CEE 437 Lecture 4

Stereonets

January 15, 2009

Thomas Doe

Bill Dershowitz

Overview

Types of Orientation Data Lines

Planes

Representing them on a Stereonet Polar Plot

Equatorial Plot

Applications Slope stability

Earthquake Analysis

Problem set - out 1/20, due 1/29

Orientations of Objects

Lines: Trend – orientation of horizontal component measured

from north

Plunge – inclination downward from horizontal

Planes Strike and Dip

Quadrant notation

360 Notation

Pole – line normal to plane measured DOWN (Lower Hemisphere)

Dip Vector – Direction of Maximum Dip or Downward Inclination in a Plane

010

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170180

190

200

210

220

230

240

250

260

270

280

290

300

310

320

330

340

350

Schmidt Equal-Area Projection, Lower Hemisphere

Sutu Den Seismic Zones

< 0%

0 -- 1.8%

1.8 -- 3.6%

3.6 -- 5.4%

5.4 -- 7.3%

7.3 -- 9.1%

9.1 -- 10.9%

10.9 -- 12.7%

12.7 -- 14.5%

14.5 -- 16.3%

16.3 -- 18.2%

> 18.2%

# Points: 106

2X 1X2XS

T

8I9I

12I

6X

3X 5X

4X

0 1020

30

40

50

60

70

80

90

100

110

120

130

140

150160

170180190200

210

220

230

240

250

260

270

280

290

300

310

320

330340

350

Schmidt Equal-Area Projection, Lower Hemisphere

All Data Corrected

PoleDip

Vector

Strike

Which is Best?

Quadrant notation cumbersome and hard to use in calculation

Pole, 360 notation, and dip vector compact

Dip vector useful for engineering (problem is biasing of density

in graphics towards vertical – all vertical planes have

same dip vector regardless of strike)

Strike

Dip

Orientation Relationships

Strike and Dip Quadrant – NE or NW, 0-90 degrees, dip direction for NE

Strikes: NW or SE; for NW strikes NE or SW

360 – Strike measured 0-360; Strike is 90 counterclockwise of dip direction (or dip is 90 clockwise of strike)

Dip Vector Direction of maximum dip

Trend – 360 strike + 90

Plunge – dip angle

Pole Normal to plane (lower hemisphere)

Trend – 180 from dip; 90 counterclockwise of strike

Plunge – 90 - dip

Class Exercises

Define line directions on polar plot

Defining a plane

Pole, Dip Vector, great circle

Define plane based on two lines (plane is the

locus of all coplanar lines)

Defining a friction angle as small circle (polar

plot)

Kinematic failure analysis of block and wedges

Hoek, E. and J.

Bray, 1981, Rock

Slope

Engineering

Hoek, E. and J.

Bray, 1981, Rock

Slope

Engineering

Hoek, E. and J.

Bray, 1981, Rock

Slope

Engineering

Hoek, E. and J.

Bray, 1981, Rock

Slope

Engineering

Focal Plane Solutions for

Earthquakes

Stereonet “Beach Ball” Plots

Determine Type of Movement and Fault

Earthquake on a vertical

plane

Edited from Cox and Hart. Plate Tectonics – How it works.

nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

Earthquake Planes

USGS

nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

Data on the

surface,

interpreted

in 3D

Cox and Hart. Plate Tectonics – How it works.nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

With a lot of recordings we can reconstruct

faults with any orientations

Cox and Hart. Plate Tectonics – How it works.

nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

Fault types and “Beach Ball”

plots

USGS

nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

Example Focal

mechanism diagrams

on mid-ocean ridges

Stein and Wysession, An Introduction to seismology, earthquakes and Earth structurenctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

Same N-S fault, different

slip direction

Stein and Wysession, An Introduction to seismology, earthquakes and Earth structurenctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt