Microtremor Array Measurements for Site Effect Investigations
J. Louie 2/24/2005 Refraction Microtremor for Shallow Shear Velocity in California Urban Basins John...
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Transcript of J. Louie 2/24/2005 Refraction Microtremor for Shallow Shear Velocity in California Urban Basins John...
J. Louie 2/24/2005J. Louie 2/24/2005
Refraction MicrotremorRefraction Microtremorfor Shallow Shear Velocityfor Shallow Shear Velocityin California Urban Basinsin California Urban Basins
Refraction MicrotremorRefraction Microtremorfor Shallow Shear Velocityfor Shallow Shear Velocityin California Urban Basinsin California Urban Basins
John Louie, Nevada Seismological LabUNR students: J. B. Scott, T. Rasmussen, W. Thelen, M. Clark
Collaborators:S. Pullammanappallil & B. Honjas, Optim LLCW. J. Stephenson, R. A. Williams, & J. K. Odum, USGS
Support from:IRIS-PASSCAL Instrument Center at NMT
More details at www.seismo.unr.edu/hazsurv
John Louie, Nevada Seismological LabUNR students: J. B. Scott, T. Rasmussen, W. Thelen, M. Clark
Collaborators:S. Pullammanappallil & B. Honjas, Optim LLCW. J. Stephenson, R. A. Williams, & J. K. Odum, USGS
Support from:IRIS-PASSCAL Instrument Center at NMT
More details at www.seismo.unr.edu/hazsurv
J. Louie 2/24/2005J. Louie 2/24/2005
ReMi measures Rayleigh dispersion with linear refraction arrays (paper by Louie, April 2001 BSSA).
Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
100-m depth resolution
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
What if energy arrives transverse to the linear array?Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
Majority of energy piles up close to the minimum-velocity envelope.
Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
Fieldwork is quick and simple; best results in cities.Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
Low-frequencies, 1-20 Hz, so bad geophone plants still work.
Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
Fieldwork is quick and simple; best results in cities.Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
Fieldwork is quick and simple; best results in cities.Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
Initial funding from SCEC, UNR, VUW, Optim LLC
J. Louie 2/24/2005J. Louie 2/24/2005
ReMi has classified hard and soft sites around the world by measuring V30, average shear velocity to 30 m depth.
Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity
J. Louie 2/24/2005J. Louie 2/24/2005
Four deep suspension logs in Santa Clara Valley
Collaboration with Stephenson, Williams, Odum (USGS), and Pullammanappallil (Optim)
Refraction, MASW, and ReMi at each hole
ReMi-Borehole ReMi-Borehole ComparisonComparison
ReMi-Borehole ReMi-Borehole ComparisonComparison
J. Louie 2/24/2005J. Louie 2/24/2005
No surface method can match log details.ReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole Comparison
J. Louie 2/24/2005J. Louie 2/24/2005
Depth-averaged velocities are a good match.But CCOC’s LVZ is a problem.
ReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole Comparison
J. Louie 2/24/2005J. Louie 2/24/2005
Joyner et al. (1981) quarter-wavelength spectra similar at important frequencies.ReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole Comparison
J. Louie 2/24/2005J. Louie 2/24/2005
We Follow Field’s (2001) Amplification-Mapping StrategyWe Follow Field’s (2001) Amplification-Mapping StrategyWe Follow Field’s (2001) Amplification-Mapping StrategyWe Follow Field’s (2001) Amplification-Mapping Strategy
Two Inputs for Microzonation: V30 and Basin Depth (Z1.5?)
J. Louie 2/24/2005J. Louie 2/24/2005
July 2003 San Gabriel Valley & Los AngelesShallow Shear-Velocity TransectsShallow Shear-Velocity TransectsShallow Shear-Velocity TransectsShallow Shear-Velocity Transects
B-C
C-D
D
D-E
Transect mapped on NEHRP hazard class map by Wills, from SCEC Phase 3 Report
Supported by USGS, NEHRP ERP and IRIS-PASSCAL
J. Louie 2/24/2005J. Louie 2/24/2005
Los Angeles TransectLos Angeles TransectLos Angeles TransectLos Angeles Transect
Approximately 60 km in lengthApproximately 60 km in length Followed San Gabriel River Bike PathFollowed San Gabriel River Bike Path 20 m takeout interval, 300 m array, recorded for 30 min20 m takeout interval, 300 m array, recorded for 30 min
4 teams, 3 people each, 4.5 days4 teams, 3 people each, 4.5 days 120 IRIS/PASSCAL “Texan” single-channel recorders 120 IRIS/PASSCAL “Texan” single-channel recorders
mated to a vertical 4.5-Hz geophonemated to a vertical 4.5-Hz geophoneSupported by USGS, NEHRP ERP and IRIS-PASSCAL
J. Louie 2/24/2005J. Louie 2/24/2005
Los Angeles Transect:Los Angeles Transect:Levee EffectsLevee Effects
Los Angeles Transect:Los Angeles Transect:Levee EffectsLevee Effects
VV30 30 levee: 245 m/s levee: 245 m/s
VV30 30 non-levee: 241 non-levee: 241 m/sm/s
J. Louie 2/24/2005J. Louie 2/24/2005
Los Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 Results
J. Louie 2/24/2005J. Louie 2/24/2005
Boreholes in Open-File ReportsBoreholes in Open-File ReportsBoreholes in Open-File ReportsBoreholes in Open-File Reports
Four within 1 Four within 1 km of transectkm of transect
Also an Also an incomplete incomplete posting at posting at ROSRINE, ROSRINE, Pico Rivera 2Pico Rivera 2
Borehole Database Comparison—Data points within 1 km of transect
Source, Transect Array Number
Distance from Borehole
30-m Shear Velocity
% Difference NEHRP Class
Gibbs et al. (2000) ----------------- 226.9 m/s ---------------- D
This study, 186 850 m 309 m/s 36.18% D
This study, 187 269 m 301 m/s 32.66% D
This study, 188 345 m 284 m/s 25.17% D
This study, 189 930 m 251 m/s 10.62% D
Gibbs et al. (2001) ----------------- 298.7 m/s ---------------- D
This study, 140 661 m 401 m/s 34.25% C
This study, 141 442 m 338 m/s 13.15% D
This study, 142 955 m 424 m/s 41.95% C
Gibbs et al. (2001) ----------------- 544.7 m/s ---------------- C
This study, 121 870 m 580 m/s 6.48% C
This study, 122 673 m 538 m/s -1.23% C
This study, 123 997 m 498 m/s -8.57% C
Wills and Silva (1998)
----------------- 339.06 m/s ---------------- D
This study, 158 939 m 317 m/s -6.51% D
This study, 159 973 m 306 m/s -9.75% D
ROSRINE Borehole ----------------- 241.54 m/s ---------------- D
This study, 153 492 m 425 m/s 75.95% C
This study, 154 221 m 381 m/s 57.74% C
This study, 155 775 m 337 m/s 39.52% D
J. Louie 2/24/2005J. Louie 2/24/2005
Rosrine/USGS Pico Rivera 2Rosrine/USGS Pico Rivera 2Rosrine/USGS Pico Rivera 2Rosrine/USGS Pico Rivera 2 Good correlation with transect below 8 m depth.Good correlation with transect below 8 m depth.
0
50
100
150
200
250
0 200 400 600 800 1000 1200Shear-wave Velocity, m/s
Depth, m
ROSRINE picoriv2 borehole
SGRiv Survey Station 155A: ReMi
SGRiv Survey Station 156A: ReMi
SGRiv Survey Station 157A: ReMi
J. Louie 2/24/2005J. Louie 2/24/2005
Los Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 Results
J. Louie 2/24/2005J. Louie 2/24/2005
Los Angeles Transect: Full ResultsLos Angeles Transect: Full ResultsLos Angeles Transect: Full ResultsLos Angeles Transect: Full Results
J. Louie 2/24/2005J. Louie 2/24/2005
Measured VMeasured V3030 vs Wills et al. (2000) vs Wills et al. (2000)Measured VMeasured V3030 vs Wills et al. (2000) vs Wills et al. (2000)
Average Average measurements within measurements within ranges for classes B-ranges for classes B-C, D, and D-EC, D, and D-E
N. San Gabriel Val. N. San Gabriel Val. Measurements Measurements average above average above predicted C-D rangepredicted C-D range
60 new C-D data 60 new C-D data pointspoints
583 580
330
255
100
200
300
400
500
600
700
800
Wills et al. (2000) Predicted Hazard Class
Measured 30-m Shear Velocity
2003 UNR Measurements
Measured Averages
Wills et al. (2000) Averages andRanges
B
B-C
CC-D
D D-EE
J. Louie 2/24/2005J. Louie 2/24/2005
VV3030 vs Geologic Unit vs Geologic UnitVV3030 vs Geologic Unit vs Geologic Unit
Large VLarge V3030 variation inside each unit variation inside each unit
Large VLarge V30 30 variation between units variation between units
J. Louie 2/24/2005J. Louie 2/24/2005
VV3030 vs Soil Type vs Soil TypeVV3030 vs Soil Type vs Soil Type
In general, large VIn general, large V3030 variation within units variation within units Units 2 and 5 may be NEHRP DUnits 2 and 5 may be NEHRP D
Large VLarge V3030 variation between units variation between units
J. Louie 2/24/2005J. Louie 2/24/2005
VV3030 vs Riverbank Elevation vs Riverbank ElevationVV3030 vs Riverbank Elevation vs Riverbank Elevation Fast, bouldery alluvium at higher elevations on River’s alluvial fanFast, bouldery alluvium at higher elevations on River’s alluvial fan
River Profile vs. 30-m Shear Velocity
0
50
100
150
200
250
300
0 10 20 30 40 50 60
Distance from San Gabriel Range Front (km)
Elevation (m)
200
300
400
500
600
700
800
30-m Shear Velocity (m/s)
Levee & Path Elevation Profile
30-m Shear Velocity
J. Louie 2/24/2005J. Louie 2/24/2005
Spatial Statistics on VSpatial Statistics on V3030Spatial Statistics on VSpatial Statistics on V3030
Line in log-log Line in log-log spectrum means spectrum means fractalfractal
V30 less V30 less predictable as predictable as distance from distance from measurement measurement increasesincreases
““Noise Floor”- Noise Floor”- minimum minimum variance reached variance reached at 700 m at 700 m separationseparation
Incorporate Incorporate fractal dimension fractal dimension into PSHA?into PSHA?
San Gabriel River Vs30 Transect Spatial Power Spectra
SGRiv: y = 20823x -1.5913
R2 = 0.6705 D=1.70(D=1.78 w/o noise floor)
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
0.01 0.1 1 10
Spatial Frequency, /km
Power, m^2/s^2/km
NoiseFloor
J. Louie 2/24/2005J. Louie 2/24/2005
SummarySummarySummarySummary
ReMi allows rapid seismic shaking-hazard ReMi allows rapid seismic shaking-hazard
classification, as required by IBC2000.classification, as required by IBC2000.
Long ReMi transects can geophysically Long ReMi transects can geophysically
characterize spatial variations in shaking characterize spatial variations in shaking
hazard.hazard.
Mapped soil and geologic units do not reliably Mapped soil and geologic units do not reliably
predict the measured Vpredict the measured V3030..
210 Measurements in LA match predictions, 210 Measurements in LA match predictions,
add to class C-D data, and quantify spatial add to class C-D data, and quantify spatial
variance.variance.
ReMi allows rapid seismic shaking-hazard ReMi allows rapid seismic shaking-hazard
classification, as required by IBC2000.classification, as required by IBC2000.
Long ReMi transects can geophysically Long ReMi transects can geophysically
characterize spatial variations in shaking characterize spatial variations in shaking
hazard.hazard.
Mapped soil and geologic units do not reliably Mapped soil and geologic units do not reliably
predict the measured Vpredict the measured V3030..
210 Measurements in LA match predictions, 210 Measurements in LA match predictions,
add to class C-D data, and quantify spatial add to class C-D data, and quantify spatial
variance.variance.
J. Louie 2/24/2005J. Louie 2/24/2005
Most of Strip, Downtown; south side of Basin only
79 sites total
1145 well logs & geologic mapping
Las Vegas Las Vegas TransectTransect
J. Louie 2/24/2005J. Louie 2/24/2005
Some correlation to faulting, soil type?Las Vegas TransectLas Vegas Transect
J. Louie 2/24/2005J. Louie 2/24/2005
Geologic Info to Predict VGeologic Info to Predict Vss
NSL, July ‘03, sponsored by LLNL
Can soil maps predict VCan soil maps predict Vss??
J. Louie 2/24/2005J. Louie 2/24/2005
How to Extrapolate Shallow VHow to Extrapolate Shallow Vss
Correlate Correlate transect transect measurements measurements against Soil against Soil Map.Map.
Correlate 75 Vs Correlate 75 Vs values against values against stratigraphic stratigraphic model.model.
Soil
Stratigraphy
J. Louie 2/24/2005J. Louie 2/24/2005
How to Extrapolate Shallow VHow to Extrapolate Shallow Vss Predictions are good where there are many measurements.Predictions are good where there are many measurements.
Comparison of Las Vegas Vs30 Data and
200
300
400
500
600
700
0 2 4 6 8 10 12 14
Transect Distance South of Cheyenne, km
Vs30, km/s
UNR Transect Vs30 Measurements
Soil-Map Predictions
Stratigraphic-Model Predictions
J. Louie 2/24/2005J. Louie 2/24/2005
How to Extrapolate Shallow VHow to Extrapolate Shallow Vss
Predictions are not Predictions are not good where there good where there only sparse only sparse measurements.measurements.
Soil map Soil map predictions are not predictions are not conservative.conservative.
Stratigraphic model Stratigraphic model predictions are, at predictions are, at least, conservative.least, conservative.
Off-Transect Measurements and Predictions
200
400
600
800
1000
200 400 600 800 1000
Measured Vs30, m/s
Predicted Vs30, m/s
Soil-Map PredictionsStratigraphic-Model PredictionsNot ConservativeConservative