eolbn Projection Information: -

Projection: Lambert Conformal Conic Okcbfiuvbl

'cuaha Central Meridian: 05 W M8th0

49 N rrrt ioa. Oaeht riveht

Orginb Qu i t Volernicc

Ref. Latitude: ROC^ Standard Parallels: 49 N, 77 N cm 1-11 l . ls l ia Blinirat cm 1-02 0.94 n v a n a a r Map Ref: Surficial Materials of Ec Witmr 1-09 1 . 72 Canada. Mao 1880 A am 1-04 7 -06

69

~14.545 SURFACE OEOLOOY AND M W H N VALUES FOR MlDtANAbA

1 1 i I

-llSO L

-t IO0 1

-lOSO 1

-1Oo0 9s0

LEGEND 600 Kilometers

FIG.5-5 SURFACE OEOLOGY AND M U N H N VALUES FOR EASTERN CANADA

. -

LEGEND

Projection Information: Projection: Lambert Conforma1 Conic Central Meridian: 95 W

Standard Paralklo: 40 N. 77 N Map Ref: Surlicial Materials of

Canada. Map 1880 A a1

F (5.597 SURFACE GEOLOGY MAP FOR CHARLEVOIX AREA

A Chithvoix 6btbnr

200 Kilometers

O~C~I IWI ,~ Projection Information : Projection: Lambert Conformel Conic Central Meridian: Q5 W Ref. Latitude: 48 N

m"n*t Standard Parallela: 49 N, 77 N Map Ret Surficial Materials of

Canada. Man 1880 A fi? i

CHAPTER 6

CONCLUSIONS

6.1 INTRODUCTION

This chapter presents the conclusions of the study. The conclusions are based

on a possible correlation with geology and a comparison of results with previous

work. From the point of view of seismological proparties, a survey of previous

studies is presented and HN ratio results are cornpared in the light of past

research. From the geological point of view, the conclusions are based on the

analysis presented in chapter 5. The prospects for future work are explored with

reference to the work done in different parts of the world (an outline of which is

presented in chapter 2.)

6.2 SElSMOLOGlCAL PROPERTIES

It has been suggested that the observed HN ratios may be a measure of the

amplification of seismic ground motions due to their transit through the crustal or

near-suiface velocity gradient . In this section, I suivey studies pertaining to H N

and ground motion amplification, in eastem and western Canada. Tables 6.1 and

6.2 present a brief overview of the studies. After this review, the results obtained

from the current study will be compared with the findings of the previous studies.

Table 6.1: Site Effect Studies for Western Canada

STUOY

Atkinson & Boore 1 997

Boore & Joyner, 1997

FOCUS OF STUDY

To develop preliminary ground motion relations for the Cascadia region for rock sites.

To present average velocity versus depth and amplification versus frequency for rock sites in Eastern & Western North America.

The average WV is larger at high frequencies than the ratio obtained by Atkinson 1993 (see table 6.2) for eastem hard rock sites, WCTN sites have lower near surface velocities than ECTN sites. (For example 1.5 krnlsec vs. 2.8 km/sec.)

The average shear wave velocity for Western North ~merica' for the top 30 m is 620 mls. The amplifications of rock sites can be in excess of 3.5 at high frequencies. The combined effect of attenuation and amplification for rock sites peaks between about 2 and 5-hz with a maximum level of less than 1.8. At 1 -hz, the cornbined eff ect is a factor of 1.5

Atkinson & Cassidy , Feb., 2000

Table 6.2: Site Ef STUDV

Atkinson 1993

Boore 8 Joyner, 1997

Beresnev and Atkinson 1997

Ta present a new method ta estimate soi1 amplification using regional seisrnographic data for sites in Fraser Delta, B.C.

Table 6.1 continued, , , , Fraser Delta soils amplify weak motions three to five times for frequencies of 0.3 to 4-hz. Motions are de- amplified for f > 10-hz. The HN ratio appears to be correlated with the site amplification. Rock sites in western region show similar WV charactenstics, except sites located on batholithic rocks (BBB, PMB, PNT). These sites have higher shear wave velocities and lower H I ' .

!ct Studies for Eastern Canada

To present average velocity versus depth and amplification versus frequency for rock sites in Eastern & Western North America.

FOCUS OF STUDY

Determine HN ratio for hard rock sites in ENA.

Obtain information about pre- dominant site effects frorn shear wave refraction suwey in Ontario.

FlNDlNGS

HN ratio for the hard rock ECTN (Eastern Canada Telemetered Network) sites increases with frequency frorn a value of 1.1 at 1 hz to 1.5 at 10-hz.

The amplification factors are less than 1.2 on veiy hard rock sites of Eastern North America. The average shear wave velocity for top 30 m is 2.88 krn/s,

The amplification for an average hard rock site in Ontario is about a factor of 1.3. For south and southeast Ontario, velocity structure was detemined to a depth of about 70m. Near surface S- wave velocities of hard rock sites range from 1.7 to 3.1 krn/s, the average being 2.6 km/s. Surveyed Eastern seismograph stations have minimal site effects.

6.3 RESULTS OF THE STUDY

In this section the results of the current study will be presented for eastem and

western Canada and will be compared with the findings of the previous studies.

Tables 6.3 - 6.6 present the mean H N values and the range indicated by the

90% confidence limits on the mean. It is assumed in these cornparisons that the

H N ratio is a rneasure of site amplification.

Results for SW-Canada:

Table 6.3: Amplification Factors for SW-Canada

- - - 1 I - -

Average amplification at 1 hz: 1 .O7 Standard deviation: +,- 0.05 Average amplification at 5 hz: 1.22 Standard deviation: +,- 0.29

PNT PMB PGC BBB

Table 6.4: Amplification Factors for NW-Canada

Mean HN 1.14 1 -02 1 .O9 1 .O4

90% C.1 Range 1.63 - 1.78 1.29 - 1.37 1.79 - 1.98 0.79 - 2.33 0.99 - t .O7 2.30 - 2.45 1.02 - 1.13

L

0.93 - 1.13 1.04 - 1.13 0.99 - 1 .O9

Station

v

DLBC

Standard deviation: +,- 0-1 6 Standard deviation: +,- 0.45

9Ooh C.1 Range 1 .O6 - 1.25

90% C.1 Range 1 .O7 - 1.21

WHY MOBC MBC INK DAWY RES

Mean WV 1-15 0.94 1.72 1 .O6

1 hz 1 5 hz

0.77 - t .le 1.59 - 1.86 1.02 - 1.10

Mean HN 1.30

Average amplification at 1 hz: Average amplification at 5 hz:

1.26 1 .O8 0.93 0.83 1.23 1.11

90% C.1 RangefMean WV '

1.23-1.38 1 1.71 "

1.20 - 1 -32 1.01 - 1.16 0.66 - 1.32 0.78 - 0.90 1.16 - 1.31 1 .O0 - 1.22

The study of Boore & Joyner, 1997 proposes that the combined effect of

amplification and attenuation at 1-hz is 1.5 and that between 2 and 5-hz it is less

than a factor of 1.5, for generic western rock sites. The results of this study

suggest that, if amplification is represented by HN, the amplification levels for

SW-Canada are 1.1 and 1.2 for 1-hz and 5-hz respectively. For NW-Canada, the

amplification levels are 1.1 and 1.5 for 1-hz and 5412, respectively. These ratios

are generally consistent with the amplifications presented by Boore and Joyner

(1997). Atkinson & Cassidy, (2000) show that the HA/ ratios for stations in SW-

6.C are consistent with theoretical estimates of site amplification based on

irnpedance changes in the near-surface materials.

Table 6.5: AmpiHication Factors for Eartem Canada

Stations - FR6 GAC SAD0 DRLN SCH LMQ LMN A l 1 A1 6 A21 A54 A61 A64

Average at 1 k 1 .O9 SbnQrd deviation: +,- 0.24 Average at 5 hz 1.48 SbnQrd deviation: +,- 0.51

The results of this study for Eastern Canada are very consistent with the results

of four studies outlined in Table 6.2. The amplification factor increases from 1.1

at 1-hz to 1.5 for higher frequencies. Outside the Charlevoix region, most stations

have a 5-hz WV ratio of 1.3 to 1.4. Based on impedance effects discussed in

Chapter 2 ([(pl p2) 1 (pl PI)]**^), this would imply typical near-surface shear-wave

velocities of 1.9 to 2.2 kmls (for deep crustal velocity of 3.8 kmls), consistent with

the refraction results of Beresnev and Atkinson (1 997).

Tabk 6.6: Amplification factors for Mid-Canada

YKW1 1.36 1.11 - 1.67 YKW2 1.31 1 ,O7 - 1.61 YKW3 1 ,21 1.47 * 1 .O0 YKW4 0.81 ' N/A FCC 1.41 1.15 - 1.74 €DM 3.84 2.90 - 5.08 ULM 1 .l4 0.83 - 1.55

Average Amplifications at t hz: Average Amplifications at 5 hz:

1.49 Standard deviation: +,- 0.91 1.26 Standard deviation: +,- 0.29

' Value for Mean extrapolated from data.

Average except EDM at 1 hz: 1 .16 Standard deviation: +,- 0.22 Average except €DM and ULM at 5 hz: 1 .t 6 Standard deviation: +,- 0.1 4

The average amplification factors for midacanada at 1-hz are biased by a high

response of €DM. The rest of the stations do no? show a high amplification level

at 1-hz. At a frequency of 5-hz, the average amplification factor for midCanada

stations is 1.26, which is lower than the response of Eastern and Western

stations. (1.49 and 1.53 respectively at 5-hz.) If the response of EDM is excluded

from the average, then the amplification levels at both 1 -hz and 5-hz are 1 .16.

The low H N ratios in midocanada imply high near-surface shear-wave velocities,

which is consistent with the highly-competent Canadian Shield rock conditions.

We compare the results of rnean HN ratios, considering the standard deviation

and 90% confidence interval of the average for each region. It is obsetved that

the average H N for typical rock sites is 1.1 IO.l at 1 hz, and it is in the range of

1.2 to 1.5 at 5 hz. This trend is same al1 over the country. Table 6.7 shows these

observations.

Table 6.7: Cornparison of Mean HN, Standard Deviation and 90% C.1 at l-hz and 5-hz

Reg ion Values et 1-hz: Values at 5-hz:

6.4 FUTURE PROSPECTS AND SUMMARY OF CONCLUSIONS

Based on the survey presented in Chapter 2, this work can be further extended in

several areas. For exarnple, one of the most active seismic regions of Canada is

the Charlevoix zone. It has seven closely-located three-component recording

stations on rock to monitor the seismic activity of the region. Following Duval et al

(1 995) site amplification maps of the Charlevoix seismic zone can be produced if

further stations are placed on typical soi1 sites in the area. Duval et al (1995)

produced site amplification maps in Nice, France based on H N ratio curves

obtained for that region. From these H N ratio curves, they chose one value each

for the frequency (of maximum amplitude) and maximum amplitude. They then

proceeded with interpolating these values to produce the site amplification maps.

They also found VIat these maps agreed reasonably well with the geological

I

. SW-Canada _NW-Canada Eastern Canada Mid-Canada Mid-Canada (except

Mean 1.07 1.11 1.09 1.19 1-16

S.D 0.05 0.16 0.24 0.91 0.22

90°hCI 0.04 0.09 0.07

. 0.53 0.14

Mean 1.22 1.54 1.48 1.26 1 .16

S.D 0.29

90%CI 0.24

0.45 0.51 0.29 0.1 4

0.28 l

0.23 0.18 0.09

conditions of the area. A similar study could be perfomied in Charlevoix. A further

enhancernent of the study could be to correlate WV with rock type (e.g. granite,

etc) or geological history. In this study, HN seems sirnilar for various regions at

most stations. Therefore, shear wave velocity is probably more important rather

than the rock type.

Many parts of Canada have relatively low seismicity. For such areas, Lermo and

Chavez-Garcia (1 994) suggest that micro-tremor measurements can

complement other site effect studies. Since the HN ratio technique is originally

proposed for micro-trernor recordings, it can be usefully applied in low-seismicity

regions to obtain information about the site effects. Once this information is

obtained, it can especially be used in urban areas. For example, Lachet and Bard

(1 994) find that the knowledge of the resonance frequency of soi1 can be used to

identify the kinds of buildings most prone to damage.

In site effect studies, the most popular technique used is the standard spectral

ratio technique. In this technique, site response of soi1 sites is determined relative

to a nearby hard rock site. Comparing the standard spectral ratio technique with

the H N ratio technique. Theodulidis et al (1996) find that there is a difference in

amplitude between the WV ratio and the standard spectral ratio. In this study, we

have obtained an estirnate of amplifications using the H N ratio method. For

ragions where accurate information of site response is required, calculating the

response by standard spectral ratio technique as well can refine the results of

this study.

Some of the important applications of this work are:

H N ratio can be used as a simple estimate of site amplification.

HN ratio can be used as a measure of regional variability of crustal amp-

lification effects through the velocity gradient.

HN can be used to estimate the horizontal component for the many older

seismograph recordings for which only the vertical component of motion

was measured.

Overall, I conclude:

The H N ratios are broadly consistent with typical amplification values

suggested for Noith American crust.

The results of the study are consistent with the results of previous studies.

For Western North America (particularly California), Boore and Joyner

(1 997) suggested that the combined effect of amplification and attenuation

for frequencies between 2 and 5-hz is less than a factor 1 S. The results of

this study indicate amplification levels to be 1.2 and 1.5 at 5-hz for south-

western and northwestem Canada respectively. For Eastern Canada,

Atkinson (1993) finds that W ratio increases with frequency from 1.1 at

1 -hz to 1.5 at 10-hz. Boore and Joyner (1 997) suggest that amplification

factors are less than 1.2 on very hard rock sites of Eastern North America.

The findings of this study indicate that HN ratio at 1 -hz is 1.1 and that at

5-hz is 1 .S. For the hard rock stations of eastem Canada (DRLN, A54,

SADO, A64) the amplification is indeed of the order of 1.2 at 5-hz.

A correlation exists between WV ratios at 5-hz and the general geology of

the recording stations. Am plif ications based on H N ratio are gene rally

hig h where the local geological conditions indicate relatively soft marine

rock conditions. For erample, the amplification factors inferred from H N

ratios are between 0.9 - 1.2 for bard rock (or hard rock outcrop) sites,

while for sites where marine materials predorninate, H N ratios Vary

between 1.4 to as high as 3.2.

At 1 -hz, the amplification for hard rock stations in al1 regions of Canada is

low, approximately 1.1 f 0.1 . At 5-hz the H N ratio is in the range from 1.2

- 1.5 on average.

APPENDIX: TABULATED RESULTS

Tabulated Statistics* for Station: A l 1

Frequency I log units

Standard Deviation

0.08 0.27 0.08 0.1 1 0.07 0.22 0.1 2 0.1 3 0.1 6 0.1 9 0.1 6 0.1 8 0.1 3 0.1 1 0.1 1 0.1 1 0.08 0.08 0.1 0 0.1 0 0.09 0.08 0.10 0.1 0

BO% Confidence Intewal

Tabulated Statirtics* for Station: A16

Frequency 'AH statistics given

Mean HN I I

h

1 log units Standard 00% Confidence

Interval

fabulated Statistics* for Station: A21

Ftequency Al1 statistics given in log units

Mean W Standard Deviation

Ott 8 0.00 0.07 0.08 0.14 0.24 0.18 0.08 0.1 8 0.1 2 0.14 0.14 0.17 0.1 1 0 .O9 0.1 3 0.1 1 0.1 2 0.1 1 0.08 0.06 0.09 0.07 0.05

BO% Confidence

Tabulated Statistics* for Station: A54

Frequency AH statistics aiven in Ion units

Deviation 30% Confidence

w

Mean W - Standard

111

-

Tabulated Statisttcs' for Station: A61

Frequency Deviation

0.52

'Al1 statistics given in log units BO% Confidence

Interval 0.49 0.1 6 0.1 2 0.00 0.00 0.1 O 0.1 5 0.1 8 0.07 0,09 0.07 0.04 0.02 0.02 0.02

- 0.02 0.01 0.01 0-01 0*02 0.03 0.03 0.03 0.02

Mean W Standard

Tabulated Statistics* for Station: A64

Ftequency 'AI1 statistics given

I I

-

Deviation 0.1 6

90% Confidence

Tabulated Statistics* for Station: BBB

Frequency 'AI1 statistics given

Mean W I I

-

1 log units Standard Devfation

90% Confidence

Tabulated Statistics* for Station: DAWY

Frequency Deviation

0.48

'Al1 statistics given in log units 90% Confidence Mean HN

Intewal 0.1 8

Standard

Tabulated Statistics* for Station: DLBC

90% Confidence

Tabulated Statistics* for Station: DRLN

Frequency i log units

Standard Deviation

0.00

90% Confidence ln terval

0.00 0,OO 0.1 7 0.08 0.00 0.36 0.05 0-21 0.09 0.16 0.06 0-07 0.05 0.06 O .O4 0-03 0.04 0 .O4 0.03 0.03 0.03 0.05 0 .O5 O .O0

Tabulated Statistics* for Station: €DM

Frequency 1 loq units

Standard Deviation

0.27

90% Confidence lnterval

Tabulated Statistics* for Station: FCC

Frequency 'Al1 statistics given

Mean HN I I

A

Deviation 0.00 0.00 0.00 0.05 0.00 0.26 0.23 0.1 7 0.1 1 0.1 9 0.1 2 0.1 8 0.21 0.1 5 0.09 0.07 0.09 0.1 4 0.1 4 0.00 0.00 0.1 9 0.04 0.00

90% Confidence

Tabutated Statktics* for Station: FR0

Frequency I log units

Standard 00% Confidence

Tabulated Statbticrg for Station: GAC

Frequency Devfation

0.00 0.00 0.1 1 0.09 0.18 0.30 0.20 0.1 9 0.07 0.1 2 0.20 0.18 0.1 7 0.1 2 0-1 4 0.1 2 0.1 2 0.1 3 0.1 4 0.1 1 0,13 0.1 3 0.14 0.1 1

'Ali statistics given in log units 90% Confidence

Intewal 0.00 0.00 0.1 3 0.1 1 0.1 7 0.1 5 0.1 9 0.13 0.05 0.06 0.1 1 0.09 O .O8 0.05 0 .O4 0.03 0.02 0.02 0.03 0.02 0.03 0.03 0.03 O .O6

Mean H# Standard

Tabulated Statistlcs4 for Station: INK

Ftequency i log units

Standard Deviation

0.1 8

90% Confidence

Tabulated Statistici* for Station: LMN

Frequency i log units

Standard Deviation

0 .O0

80% Confidence

Tabulated Statbtlcs* for Station: LMQ

Frequency 1 log units

Standard Deviation

0.02

90% Confidence

Tabulated Statlsticr* for Station: MEC

Frequency AI[ statistics aiven in loa units

Deviation

w - Mean HN Standard

1 m

iI

90% Confidence lntewal

Tabulated Statistics* for Station: MOBC

Frequency Oeviat ion

0.22

90% Confidence lntewal

'All statistics given in log units 5 Mean HN Standard

I I

Tabulated Statistics* for Station: PMB

Frequenc y Deviation

0.33

'AH statistics given in log units i, 90% Confidence

lntewal 0.08 0.07 0.08 0.06 0.06 0.05 0.05 0.04 0.04 0.04 0.04 0.04 0.05 0.05 0.05 0.06 0.06 0.09 0.14 0.1 1 0.1 1 0,11 0.1 2 0.13

Mean HN Standard

Tabulated Statistics* for Station: PGC

Frequency i log units

Standard Deviation

0.1 8

90% Confidence

Tabulated Statistics* for Station: PNT

Frequency 1 log units

Standard

Tabulated Statistics* for Station: RES

Frequency Deviation 0.00

'Al1 statistics given in log units 90% Confidence Mean H/V Standard

Tabulated Statisticr' tor Station SCH:

Ftequency I log units

Standard

I

QO% Confidence 'Al1 statistics given

Mean HN m

I

Intewal 0.00

Tabulated Statistics* for Station: SAD0

Frequency I log units

Standard 90% Confidence

Tabulated Statistics* for Station: ULM

Frequency Deviation

0.00

'Al1 statistics given in log units 00% Confidence Mean HN

Intewal 0.00

Standard

Frequency

Tabulated Statisticse for Station: WALA i log units

Standard Deviat ion

0.23

90% Confidence

Tabulated Statistics' for Station: WHY

Ftequency Msan HN I I

m

i log units Standard Deviation

0.20 0.1 4 0.1 5 0.1 7 0.1 9 0.1 7 0.1 9 0.1 4 0.1 6 0.1 4 0.1 5 0.1 4 0.1 4 0.13 0.1 2 0.1 1 0.1 2 0.1 2 0.1 1 0.1 0 0.1 O 0.1 0 0.10 0.21

90% Confidence lntewal

Tabulated Statistlcs* for Station: YKW1

Frequency 1 log units

Standard Deviation

0.1 2

Tabulated Statistlcr* for Station: YKW2

Frequency 'All statistics given

Mean HN I I

I

1 log units Standard 90% Confidence

Tabulated Statistics* for Station: YKW3

Frequency Deviation

0.00 0.1 3 0.25 0.23 0.23 0.23 0.1 8 0.20 0.1 7 0.1 9 O .23 0.1 4 0.1 9 0.1 7 0.1 4 0.1 4 0.1 O 0.1 O 0.08 0-08 0.02 0.00 0.00 0.00

'All statistics given in log units 90% Contidence Mean WV Standard

Tabulated Statistlcs* for Station: YKW4

Frequency Deviation

0.00

'All statistics given in log units 90% Contidence Mean W Standard

REFERENCES

Atkinson, G.M. (1993) Notes on ground motion parameters for

Eastern North America: Duration and H N ratio. Bull. Seisrn. Soc.

Am. 83,587-596.

Atkinson, G.M., and Boore. (1 997). Stochastic point source

modeling of ground motions in the Cascadia Region. Seism.

Res. Letters. 68, 74-85

Atkinson, G.M. (1 999). Lecture Serieç: Engineering Seismology.

Carleton University course 57.577, Ottawa

Atkinson, G.M., and J. Cassidy. (2000). lntegrated use of

seismograph and strong motion data to deterrnine soi1

amplification: Response of the Fraser DeHa to the Duvall and

Georgia Strait Earthquakes. Bull. Seism. Soc. Am. (In Press).

Beresnev, I.A., and G.M. Atkinson. (1 997) Shear-W ave velocity

suwey of seisrnographic sites in Eastern Canada: Calibration of

Empirical Regression method of estimating site response. Seism.

Res. Letters. 68,981 -987

Bonilla, L.B., J.H. Steidl, G.T. Lindley, A G . Tumarkin, and R.J.

Archuleta. (1 997). Site amplification in the San Fernando valley,

California: Variability of site-effect estimation using the S-Wave,

Coda, and WV methods. Bull. Seism. Soc. Am. 87.710-730

B o o ~ ~ , D.M., and W.B. Joyner. (1997). Site amplifications for

generic rock sites. Bull. Seism. Soc. Am. 87.327-341

Bour, M., D. Fouissac, P. Dominique, and C. Martin. (1 998). On

the use of micro-trernor recordings in seisrnic microzonation. Soil

Dynamics and Earthquake Engineering. 17,465-474

Castro, R. R e , M. Mucciarelli, F. Pacor, and C. Petrungaro. (1 997)

S-wave site response estimates using horizontal-to-vertical

spectral ratios. Bull. Seism. Soc. Am. 87, 256-260

Dobrin, M.B. (1 984). Introduction to Geophysical Prospecting . 3rd

Edition.

Duval, A., P. Bard, J. Méneroud, and S. Vidal. (1995). Mapping site

effects with micro-tremors. Proc. fl lntemational Conference on

Seismic Zonation, 3, Nice, France. 1 522-1 529

Fanning , D.S., and M .C.B. Fanning . (1 989) Soil-Morphology ,

genesis and classification. John Wiley and Sons.

Field, E.H., and K.H. Jacob. (1995). A cornparison and test of

various site-response estimation techniques, including three that

are not reference-site dependent. Bull. Seism. Soc. Am. 85.

1127-1 143

Fulton, R.J. (1 995). Surficial materials of Canada, Geological

Survey of Canada, Map 1880A, scale 1 : 5,000.000

Geli, L., P.-Y Bard, and B. Jullien. (1 988). The effect of topography

on earthquake ground motion: a review and new results. Bull.

Seism. Soc. Am. 78,42963

Geological Survey of Canada. (1990). Geology and Canada.

Natural Resources Canada.

Guteirrez, C., and S.K. Singh. (1992). A site 3 e c t study in

Acapulco, Guerrero, Mexico: Cornparison of results frorn strong-

motion and micro-tremor data, Bull. Seism. Soc. Am. 82, 642-

659

Kulhanek, Ota. (1990). Anatomy of Seismograms, Developments h

Solid €a r t h Geophysics. 1 8

Lachet, C., and P. Bard. (1994). Numerical and theoretical

investigations on the possibilities and limitations of Nakamura's

technique. J. Phy. Earth. 42,3779397

Lermo, J., and F.J. Chavez-Garcia. (1 993). Site effect evaluation

using spectral ratios with only one station, Bull. Seism. Soc. Am.

83,1574-1 594

Lermo, J., and F.J. Chavez-Garcia. (1 994). Are micro-tremors

useful in site response evaluation? , Bull. Seism. Soc. Am. 84.

1350-1 364

Nakamura, Y. (1 989). A rnethod for dynamic characteristics

estimation of subsurface using micro-tremor on ground surface,

OR RTRl30,25 - 33

Sheriff, RE., and L.P. Geldart. (1995). Exploration Seismology, Td

Edition.

Surveys and Mapping branch, Department of Energy, Mines and

Resources. (1974). Topographie map, Bittern Lake, Sheet 83

HI3, 2nd edition.

Tevez-Costa, P., L. Matias, and P.-V. Bard. (1996). Seismic

behaviour estimation of thin alluviam layers using micro-tremor

recordings. Soi/ Dynamics and Earfhquake Engineering. 15,201 - 209

Theodulius, N., ?.-Y. Bard, R. Archulata, and M. Bouchon, (1996).

Horizontal-to-vertical spectral ratio and geological conditions: the

case of Garner valley downhole array in Southem California.

Bull. Seism. Soc. Am. 86,306-31 9

Tucker, B.€., J.L. King, D. Hatzfeld, and I.L. Nersesov. (1 984).

Observations of hard-rock site effects. Bull. Seism. Soc. Am. 74,

121 -136