Fine-Scale Delineation of the Location of and 

Relative Ground Shaking within the San Andreas 

Fault Zone at San Andreas Lake, San Mateo 

County, California

Open-File Report 2013–1041

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013 

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Suggested citation:

Catchings, R.D., Rymer, M.J., Goldman, M.R., Prentice, C.S., and Sickler, R.R., 2013, Finescale delineation of the location of and relative ground shaking within the San Andreas Fault 

zone at San Andreas Lake, San Mateo County, California: U.S. Geological Survey Open-File 

Report 2013–1041, 53 p.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

Executive Summary ..........................................................................................................................1

Introduction .......................................................................................................................................2

Methodology .....................................................................................................................................3

Data Acquisition ................................................................................................................................4

Profile 6 (a, b, c)............................................................................................................................5

Profile 8 .........................................................................................................................................5

Profile 9 .........................................................................................................................................6

Data Processing................................................................................................................................6

Velocity Analysis and Images............................................................................................................6

Profile 6 (a, b, c): P-wave Velocities..............................................................................................7

Profile 6 (a, b, c): S-wave Velocities..............................................................................................8

Profile 6 (a, b, c): Vp/Vs Ratios .....................................................................................................8

Profile 6 (a, b, c): Poisson’s Ratios................................................................................................9

Profile 8: P-wave Velocities ...........................................................................................................9

Profile 8: S-wave Velocities .........................................................................................................10

Profile 8: Vp/Vs Ratios.................................................................................................................10

Profile 8: Poisson’s Ratios...........................................................................................................10

Profile 9: P-wave Velocities .........................................................................................................11

Guided Waves................................................................................................................................. 11

Recording Profile Line 6c: Guided Waves, P-Wave Sensors ......................................................11

Recording Profile 8: Guided Waves, P-Wave Sensors................................................................11

Recording Profile 8: Guided Waves, S-Wave Sensors................................................................12

Recording Profile 9: Guided Waves, P-Wave Sensors................................................................12

Discussion and Summary of Structures Along the Profiles .............................................................13

Acknowledgments...........................................................................................................................14

References Cited ............................................................................................................................14

Appendix 1.Acquisition and Geometry for Profile 6a .......................................................................46

Appendix 2.Acquisition and Geometry for Profile 6b .......................................................................47

Appendix 3.Acquisition and Geometry for Profile 6c .......................................................................49

Appendix 4.Acquisition and Geometry for Profile 8 .........................................................................51

Appendix 5.Acquisition and Geometry for Profile 9 .........................................................................52

Figures

1. (a) Google Earth photograph showing the locations of seismic profiles 6a, 6b, 6c, 8, 

and 9 that were acquired along the eastern shore of San Andreas Lake in 2008, 

2009 and 2011.............................................................................................................................17

2. Google Earth photograph showing seismic profiles 6a, 6b, and 6c.............................................19

3. (a) Google Earth photograph showing seismic profile 8..............................................................20

4. Google Earth photograph showing seismic profile 9 ...................................................................22

5. (a) Refraction tomography P-wave velocity models for profiles 6 (6a, b, c).................................23

6. (a) Refraction tomography S-wave velocity models for profiles 6 (6a, b, c) from data acquired 

in 2008 (profile 6a), 2009 (profile 6b) and 2011 (profile 6c). ........................................................25
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7. Photo near profile 6c ...................................................................................................................27

8. (a) Vp/Vs models for profile 6 (a,b,c), developed from the refraction tomography 

P- and S-wave models of figures 5 and 6. ...................................................................................28

9. (a) Poisson’s ratio (PR) models for profile 6, developed from the refraction tomography P- and 

S-wave models of figures 5 and 6................................................................................................29

10. Refraction tomography P-wave velocity model for profile 8 with the locations of surface 

ruptures (at red arrows) mapped by Schussler (1906).................................................................30

11. Refraction tomography S-wave velocity model for profile 8 with the locations of surface 

ruptures (at red arrows) mapped by Schussler (1906).................................................................31

12. Vp/Vs model for profile 8 developed from the refraction tomography P- and S-waves models 

of figures 10 and 11 .....................................................................................................................32

13. Poisson’s Ratio (PR) model for profile 8 developed from the refraction tomography P- and Swaves models of figures 10 and 11..............................................................................................33

14. Refraction tomography P-wave velocity model for profile 9.......................................................34

15. A comparison of peak-amplitude (horizontal-component) guided waves recorded along profile 

8 with the S-wave velocity model for profile 6 ..............................................................................35

16. A comparison of peak-amplitude (vertical-component) guided waves recorded along profile 8 

with the P-wave velocity model for profile 6. ................................................................................39

17. A comparison of peak-amplitude (vertical-component) guided waves recorded along profile 9 

with the P-wave velocity model for profile 9. ................................................................................42

18. Map from Schussler (1906) showing off-fault displacements associated with the 1906 San 

Francisco earthquake at three separate locations (profiles L, N, and N’) just south of San 

Andreas Lake (SAL).....................................................................................................................45
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Conversion Factors and Datums

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

Velocity

centimeter per second (cm/s) 0.03281 foot per second (ft/s)

meter per second (m/s) 3.281 foot per second (ft/s) 

Datum

Vertical coordinate information is referenced to the World Geodetic System of 1984 (WGS84) datum.
Fine-Scale Delineation of the Location of and 

Relative Ground Shaking within the San Andreas 

Fault Zone at San Andreas Lake, San Mateo 

County, California

R.D. Catchings, M.J. Rymer, M.R. Goldman, C.S. Prentice, and R.R. Sickler

Executive Summary 

The San Francisco Public Utilities Commission is seismically retrofitting the 

water delivery system at San Andreas Lake, San Mateo County, California, where the

reservoir intake system crosses the San Andreas Fault (SAF). The near-surface fault 

location and geometry are important considerations in the retrofit effort. Because the SAF 

trends through highly distorted Franciscan mélange and beneath much of the reservoir, 

the exact trace of the 1906 surface rupture is difficult to determine from surface mapping 

at San Andreas Lake. Based on surface mapping, it also is unclear if there are additional 

fault splays that extend northeast or southwest of the main surface rupture. To better 

understand the fault structure at San Andreas Lake, the U.S. Geological Survey acquired 

a series of seismic imaging profiles across the SAF at San Andreas Lake in 2008, 2009, 

and 2011, when the lake level was near historical lows and the surface traces of the SAF 

were exposed for the first time in decades. We used multiple seismic methods to locate 

the main 1906 rupture zone and fault splays within about 100 meters northeast of the 

main rupture zone. Our seismic observations are internally consistent, and our seismic 

indicators of faulting generally correlate with fault locations inferred from surface 

mapping. We also tested the accuracy of our seismic methods by comparing our 

seismically located faults with surface ruptures mapped by Schussler (1906) immediately 

after the April 18, 1906 San Francisco earthquake of approximate magnitude 7.9; our 

seismically determined fault locations were highly accurate. Near the reservoir intake 

facility at San Andreas Lake, our seismic data indicate the main 1906 surface rupture 

zone consists of at least three near-surface fault traces. Movement on multiple fault traces 

can have appreciable engineering significance because, unlike movement on a single 

strike-slip fault trace, differential movement on multiple fault traces may exert

compressive and extensional stresses on built structures within the fault zone. Such 

differential movement and resulting distortion of built structures appear to have occurred 

between fault traces at the gatewell near the southern end of San Andreas Lake during the 

1906 San Francisco earthquake (Schussler, 1906). In addition to the three fault traces 

within the main 1906 surface rupture zone, our data indicate at least one additional fault 

trace (or zone) about 80 meters northeast of the main 1906 surface rupture zone. Because 

ground shaking also can damage structures, we used fault-zone guided waves to 
2

investigate ground shaking within the fault zones relative to ground shaking outside the 

fault zones. Peak ground velocity (PGV) measurements from our guided-wave study 

indicate that ground shaking is greater at each of the surface fault traces, varying with the 

frequency of the seismic data and the wave type (P versus S). S-wave PGV increases by 

as much as 5–6 times at the fault traces relative to areas outside the fault zone, and Pwave PGV increases by as much as 3–10 times. Assuming shaking increases linearly with

increasing earthquake magnitude, these data suggest strong shaking may pose a 

significant hazard to built structures that extend across the fault traces. Similarly complex 

fault structures likely underlie other strike-slip faults (such as the Hayward, Calaveras, 

and Silver Creek Faults) that intersect structures of the water delivery system, and these 

fault structures similarly should be investigated. 

Introduction

The active strand of the San Andreas Fault (SAF) trends beneath and along the 

eastern shore of San Andreas Lake on the San Francisco Peninsula near San Francisco, 

California (figs. 1a and 1b). Intake pipes used by the San Francisco Public Utilities 

Commission (SFPUC) extend from San Andreas Lake across the active strand of the 

SAF. To retrofit the water delivery system and make it more resistant to failure 

associated with ground rupture, knowledge of the location of the SAF and associated 

near-surface fault traces is needed. This report presents results from seismic imaging 

studies at San Andreas Lake that were undertaken in 2008, 2009, and 2011. 

In June 2011, the U.S. Geological Survey acquired a series of seismic imaging 

profiles across the 1906 surface rupture area of the SAF at San Andreas Reservoir in San 

Mateo County, California, approximately 20 km southwest of downtown San Francisco. 

Each year when the seismic data were acquired, water levels were lowered to near 

historical levels, progressively exposing the surface traces of the 1906 SAF rupture zone 

at San Andreas Lake for the first time in decades. The relatively low water levels 

permitted detailed land-based imaging of the fault zone using advanced seismic 

techniques. The objectives of the seismic surveys were to: 

1. Delineate in fine-scale (about 1 m), near-surface principal and auxiliary traces of 

the SAF at San Andreas Lake (where possible) using seismic imaging methods, 

including (a) tomographic P-wave velocity imaging, (b) tomographic S-wave 

velocity imaging, (c) P-wave velocity divided by S-wave velocity (Vp/Vs) ratio 

imaging, (d) Poisson’s ratio imaging, (e) seismic reflection imaging (where

possible), and (f) fault-zone guided wave imaging. 

2. Measure ground shaking and peak amplitudes of seismic waves within the nearsurface fault zone using fault zone guided waves and to compare the relative 

ground shaking within and outside of individual fault zones. 

3. Correlate geologically mapped faults with seismic indicators (high Vp/Vs and 

Poisson’s ratios, diffractions, offset reflections, low S-wave velocities, changes in 

topography, and localized high amplitudes from guided waves) to evaluate the 

accuracy of previously mapped faults. 

4. Determine the subsurface geometry of faults near the main surface rupture 

resulting from the 1906 earthquake. 

We originally planned to accomplish these objectives by acquiring two faultcrossing seismic profiles near the proposed intake facility (see fig. 1). However, because 
3

of the unusual opportunity to directly image the SAF and to better understand its threedimensional complexities, we instead acquired three separate seismic profiles in 2011 and 

combined our 2011 findings with two additional profiles (profiles 6a and 6b, acquired in 

2008 and 2009, respectively). 

Methodology

In many locations, standard seismic reflection imaging is ideal for locating

individual fault traces; however, at San Andreas Lake, rocks within and adjacent to the 

fault zone consist of highly deformed Franciscan mélange. Seismic reflection methods 

typically cannot image such complex structures, as they have little horizontal layering

required for the reflection method to yield useful results. In this study, we used highresolution refraction tomography and measurements of guided waves to characterize the 

fault traces along three separate profiles, which we refer to as profile 6, profile 8, and 

profile 9 (figs. 1a and 1b). Our refraction tomography method uses both P- and S-waves 

along profiles 6 and 8, but because of a water body in the middle of profile 9, only Pwaves were used along that profile. The refraction tomography method measures the 

velocities at which seismic waves travel through the subsurface, and because general 

classes of subsurface materials propagate seismic waves at known velocities, the 

subsurface materials and their physical conditions can be inferred from the velocity 

measurements. 

We also use P and S waves to identify zones of faulting based on several criteria.

First, within hard rocks, fault zones are known to transmit P-waves at significantly lower 

velocities than adjacent rocks that are not faulted (Aki and Lee, 1976; Mooney and 

Luetgert, 1982; Mooney and Ginzburg, 1986; Jarchow and others, 1994; Catchings, 

1999; Catchings and others, 2002). By imaging areas of relatively low velocities in hard 

rock, the fault location can be inferred, especially the main trace. Such low-velocity 

zones (LVZs) also can occur as abrupt lateral changes in velocity, with relatively higher 

velocities on either side of the fault (Catchings and others, 2002, 2008, 2009, 2010). 

Second, fault zones typically form barriers to the lateral flow of groundwater. As a result, 

groundwater is typically deeper on the downslope side of the fault. From numerous 

studies, we have identified the top of groundwater by modeling the 1,500-m/s velocity 

contour (Catchings and others, 1999a, 1999b, 2000, 2006a, 2006b, 2007, 2008, 2009), 

which is the velocity at which P-waves travel through water (Schon, 1996). Therefore, 

our empirical studies have shown that an abrupt vertical step in the 1,500 m/s velocity 

contour typically coincides with a near-surface fault. Third, near-surface, water-saturated 

sediments within fault zones can mask the low P-wave velocities of fault zones, such that 

no near-surface low P-wave velocity zone is observed, making the fault zone less obvious 

in the near-surface sediments (Catchings and others, written communication, 2013). 

However, S waves, which are much less sensitive to groundwater saturation, can be used 

to image the low-velocity zones near the surface, whereby the fault zone will be lower in 

velocity than the adjacent rocks. Fourth, mechanical faulting of rocks causes a greater 

reduction in S-wave velocities than P-wave velocities, such that the ratio of P-to S-wave 

velocities can be particularly diagnostic of fault zones. Poisson’s ratio, which also can be 

calculated from the P- and S-waves (Thomsen, 1990), also will be locally high over the 

fault zones. Fifth, topography usually changes across a fault zone (Catchings and others, 

2010). High-precision global positioning system (GPS) measurements of the geophones 
4

and shot point locations can be used to construct topographic profiles across the fault 

zones to better observe subtle changes in topography. Sixth, guided waves are known to 

travel along fault zones as high-amplitude energy when the seismic source originates 

within the fault zone (Cormier and Spudich, 1984; Li and others, 1994; Li and Vidale, 

1996; Li and others, 1997; Spudich and Olsen, 2001; Fohrmann and others, 2004). 

Seismic sources, placed within fault zones at appreciable epicentral distances from 

densely spaced seismic recording arrays that are deployed across fault zones can be used 

to measure relative amplitudes of energy traveling along fault zones. The locations of 

seismic sensors that display high-amplitude energy can be used to infer fault traces in the 

near surface. Where all or several of these seismic indicators of faulting coincide, 

individual fault traces can be strongly inferred. 

Data Acquisition

To acquire high-resolution P-wave refraction data along each profile, we used an 

array of Mark ProductsTM, single-element, 40-hertz (Hz), vertical-component geophones 

spaced at either 1-m increments (profiles 6 and 8) or 5-m increments (profile 9). The 

geophones were connected to refraction cables, which were connected to one or more 60-

channel Geometrics RX 60TM seismographs. Both P- and S-wave seismic data were 

acquired along profiles 6 and 8. However, because part of profile 9 was underwater, we 

acquired only P-wave data along profile 9. We used Mark ProductsTM single-element, 

horizontal-component, 4.5-Hz geophones to record the S waves. P-wave seismic sources 

consisted of either 200- or 400-grain Betsy SeisgunTM shots in boreholes or 

sledgehammer strikes to steel plates placed on the ground. S-wave sources were 

generated by striking a steel or wooden block horizontally with a sledgehammer. For 

each of the seismic profiles, a P-wave seismic source was placed at the location of each 

vertical-component geophone, and an S-wave seismic source was placed at the location 

of every other horizontal-component geophone, with both types of sources offset laterally 

from each geophone by 1 m or less. For seisgun blasts, shot timing was determined 

electronically at the seismic source when a hammer, used to trigger the seisgun, electrically 

closed contact with the Betsy SeisgunTM, sending an electrical signal by radio to the 

seismograph. For hammer sources, we also used an electronic trigger, which initiated when 

the hammer closed contact with a metal strike plate on the ground surface. To enhance the 

recorded seismic energy generated by hammer sources, we used multiple hammer strikes and 

stacked (summed) the multiple strikes into a single shot gather. For S-wave sources, we 

recorded two hammer strikes on each side of the aluminum block and, in the laboratory, we 

reversed the polarity of two of the strikes. We then stacked all four hammer blows to 

generate one higher amplitude shot gather. Two seconds of data for each seismic source 

(seisgun blast and hammer strike) were recorded in SEG-2 format on the hard drive of the 

seismographs during field acquisition. The data were later transferred to 4-mm tape in SEGY format for long-term storage. Each shot and geophone location (latitude, longitude, and 

altitude) was surveyed using a high-precision GPS, with accuracies of a few centimeters

(See appendixes 1–5). 

We also acquired guided-wave data along seismic profiles 6c, 8, and 9 by 

recording seismic energy that was generated within the known fault zone (main 1906 

surface rupture zone) at profiles 6c and 8. The maximum source-receiver offset was 

approximately 1.6 km for profiles 6c and 8. For guided waves measured along profile 6c, 
5

we left the profile-6c refraction array in position with vertical-component geophones, and a

seismic source (0.45 kg blast) was input into the known surface rupture zone at profile 8. For 

guided waves measured along profile 8, the seismic sources were located at profile 6c, and 

the data were first recorded with vertical-component geophones. We then replaced the 

vertical-component geophones along profile 8 with horizontal-component geophones, and the 

seismic source (at profile 6c) was repeated. The data were recorded along both profiles for 

~16 seconds. The location of the main fault trace at profile 6c was determined from 

previous seismic measurements made prior to 2011, and the location of the main fault 

trace located at profile 8 was determined from the mapping of ground rupture by 

Schussler (1906) shortly after the 1906 earthquake. 

Profile 6 (a, b, c)

Profile 6 consisted of three separate seismic profiles that were acquired in three 

separate phases, an approximately 120-m-long profile in October 2008 (profile 6a), an 

approximately 60-m-long profile in November 2009 (profile 6b), and an approximately 

120-m-long profile in June 2011 (profile 6c). All these seismic profiles geographically 

overlapped to some degree. In 2008, we acquired the easternmost segment of profile 6

(profile 6a), which extended from the SFPUC paved access road to the 2008 San Andreas 

Lake shoreline (fig. 2). In 2009, the San Andreas Lake level was near historical lows, 

which allowed us to extend profile 6b an additional ~50 m west of the 2008 seismic 

profile (profile 6a). In 2011, the lake level was lowered even more relative to its 2009 

level, which allowed us to extend profile 6c an additional 12 m west of the 2009 seismic 

profile (profile 6b). When profile 6a was acquired in 2008, the westernmost 2 m of 

profile 6a were within water at the lake shoreline, and the westernmost ~10–15 m of 

profile 6a were acquired in wet (muddy) conditions at the surface. When profile 6b was 

acquired, all of profile 6b was dry at the surface except for the westernmost ~5 m. Thus, 

the geographically overlapping area with profile 6a was dry at the surface. When profile 

6c was acquired, all of profile 6c was dry at the surface, except for the westernmost 7 m.

Thus, the geographically overlapping area with profiles 6a and 6b was dry at the surface.

For guided waves, data were recorded on the inline recording array of profile 6c, and seismic 

sources (blasts) originated in the fault zone of the main SAF surface rupture at profile 8. We 

recorded the blasts located at profile 8 with only P-wave geophones that were deployed along 

profile 6. Prior to acquiring the data, we surveyed geophone and shot locations using a 

measuring tape. After acquisition, more precise (within plus-or-minus several centimeters) 

geophone and shot locations were surveyed using a GPS receiver. The geometry data for 

profiles 6a, 6b, and 6c are presented in appendixes 1, 2, and 3, respectively. 

Profile 8

In November 2009, we acquired an approximately 60-m-long, high-resolution, 

combined reflection and refraction profile (profile 8) across the SAF at a westward 

salient that projects into the eastern shore of San Andreas Lake, approximately 800 m 

from its southern end (fig. 3a). Profile 8 was located in the area mapped by Schussler 

(1906) after the 1906 earthquake, where surface rupturing occurred along several 

secondary traces, as well as along a main surface rupture. Profile 8 crossed the main 

surface rupture, a secondary rupture west of the main surface rupture, and along the 

projection of a secondary rupture east of the main rupture (fig. 3b). The 
6

refraction/reflection data along profile 8 were acquired in the same manner as described for 

profile 6. The geometry data for profile 8 are presented in appendix 4. For guided waves, data 

were recorded on the inline recording array of profile 8, and seismic sources (blasts) 

originated in the rupture zone of the 1906 main SAF surface rupture at profile 6c. We 

recorded the blasts at profile 6c with both P-wave and S-wave geophones that were deployed 

along profile 8. Prior to acquiring the data, we surveyed geophone and shot locations using a 

measuring tape. After acquisition, more precise (several centimeters) geophone and shot 

locations were surveyed using a GPS receiver. The geometry data for profile 8 are presented 

in appendix 4.

Profile 9

In June 2011, we acquired an approximately 120-m-long, high-resolution, 

combined reflection and refraction profile (profile 9), located approximately 1.3 km 

southeast of profile 6 and about 350 m northwest of profile 8. Profile 9 extended from a 

topographic high (then a small island) within San Andreas Lake to the easternmost shore 

of San Andreas Lake (fig. 4). Acquisition parameters for profile 9 are included in appendix 

5. P-wave seismic sources were generated by Betsy-SeisgunTM blasts (400 grain). The data 

were acquired in the same manner as described for profile 6, except the shot and sensor 

spacing was 5 m instead of 1 m so that a longer profile could be imaged. Additionally, for the 

submerged section of profile 9, geophones were placed on wooden closet rods that were 

inserted into the muddy bottom to prevent electrical shorts in the cable and geophone 

attachment. Along the area of profile 8 that was covered by water at the surface, seismic 

sources were placed directly within the water column, instead of in shallow boreholes. For 

guided waves, data were recorded on the inline recording array of profile 9, and seismic 

sources (blasts) originated in the rupture zone of the 1906 main SAF surface rupture at 

profile 8. We recorded the blasts at profile 8 with vertical-component geophones that were 

deployed along profile 9. Prior to acquiring the data, we surveyed geophone and shot 

locations using a measuring tape. After acquisition, more precise (several centimeters) 

geophone and shot locations were surveyed using a GPS receiver. The geometry data for 

profile 9 are presented in appendix 5. S waves were not recorded along profile 9 because of 

the water body located in the middle of the seismic profile. 

Data Processing

Shots along each seismic profile were assembled into shot gathers by merging 

data from each seismograph, where needed. We developed refraction tomography 

velocity images by measuring the first-arrival seismic energy on each seismogram from 

each shot along each of the seismic profiles and inverting those arrivals for velocity 

structure using the refraction tomography code of Hole (1992). Because of the relatively 

long recording array (240 channels or 1,200 m), both reflection and refraction data were 

simultaneously acquired. We processed the seismic data as shallow-depth refraction 

tomography velocity images and reflection images. However, as expected, the reflection 

images did not provide usable results because of the complex geology. 

Velocity Analysis and Images 

To develop tomographic P-wave seismic velocity models of the subsurface along 

the SFPUC seismic profiles, we inverted first-arrival travel times using seismograms 
7

from shot gathers along each seismic profile. In parameterizing the models for profiles 6 

and 8, we used 1-m by 1-m horizontal and vertical grid spacings, and for profile 9, we 

used 5-m by 5-m horizontal and vertical grid spacings. All models used 2-D starting 

models derived from composite 1-D velocity models, calculated from shot gathers. 

Multiple 2-D starting velocity models consistently yielded similar 2-D final velocity 

models, suggesting that the velocity structures are well resolved. Although only two 

reversing raypaths are required to obtain accurate velocities, the model is best resolved 

where we have the highest density of ray coverage. The minimum depth of velocity 

imaging is related to the shot and geophone spacings, the model grid spacing, the 

frequency of the data, and the amount of smoothing used in modeling. The maximum 

distance that clear first-arrival refractions could be measured on the shot gathers limited 

the maximum depth of velocity imaging. P-wave refractions typically penetrate to depths 

equal to about 25 percent of the maximum distance first arrivals can be measured, 

resulting in maximum imaging depths of about 10–40 m along most of our profiles. 

Profile 6 (a, b, c): P-wave Velocities

Because profiles 6a, 6b, and 6c were acquired along the same approximate trend, 

we show the profiles as a composite (figs. 5a, 5b, 6a, 6b, 8a, 8b, 9a, and 9b). The

presence of water in the subsurface significantly increases seismic P-wave velocities. As 

a result, areas that were wet during the acquisition phase (2008) of profile 6a have higher 

P-wave velocities than the same areas that were dry in 2009 and 2011, when the lake 

level had been lowered. Such a change in velocity is observed at the overlapping 

southwestern end of profile 6a and the northeastern ends of profiles 6b and 6c. These 

differences in P-wave velocities necessarily affect the Vp/Vs and Poisson’s ratios (figs. 

8a, 8b, 9a, and 9b). However, at multiple locations along the profile-6 composite, abrupt 

lateral P-wave velocity variations occur that are consistent with faulting. Along profile 

6a, P-wave velocities in the upper 40 m range from about 500 to 4,200 m/s (fig. 5a). 

Because water-saturated sediments typically have a minimum P-wave velocity of 1,500 

m/s, empirical observations have shown that the 1,500-m/s velocity contour coincides 

with the top of groundwater in the subsurface. Empirical data also show that abrupt 

vertical variations in the depth to the top of groundwater (1,500-m/s contour; see white 

contour in fig. 5a) often coincide with the subsurface faulting. Along profile 6, the top of 

groundwater (1,500 m/s, not including perched or thin aquifers) is offset by about 5 m 

near meter 45 of the profile 6a (fig. 5a). The increase in depth of the 1,500 m/s velocity 

contour coincides with the edge of a local basin between meters 20 and 40 of the seismic 

profile and also is near an abrupt change in topographic slope. Additionally, at depths of 

about 10–20 m below the surface, there is a well-defined low-velocity zone with a slight 

dip to the east. From the surface to the base of the P-wave velocity model for profile 6a, 

there is a large collective change in the velocity model near meter 45 that is consistent 

with other seismically imaged known fault zones. Along profile 6b (fig. 5a), there are 

similar abrupt variations in P-wave velocities near meters 23, 42, and 60 of the seismic 

profile. At each of those locations, there is a near-surface thickening of low-velocity 

rocks, an abrupt vertical step in the 1,500 m/s velocity contour (groundwater), and abrupt 

lateral variations (or a pronounced low-velocity zone) in the higher velocity rocks at 

depth. The location of the main 1906 surface rupture of the SAF, as inferred by 

geomorphic evidence, is approximately located near meter 23 of seismic profile 6b.
8

There, near-surface higher P-wave velocities (including the 1,500 m/s velocity contour) 

abruptly deepen to the west, and there is an overall westward decrease in P-wave 

velocities to the base of the velocity model. Similar variations near meters 35–40 and 55–

60 suggest the presence of additional near-surface fault traces within about 20 m of the 

main trace.

Profile 6 (a, b, c): S-wave Velocities

Along profile 6a, S-wave velocities in the upper 15 m range from about 160 to

650 m/s (fig. 6a). The subsurface materials with the lowest S-wave velocities are at the 

easternmost end of the seismic profile (on top of the hill) and at the westernmost part of 

the profile, where low-velocity (less than 250 m/s) deposits are about 7 m thick. The 

rocks with the highest velocities occur within a few meters of the surface along the slope 

of the hill along profile 6a. These higher velocity rocks appear to be segmented at about 

meter 60 of profile 6a, with an apparent 5-m-wide low-velocity zone that likely results 

from faulting. At about meter 40, the high-velocity rocks abruptly deepen, which also is 

consistent with faulting at that location. Along profile 6b, the S-wave velocities range 

from about 160 to about 340 m/s (fig.6a). Near-surface S-wave velocity contours are 

highly variable, which is consistent with the highly variable rock types and distorted 

strata observed at the surface (fig. 7). Below about 5 m depth, relatively higher velocity 

rocks also form complex structures, with an eastward-dipping wedge of higher velocity 

rocks that projects toward the surface near about meter 15 of the seismic profile.

Velocities along profile 6c range from about 180 to about 480 m/s (fig. 6b). In the near 

surface, the velocity contours are highly variable, as observed along profile 6b, and the 

deeper, higher velocity rocks are offset to greater depths west of meter 30 on the western 

side of the seismic profile. The observed S-wave velocity structures along profile 6a 

suggest near-surface faults between meters 30 and 50 and possibly another fault near the

western end of profile 6a. Along profiles 6b and 6c, there are similar indicators of nearsurface faults near meter 0 of profile 6b (~meter 15 of profile 6c), meter 15 of profile 6b 

(~meter 35 of profile 6c), and meters 33–40 of profile 6b (~meters 53–60 of profile 6c). 

Profile 6 (a, b, c): Vp/Vs Ratios

We developed tomographic models of Vp/Vs ratios along profile 6 by dividing Pwave velocities at each of the model nodes by the corresponding S-wave velocities (fig. 

8). Along profile 6a, S-wave propagation was not as efficient as P-wave propagation, 

owing to the weaker source and the surface vegetation on the side of the hill. As a result, 

S-wave refractions did not propagate along the entire profile, resulting in a shallower depth 

of velocity imaging relative to P-wave imaging. Because the Vp/Vs ratios are calculated on 

the basis of both P- and S-wave measurements, the Vp/Vs ratio model could be calculated 

only to the maximum depth of S-wave imaging (~10–15 m in depth). The highest Vp/Vs 

ratios range from about 7–8.6 at depths of 5–10 m, but relatively high Vp/Vs ratios (~2–5) 

occur in the near surface at multiple locations along the three seismic profiles. In near-surface 

consolidated materials, we have found that relatively high Vp/Vs ratios typically correlate

with near-surface fault traces. Along profile 6a, relatively high Vp/Vs ratios are observed 

near meters 50 and 10. High near-surface Vp/Vs ratios are observed near meters 0–10, 18–

25, 35–45, and 60 of profile 6b, correlating approximately with meters 18–22, 38–48, 55–65, 

respectively, of profile 6c (fig 8b). These areas of relatively high Vp/Vs ratios also correlate 
9

with areas of relatively low S-wave velocities and vertical steps in the 1,500 m/s P-wave 

velocity contour (top of groundwater), all of which are consistent with the presence of nearsurface fault traces. Vp/Vs ratios vary slightly between the profiles, which likely reflect

differences in the degree of groundwater saturation during the 3-year period over which the 

seismic data were acquired. 

Profile 6 (a, b, c): Poisson’s Ratios 

As done with Vp/Vs ratios, we developed tomographic models of Poisson’s ratios 

(PR) by calculating PR (fig. 9a) from Vp and Vs at each node of the seismic models 

using the following calculation from Thomsen (1990): 

ν = Ε/2μ -1 = (3Κ-2μ)/(6Κ+2μ) = ((Vp/Vs)2 -2)/2((Vp/Vs)2-2) (1)

where ν is Poisson’s Ratio (PR), 

μ is shear modulus, 

Ε is Young’s modulus, 

K is bulk modulus, 

Vp is P-wave velocity, and 

Vs is S-wave velocity.

Poisson’s ratio ranges from about 0 to 0.5 for most materials. Values near 0.5 are 

typical of water, but a few special rocks and minerals can have significantly higher or 

lower values of PR. For example, cristobalite (in volcanic rocks) can have a negative PR.

Most competent rocks have variable values of PR, ranging from about 0.25 to about 0.30. 

However, highly water-saturated sediments and rocks can have significantly higher 

values of PR, and quartz-rich rocks can have significantly lower values of PR. As related 

to this study, our empirical observations have shown that sediments and near-surface 

rocks with values of PR ~0.44 generally outline the top of groundwater, and higher 

values coincide with highly saturated sediments and rocks. PR along the seismic profiles 

varies in a manner similar to that of Vp/Vs ratios. Along profile 6a, PR ranges from about 

0.28 to about 0.49. Relatively high near-surface values of PR are observed near meters 

10–20, 50, and 115–120 in the near surface, and the highest values occur at depths about 

5–10 m beneath the center of the seismic profile and beneath the western end of profile 

6a. The zones of relatively high PR at depth and in the near surface also coincide with 

zones of faulting inferred from the other seismic images. Along profiles 6b and 6c, PR is 

high, ranging from about 0.46–0.49 (figs. 9a and 9b). When the seismic data were 

acquired, most of these rocks were highly saturated within about 0.3 m of the surface, so 

high values of PR are expected. The highest near-surface values of PR occur near meters 

~5–10, ~40–50, and ~60–65 along profile 6b, with similar geographic locations along 

profile 6c. 

Profile 8: P-wave Velocities

Along profile 8, P-wave velocities in the upper 15 m range from about 350 to

3,000 m/s (fig. 10). Low-velocity (less than 1,500 m/s) deposits vary along the profile, 

with a maximum thickness of about 8 m near the middle of the seismic profile. The 1,500 

m/s velocity contour generally coincides with the top of groundwater, and because of the 

importance of groundwater in delineating fault structures, the 1,500 m/s contour is 
10

highlighted here in white. At the time of data acquisition, the top of groundwater (1,500 

m/s) (not including perched or thin aquifers) was about 3 m deeper beneath the area of 

the main SAF trace, near the middle of the profile, and near the westernmost end of the 

seismic profile. The depth to the top of groundwater was not only determined on the basis 

of the 1,500 m/s velocity contour but also measured near the center of the seismic profile 

by auguring. However, because the area of the seismic profile is a salient that extends 

outward into San Andreas Lake and the topography is relatively flat, there is not a general 

downslope flow of groundwater. As a result, abrupt vertical offsets of the top of 

groundwater are absent, as seen along profile 6. The approximate known location of the 

main trace of the SAF coincides with a 5- to 10-m-wide P-wave low-velocity zone near 

the center of the profile at a depth of 5–10 m. 

Profile 8: S-wave Velocities

Along profile 8, S-wave velocities in the upper 15 m range from about 180 to 450 

m/s (fig. 11). Near the center of the seismic profile, S-wave velocities show a welldefined, low-velocity zone approximately centered over the 1906 main surface rupture of 

the SAF. The low-velocity zone is about 25 m wide based on matching highest velocities 

on either side, but it is about 5 m wide based on the lowest velocities near the surface. 

Unlike P-waves, which are influenced by the presence of water, S-wave low-velocity 

zones can indicate faulted strata and rocks from the surface to great depths. The abrupt 

termination of higher velocity rocks on either side of the low-velocity zone suggests 

individual faults at those locations. Relative to the remainder of the seismic profile, the 

westernmost end of the profile has the highest velocities, where Franciscan rocks are 

exposed at the surface. The overall relatively low S-wave velocities suggest that most of 

the subsurface materials are sediments or sedimentary rocks. 

Profile 8: Vp/Vs Ratios

Vp/Vs ratios for profile 8 were determined in much the same manner as described 

for profile 6. Vp/Vs ratios range from about 2 near the surface to more than 9 at depths of 

about 8–10 m below the surface (fig. 12). The two highest zones of Vp/Vs ratios are 

separated by a relatively low Vp/Vs zone, where P and S waves infer a low-velocity zone 

(fault). The nearest surface materials have Vp/Vs ratios of about 2 and are not suggestive 

of strata disrupted by faulting. However, at a depth of about 6 m, prominent zones of high 

Vp/Vs ratios are centered below the eastern areas of faulting observed in 1906. The 

westernmost zone of surface rupturing, however, does not include high Vp/Vs ratios at 

the scale of our image. 

Profile 8: Poisson’s Ratios 

Poisson’s ratios for profile 8 were determined in much the same manner as 

described for profile 6. PR values range from less than 0.1 in the very near surface to 0.48 

at depths of about 5–7 m (fig. 13). The general pattern of PR largely coincides with the 

1,500 m/s velocity contour, suggesting that PR is most sensitive to groundwater along 

profile 8. In the near surface, relatively high values of PR are associated with the 1906 

main trace and a mapped surface break near the western end of the seismic profile, but 

the projected fault east of the 1906 main trace does not show such high PR values. 
11

Profile 9: P-wave Velocities 

Along profile 9, P-wave velocities in the upper 30 m range from about 800 m/s to

3,600 m/s (fig. 14). Near-surface, low-velocity (less than 1,500 m/s) deposits are 

concentrated at the 2011 San Andreas Lake shoreline and on the high topographic 

(island) feature to the northwest. Based on P-wave velocities, we interpret unconsolidated 

sediments to be up to about 5–10 m thick. The top of groundwater (1,500 m/s) varies 

considerably along the profile, ranging from the near surface at the eastern end of the 

seismic profile, beneath the water body, and near the western end of the profile, to about 

5–10 m thick beneath the island topographic high and at the 2011 shoreline. Abrupt 

changes in the depth of the 1,500 m/s velocity contour occur a few meters east of the 

1906 mapped main fault trace, at the western end of the seismic profile, and a few meters 

east of the water body. At depth, relative low-velocity zones are located at about meter 

100 and about meter 20 of the seismic profile. The presence of the higher velocity rocks

suggests that near-surface faults are located near meters 20, 70, and 140. The P-wave 

seismic tomography velocity image largely coincides with the P-wave velocity image 

seen along profile 8, particularly near the main 1906 rupture. 

Guided Waves

We recorded seismic energy along profiles 6c, 8, and 9 from sources that were 

located within the known SAF zone at profiles 6 and 8. For data recorded along profiles 

6c and 8, the source was about 1.6 km from the recording arrays. For profile 9, the source 

was about 0.35 km from the recording array.

Recording Profile Line 6c: Guided Waves, P-Wave Sensors

We recorded guided waves along profile 6c using only vertical-component 

geophones, with sources located at profile 8 (figs. 5, 6, 8, and 9). For each geophone 

along profile 6c, we measured peak amplitudes at varying frequencies, and we recorded 

the time after the first arrival that the peak amplitude (velocity) was measured. In general, 

peak amplitudes typically were measured between 1 and 3 seconds (s) after the first 

arrival for S waves and about 0.2–1 s after the first arrival for P waves, suggesting that 

most of the high-amplitude energy likely resulted from seismic energy trapped within the 

fault zone. Plots of peak amplitude as a function of distance along profile 6c show that 

relatively high amplitudes are localized at multiple locations along the profile. In 

particular, relatively high amplitudes are located within a range of discrete distances, 

such as meters 16–18, 28–40, and 50–62, which approximately coincide with the faulttrace locations inferred from other data and discussed above in sections on P- and S-wave 

velocities, Vp/Vs ratios, and Poisson’s ratios. At higher frequencies, amplitude peaks 

generally become more localized (figs. 5, 6, 8, and 9), suggesting that individual nearsurface fault traces are imaged at progressively shallower depths with the increasingly 

higher frequencies. Peak ground velocities were about 2.5–3 times greater over the fault 

traces relative to the other areas of the seismic profile.

Recording Profile 8: Guided Waves, P-Wave Sensors

Guided waves were recorded along profile 8 using vertical and horizontal 

geophones along profile 8 and sources located at profile 6c (figs. 15 and 16). The peak 
12

amplitude energy was recorded between 0.1 and 0.5 s after the first arrivals on the 

vertical-component geophones (fig. 15). Because we observed this energy with verticalcomponent geophones, we theorize that the localized zones of high-amplitude energy 

correspond to P-wave seismic energy that is trapped within fault strands in the shallow 

subsurface. The locations of the highest amplitude energy vary from about meter 50 to 

about meter 28 of the seismic profile when the data are filtered from about 1 to 40 Hz. 

We interpret the lateral variation in peak amplitude as resulting from a northeast-dipping 

fault zone, whereby the lower frequencies respond to deeper parts of the fault, and the 

higher frequencies correlate with shallower and narrower parts of the fault. At higher 

frequencies, there are areas of peak amplitude centered near meters 5 and 53 of the 

seismic profile, consistent with the locations of known secondary smaller fault traces (fig. 

3) mapped by Schussler (1906). Peak ground velocities were about 6 to 8 times greater 

over the fault traces relative to the other areas of the seismic profile.

Recording Profile 8: Guided Waves, S-Wave Sensors

After recording the vertical-component guided waves along profile 8, we 

substituted horizontal-component geophones for the vertical-component geophones and 

repeated the shots located at profile 6. We measured peak amplitudes along profile 8 for 

each set of geophones at differing frequencies (figs. 16a–c). Typically, peak amplitude 

energy was recorded between 1 and 6 s after the first arrival, demonstrating that these are 

relatively slow-moving seismic waves, as expected of guided waves traveling along the 

fault zone. Although surface waves conceivably could generate the same strong 

amplitudes, surface waves would likely generate uniformly strong amplitudes along the 

entire recording array. Instead, we observed relatively high-amplitude seismic energy 

near the surface ruptures mapped by Schussler (1906). As observed with the verticalcomponent seismic energy, the apex of the peak amplitudes near the main surface rupture

varied laterally with frequency, such that the apex varied from west to east across the 

rupture zone and became more localized with increasing frequency. Strong peak 

amplitudes also were observed near meter 7 and near meter 50 for higher frequency data.

Peak ground velocities were about 3–5 times greater over the fault traces relative to the 

other areas of the seismic profile.

Recording Profile 9: Guided Waves, P-Wave Sensors

We recorded vertical-component guided waves along profile 9 for sources located 

at profile 8 (fig. 17). Because part of profile 9 was recorded within water, we limited the 

frequency content of the guided waves to values greater than 10 Hz to avoid the highamplitude, low-frequency waves in water. Generally, there are high peak amplitudes 

located between meters 25 and 90 (channels 5 and 18) and between meters 125 and 160 

(channels 35 and 32) of the seismic profile. The main fault trace, as indicated by 

geomorphology, was mapped at about meter 70 of the seismic profile. The guided waves 

suggest multiple fault traces along the seismic profile, with fault traces associated with 

the topographic high within the lake and at least one fault trace near the shoreline at about 

meter 150 (fig. 17). These relatively high amplitudes also coincide with the edges of lowvelocity zones below about 10 m depth, consistent with subsurface faulting in the deeper, 

higher velocity rocks. Peak ground velocities were about 6–10 times greater over the fault 

traces relative to the other areas of the seismic profile.
13

Discussion and Summary of Structures Along the Profiles

The seismic profiles show evidence of complex faulting within about 100 m of 

the 1906 surface rupture zone of the San Andreas Fault at San Andreas Lake. Our most 

detailed seismic information was at profile 6, which is our closest seismic imaging site to 

the intake system at San Andreas Lake. Along profile 6, our data indicate at least three

near-surface fault traces within about 20 m of the main 1906 surface rupture and an 

apparent fault zone located about 80 m east of the main 1906 surface rupture. A relatively 

wide zone of faulting near the main 1906 surface rupture also is consistent with 

observations by Schussler (1906) shortly after the 1906 San Francisco earthquake (fig. 

18). Our seismic indications of multiple near-surface fault traces included: 

Abrupt variations in the depth of P-wave velocity contours in the near surface, 

particularly the 1,500 m/s velocity contour, which also is consistent with the depth to 

the top of groundwater. Because most faults form barriers to groundwater flow, 

vertical variations in the depth to groundwater across faults, such as those observed, 

are expected.

Abrupt variations in deeper, higher-velocity P-wave velocity rocks, including lowvelocity zones. At depths of approximately 5–10 m below the surface, we observe 

multiple zones with an abrupt termination of the higher velocity rocks, which 

generally coincide with other indicators of faulting.

Abrupt topographic variations that coincide with the seismic variations described in item 

numbers 1 and 2. 

Abrupt variations in S-wave velocities; the presence of S-wave low-velocity zones that 

coincide with item numbers 1–3; or both. 

Areas of relatively high Vp/Vs and Poisson’s ratios that coincide with items numbers 1–

4. 

Geographical locations of high peak amplitudes, consistent with guided-wave energy 

traveling along the fault zones, which coincide geographically with item numbers 1–

5. 

Collectively, these indicators delineate several near-surface fault traces that 

extend over distances of at least 80 m from the main 1906 surface rupture. We also 

observed similar evidence of a wide (~80 m) area of faulting along profiles 8 and 9. For 

example, along profile 8, multiple mapped surface breaks associated with the 1906 San 

Francisco earthquake (Schussler, 1906) coincide with our seismic indicators described 

above. On the basis of the coincidence of the seismic indicators and Schussler’s map, we 

suggest three near-surface fault strands within 20 m of the main 1906 surface rupture 

along profile 8. Along profile 9, we have fewer data, but there is similar evidence for 

multiple zones of near-surface faulting. For example, in addition to the 1906 main surface 

rupture located near meter 70 of the seismic profile, our data suggest an additional nearsurface fault trace located about 80 m to the east and a third near-surface fault trace near 

the apex of the topographic high located within San Andreas Lake. Based on the apparent

fault geometry, the topographic high likely is a result of differential movement on the 

faults, resulting in a “push-up ridge.” 

Our study suggests that there are multiple near-surface fault traces within about 

80–100 m of the 1906 main surface rupture, and based on observations after the 1906 
14

earthquake (Schussler, 1906), these fault traces should be considered capable of moving 

during future earthquakes (fig. 18). Furthermore, differential movement on sub-parallel

fault strands can result in complex shearing involving both compressive and extensional 

stresses. Similar shearing appears to have occurred at the southern end of San Andreas 

Lake at the gatewell structure during the 1906 San Francisco earthquake (see fig. 3). 

There, the gatewell was located between two faults, and the structure was transformed

from a circular structure to a northwest-southeast-oriented oblong structure after the 

earthquake (Schussler, 1906). Because our studies did not extend beyond about 100 m 

from the 1906 main surface rupture, we cannot determine if there are additional 

secondary faults that extend beyond the area of our study. Engineering efforts and 

probabilistic seismic hazard assessment studies should, however, address the possibility 

of additional fault traces beyond 100 m from the main 1906 surface rupture and the types 

of shearing that might ensue from such fault geometries. 

The guided-wave data show that ground shaking is enhanced over the individual 

fault traces, varying with the frequency of the seismic data and the wave type (P versus 

S). S-wave ground shaking increases by about 5–6 times at the fault traces relative to 

areas outside the fault zone, and P-wave shaking appears to increase by about 3–10 times

across the same fault traces. In addition to the surface rupture hazard associated with 

large-magnitude earthquakes, these data suggest (assuming linearity) that such strong 

shaking may also pose a hazard to built structures that extend across the fault traces.

Acknowledgments

This work was jointly funded by the San Francisco Public Utilities Commission 

(SFPUC) and the U.S. Geological Survey’s Earthquake Hazards Program through a 

Cooperative Research and Development Agreement (CRADA). We thank the SFPUC for 

field site access. We especially thank Leroy Gullette and his team for CRADA assistance, 

helpful suggestions, and field assistance. Thanks to John Tinsley and John Reeder for 

helpful reviews. 

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17

Figure 1. (a) Google EarthTM photograph showing the locations of seismic profiles 6a, 6b, 6c, 8, 

and 9 that were acquired along the eastern shore of San Andreas Lake in 2008, 2009 and 

2011. The northeast-southwest-oriented yellow and green lines show the locations of the 

seismic profiles. The thin red lines trending through the seismic profiles are the mapped 

(California Holocene Fault database) locations of the principal surface traces of the San 

Andreas Fault. (b) Same figure as shown in figure 1a, with the locations of small charges 

(stars) used to generate guided waves are shown.
18

Figure 1. —Continued 
19

Figure 2. Google EarthTM photograph showing seismic profiles 6a, 6b, and 6c (yellow and green 

lines). The approximate locations of faults inferred from geomorphology are shown as the thin 

red lines (California Holocene Fault database). White arrows also point to the mapped faults.

The locations of faults imaged seismically are shown as the short and thicker red line 

segments. Multiple near-surface faults are imaged near the main 1906 surface rupture and at 

least one additional fault is imaged about 80 meters northeast of the 1906 surface rupture 

area.
20

Figure 3. (a) Google EarthTM photograph showing seismic profile 8 (yellow line). The approximate 

locations of faults inferred (mapped) from geomorphology are shown as the thin red lines 

(Holocene Fault database). The white arrows also point to the mapped faults. Faults imaged 

seismically and mapped by Schussler (1906) are shown as the shorter and thicker red lines.

(b) Sketch map of faulting that occurred on the eastern shore of San Andreas Lake during the 

1906 ~magnitude 7.9 San Francisco earthquake (map by Schussler, 1906). Faulting occurred 

over at least an ~35-meter-wide area, with multiple traces of surface rupture. Note that the 

structures in the central fault area were deformed. The thick red line with distance scales 

shows the location of our seismic profile 8.
21

Figure 3.—Continued 
22

Figure 4. Google EarthTM photograph showing seismic profile 9 (yellow line). The approximate 

locations of faults inferred from geomorphology are shown as the thin red lines (Holocene Fault 

database). White arrows also point to the mapped faults. Faults imaged seismically are shown 

as the thicker red lines.
23

Figure 5. (a) Refraction tomography P-wave velocity models for profiles 6 (6a, b, c). The data for 

profile 6a were acquired in 2008, profile 6b in 2009, and profile 6c in 2011. The lake level was 

progressively lowered during each year of acquisition. The general location (based on 

geomorphology) of the main surface rupture area of the San Andreas Fault during the 1906 

~magnitude 7.9 San Francisco earthquake is shown along profiles 6b and 6c. The seismically 

imaged fault locations are shown by the arrows. We interpret an additional “East Fault Zone” 

along profile 6a, based on seismic velocity and topographic anomalies. The 1,500 meter per 

second velocity contour is shown in white. A plot of peak amplitudes (guided waves) as a 

function of distance along profile 6c is shown above profile 6c. The peak amplitudes were 

measured on vertical component geophones. (b) Same plot as shown in figure 5a, except 

profile 6b has been removed to show details of profile 6c.
24

Figure 5.—Continued. 
25

Figure 6. (a) Refraction tomography S-wave velocity models for profiles 6 (6a, b, c) from data 

acquired in 2008 (profile 6a), 2009 (profile 6b) and 2011 (profile 6c). The general location 

(based on geomorphology) of the main surface rupture area of the San Andreas Fault during 

the 1906 ~magnitude 7.9 San Francisco earthquake is shown along profiles 6b and 6c. The 

seismically imaged fault locations are shown by the arrows. We interpret an additional “East 

Fault Zone” along profile 6a on the basis of offset velocity anomalies, low-velocity zones, and 

altitude variations. The seismic profiles were acquired with varying degrees of water saturation 

and solidification of surface materials. Peak-amplitude measurements of vertical-component 

seismic (guided wave) data are shown along profile 6a. The highest amplitudes coincide with 

the seismic velocity indicators of faulting and the interpreted (on the basis of geomorphology) 

main surface rupture area associated with the 1906 magnitude 7.9 San Francisco earthquake. 

(b) Same plot as shown in figure 6a, except profile 6b has been removed to show details of 

profile 6c.
26

Figure 6.—Continued. 
27

Figure 7. Photograph showing area near profile 6c. The flags on the left side of the photograph

show the locations of shot and recording sites along the seismic profile. The surface materials 

along most of profile 6c consisted of highly brecciated rocks, including serpentinite (see inset). 
28

Figure 8. (a) P-wave velocity divided by S-wave velocity (Vp/Vs) models for profile 6 (a, b, c), 

developed from the refraction tomography P- and S-wave models of figures 5 and 6. Relatively 

high near-surface Vp/Vs ratios correlate with known fault zones when the near-surface 

materials are composed of consolidated sediments or hard rocks (Catchings and others, in 

prep.). High Vp/Vs ratios are observed at the main surface rupture zone along profiles 6b and 

6c, and along profile 6a near meters 45–50. At depth along profile 6b and 6c, the high Vp/Vs 

ratios become narrow, extending to the base of the model near the central 1906 surface 

rupture area. Peak amplitudes measured along profile 6c approximately coincide with areas of 

high Vp/Vs ratios. The seismically imaged fault locations are shown by the arrows. (b) Same 

plot as shown in figure 8a, except profile 6b has been removed to show details of profile 6c.
29

Figure 9. (a) Poisson’s ratio (PR) models for profile 6, developed from the refraction tomography 

P- and S-wave models of figures 5 and 6. PR is most sensitive to the presence of groundwater, 

and the model points out anomalous areas where groundwater is likely most affected by faults.

The greatest changes in near-surface PR largely coincide with the inferred areas of nearsurface faulting. At depths ranging from a few meters along profile 6b and 6c to about 5–10 m 

along profile 6c, the highest values of PR largely follow the 1,500 meter per second velocity 

contour. The seismically imaged fault locations are shown by the arrows. (b) Same plot as 

shown in figure 9a, except profile 6b has been removed to show details of profile 6c.
30

Figure 10. Refraction tomography P-wave velocity model for profile 8 with the locations of surface 

ruptures (at red arrows) mapped by Schussler (1906). For velocities greater than 1,500 meter 

per second, there are abrupt lateral changes in velocity west of the surface ruptures. The 

seismically imaged fault locations are shown by the arrows. 
31

Figure 11. Refraction tomography S-wave velocity model for profile 8 with the locations of surface 

ruptures (at red arrows) mapped by Schussler (1906). A prominent low-velocity zone is 

concentrated along the eastern surface rupture area, and an apparent west-dipping structure 

coincides with the westernmost surface rupture. The seismically imaged fault locations are 

shown by the arrows.
32

Figure 12. P-wave velocity divided by S-wave velocity (Vp/Vs) model for profile 8 developed from 

the refraction tomography P- and S-waves models of figures 10 and 11. The highest Vp/Vs 

ratios occur at about 5–10 m below the surface, but localized, near-surface, high Vp/Vs ratios 

of ~2 coincide with the 1906 main and westernmost surface ruptures. Unconsolidated 

sediments are present in the near surface along the entire seismic profile, resulting in 

particularly high Vp/Vs ratios in fault zones. The seismically imaged fault locations are shown 

by the arrows.
33

Figure 13. Poisson’s Ratio (PR) model for profile 8 developed from the refraction tomography Pand S-waves models of figures 10 and 11. The high values of PR largely follow the trend of the 

1,500 meter per second velocity contour (top of groundwater). There are relatively high PR 

values near the 1906 main and westernmost surface ruptures. The seismically imaged fault 

locations are shown by the arrows.
34

Figure 14. Refraction tomography P-wave velocity model for profile 9. The 1906 main surface 

rupture area is shown near meter 70, and two additional rupture zones (at meters 30 and 145) 

are inferred from this study. Higher velocities are discontinuous or disrupted near the inferred 

faults. The seismically imaged fault locations are shown by the arrows.
35

Figure 15. A comparison of peak-amplitude (horizontal-component) guided waves recorded along 

profile 8 with the S-wave velocity model for profile 6. The highest amplitudes coincide with the 

surface rupture areas mapped by Schussler (1906) at predominant frequencies of (a) 5 hertz 

(Hz), (b) 4 Hz, and (c) 2 Hz. (d) However, at very low frequencies (1 Hz), the peak amplitudes 

are largely concentrated over the deeper low-velocity (fault) zone. The seismically imaged fault 

locations are shown by the arrows.
36

Figure 15.—Continued. 
37

Figure 15.—Continued. 
38

Figure 15.—Continued. 
39

Figure 16. A comparison of peak-amplitude (vertical-component) guided waves recorded along 

profile 8 with the P-wave velocity model for profile 6. The highest amplitudes coincide with the 

surface rupture areas mapped by Schussler (1906) at predominant frequencies of (a) 15 hertz 

(Hz), (b) 20 Hz, and (c) 30 Hz. The seismically imaged fault locations are shown by the arrows.
40

Figure 16.—Continued. 
41

Figure 16.—Continued. 
42

Figure 17. A comparison of peak-amplitude (vertical-component) guided waves recorded along 

profile 9 with the P-wave velocity model for profile 9. The highest amplitudes coincide with the 

surface rupture area inferred from geomorphology at predominant frequencies of (a) 10 hertz 

(Hz), (b) 20 Hz, and (c) 30 Hz. The seismically imaged fault locations are shown by the arrows.
43

Figure 17.—Continued. 
44

Figure 17.—Continued. 
45

Figure 18. Map from Schussler (1906) showing off-fault displacements associated with the 1906 

San Francisco earthquake at three separate locations (profiles L, N, and N’) just south of San 

Andreas Lake (SAL). Profile N’ was located at the northern end of Crystal Springs Reservoir 

(CSR), ~ 2.2 kilometers south of the southern end of SAL. Profile N was located between CSR 

and SAL, ~1.1 kilometers south of the southern end of SAL. Profile L was located between 

CSR and SAL, ~0.55 kilometers south of the southern end of SAL. There were significant 

lateral displacements (~ 4 m) of fences, with the principal area of displacement as far as 35 

meters from the surface rupture associated with the main surface trace of the San Andreas 

Fault.
46

Appendix 1. Acquisition and Geometry for Profile 6a

Sta. # Latitude Longitude Northing Easting Altitude Local X Local Y Local Z

1 37.6005873 -122.4273313 4161655 550550.47 102.69 0 0.56 0

2 37.60059162 -122.4273094 4161655.49 550552.4 102.7 1.98 0.71 0.01

3 37.60059045 -122.4272874 4161655.37 550554.34 102.77 3.88 0.26 0.08

4 37.60059253 -122.4272654 4161655.62 550556.28 102.76 5.83 0.17 0.07

5 37.60059578 -122.4272426 4161655.99 550558.29 102.75 7.88 0.2 0.06

6 37.60059854 -122.4272173 4161656.31 550560.53 102.84 10.13 0.13 0.15

7 37.60060077 -122.4271968 4161656.57 550562.33 102.88 11.95 0.08 0.19

8 37.6006043 -122.4271741 4161656.97 550564.33 102.86 13.99 0.13 0.17

9 37.60060591 -122.4271528 4161657.16 550566.21 102.89 15.88 0 0.2

10 37.60060944 -122.4271295 4161657.57 550568.26 102.91 17.97 0.05 0.22

11 37.60061215 -122.4271076 4161657.88 550570.2 102.93 19.93 0.02 0.24

12 37.60061422 -122.4270857 4161658.12 550572.13 102.92 21.88 -0.07 0.23

13 37.60061773 -122.4270639 4161658.52 550574.05 102.89 23.84 0 0.2

14 37.60062135 -122.4270412 4161658.93 550576.06 102.91 25.89 0.06 0.22

15 37.60062235 -122.4270186 4161659.06 550578.04 102.97 27.87 -0.16 0.28

16 37.60062622 -122.4269968 4161659.5 550579.97 103 29.84 -0.05 0.31

17 37.60062901 -122.4269746 4161659.82 550581.92 103.03 31.82 -0.07 0.34

18 37.60063163 -122.4269525 4161660.12 550583.88 103.07 33.8 -0.1 0.38

19 37.60063443 -122.4269303 4161660.45 550585.84 103.1 35.79 -0.12 0.41

20 37.60063723 -122.426908 4161660.77 550587.8 103.13 37.77 -0.14 0.44

21 37.60063743 -122.4268847 4161660.8 550589.86 103.24 39.81 -0.45 0.55

22 37.60064051 -122.4268619 4161661.16 550591.87 103.52 41.85 -0.45 0.83

23 37.60064391 -122.426841 4161661.55 550593.71 103.69 43.73 -0.38 1

24 37.60064564 -122.426818 4161661.75 550595.74 103.99 45.77 -0.52 1.3

25 37.60064745 -122.4267953 4161661.96 550597.74 104.06 47.77 -0.66 1.37

26 37.60065043 -122.4267734 4161662.3 550599.67 104.33 49.74 -0.65 1.64

27 37.60065349 -122.4267514 4161662.66 550601.61 104.61 51.71 -0.63 1.92

28 37.60065655 -122.4267294 4161663.01 550603.55 104.88 53.68 -0.62 2.19

29 37.60065962 -122.4267074 4161663.36 550605.49 105.15 55.65 -0.6 2.46

30 37.60066268 -122.4266856 4161663.71 550607.41 105.42 57.61 -0.59 2.73

31 37.60066574 -122.4266636 4161664.06 550609.35 105.7 59.58 -0.57 3.01

32 37.60066872 -122.4266416 4161664.41 550611.29 105.97 61.55 -0.56 3.28

33 37.60067187 -122.4266197 4161664.77 550613.22 106.24 63.52 -0.54 3.55

34 37.60067484 -122.4265977 4161665.11 550615.16 106.51 65.49 -0.53 3.82

35 37.600678 -122.4265757 4161665.47 550617.1 106.79 67.46 -0.51 4.1

36 37.60068097 -122.4265537 4161665.81 550619.05 107.06 69.43 -0.5 4.37

37 37.60068413 -122.4265318 4161666.17 550620.98 107.33 71.4 -0.48 4.64

38 37.6006871 -122.4265098 4161666.52 550622.92 107.6 73.37 -0.47 4.91

39 37.60069025 -122.4264878 4161666.88 550624.86 107.88 75.34 -0.45 5.19

40 37.60069323 -122.4264659 4161667.22 550626.79 108.15 77.3 -0.44 5.46
47

41 37.60069629 -122.426444 4161667.57 550628.72 108.42 79.27 -0.42 5.73

42 37.60069935 -122.426422 4161667.92 550630.66 108.69 81.24 -0.41 6

43 37.60070242 -122.4264 4161668.27 550632.6 108.97 83.21 -0.39 6.28

44 37.60070548 -122.4263781 4161668.63 550634.53 109.24 85.18 -0.38 6.55

45 37.60070945 -122.4263555 4161669.08 550636.52 109.64 87.21 -0.27 6.95

46 37.60071161 -122.4263337 4161669.33 550638.44 109.85 89.15 -0.35 7.16

47 37.60071576 -122.4263118 4161669.8 550640.37 110.2 91.13 -0.21 7.51

48 37.60071971 -122.4262903 4161670.25 550642.27 110.49 93.08 -0.09 7.8

49 37.60072224 -122.426268 4161670.55 550644.24 110.9 95.07 -0.14 8.21

50 37.60072583 -122.4262473 4161670.95 550646.06 111.06 96.94 -0.05 8.37

51 37.60072916 -122.4262257 4161671.33 550647.97 111.18 98.88 0 8.49

52 37.6007334 -122.4262033 4161671.82 550649.94 111.47 100.91 0.14 8.78

53 37.60073647 -122.4261808 4161672.17 550651.93 111.89 102.93 0.15 9.2

54 37.60073821 -122.4261623 4161672.37 550653.55 112.17 104.56 0.07 9.48

55 37.60074377 -122.4261367 4161673 550655.82 112.76 106.9 0.3 10.07

56 37.60074609 -122.4261163 4161673.27 550657.61 112.95 108.72 0.26 10.26

57 37.60074944 -122.4260934 4161673.66 550659.63 113.26 110.77 0.3 10.57

58 37.60075368 -122.426071 4161674.14 550661.61 113.43 112.8 0.43 10.74

59 37.60075594 -122.4260486 4161674.4 550663.58 113.49 114.79 0.36 10.8

Appendix 2. Acquisition and Geometry for Profile 6b

Sta # Latitude Longitude Northing Easting

 

Altitude Local X Local Y Local Z

1 37.60053137 -122.4278985 4161648.49 550500.44 97.56 0 0.22 0

2 37.60053239 -122.4278863 4161648.61 550501.51 97.85 1.08 0.18 0.29

3 37.6005336 -122.427876 4161648.75 550502.42 97.62 2 0.18 0.06

4 37.60053607 -122.4278652 4161649.03 550503.37 97.87 2.98 0.32 0.31

5 37.60053602 -122.4278538 4161649.03 550504.38 97.71 3.98 0.18 0.15

6 37.60053568 -122.42784 4161649 550505.6 97.93 5.18 -0.03 0.37

7 37.60053843 -122.427831 4161649.31 550506.39 97.72 6.01 0.16 0.16

8 37.60053838 -122.4278209 4161649.31 550507.28 97.75 6.89 0.03 0.19

9 37.60054013 -122.4278086 4161649.51 550508.37 97.88 8 0.07 0.32

10 37.60054107 -122.4277981 4161649.62 550509.29 97.91 8.92 0.05 0.35

11 37.60054201 -122.4277878 4161649.73 550510.2 97.93 9.84 0.02 0.37

12 37.60054258 -122.4277758 4161649.8 550511.26 98.13 10.9 -0.06 0.57

13 37.60054442 -122.4277642 4161650.01 550512.28 98.24 11.94 0 0.68

14 37.60054535 -122.4277531 4161650.12 550513.26 98.38 12.92 -0.04 0.82

15 37.60054666 -122.4277429 4161650.27 550514.16 98.6 13.83 -0.02 1.04

16 37.60054822 -122.4277298 4161650.45 550515.32 98.85 15.01 -0.01 1.29

17 37.60054788 -122.4277172 4161650.42 550516.43 98.93 16.1 -0.2 1.37

18 37.60054919 -122.427708 4161650.57 550517.24 99.09 16.93 -0.17 1.53
48

19 37.60055157 -122.4276968 4161650.84 550518.23 99 17.94 -0.05 1.44

20 37.60055161 -122.4276852 4161650.85 550519.25 99.29 18.95 -0.19 1.73

21 37.60055335 -122.427674 4161651.05 550520.24 99.36 19.96 -0.13 1.8

22 37.60055411 -122.4276629 4161651.14 550521.22 99.61 20.95 -0.19 2.05

23 37.60055657 -122.4276503 4161651.42 550522.33 99.29 22.09 -0.07 1.73

24 37.60055931 -122.4276394 4161651.73 550523.29 99.86 23.08 0.09 2.3

25 37.60055854 -122.4276289 4161651.65 550524.22 99.75 23.99 -0.12 2.19

26 37.6005594 -122.4276196 4161651.75 550525.04 99.51 24.81 -0.14 1.95

27 37.60056114 -122.4276074 4161651.95 550526.11 99.77 25.9 -0.1 2.21

28 37.6005619 -122.4275955 4161652.04 550527.16 99.97 26.95 -0.16 2.41

29 37.60056428 -122.4275842 4161652.31 550528.16 99.8 27.98 -0.04 2.24

30 37.60056242 -122.427573 4161652.11 550529.15 99.79 28.93 -0.38 2.23

31 37.60056516 -122.427562 4161652.42 550530.12 99.87 29.94 -0.22 2.31

32 37.60056799 -122.4275511 4161652.74 550531.08 99.95 30.93 -0.04 2.39

33 37.60056929 -122.4275394 4161652.89 550532.11 100 31.98 -0.04 2.44

34 37.60056941 -122.427528 4161652.91 550533.12 100.54 32.98 -0.17 2.98

35 37.60057207 -122.4275181 4161653.21 550533.99 100.26 33.88 0 2.7

36 37.60057354 -122.427506 4161653.38 550535.06 100.35 34.96 0.01 2.79

37 37.60057557 -122.4274961 4161653.61 550535.93 100.66 35.86 0.11 3.1

38 37.6005765 -122.4274846 4161653.72 550536.94 100.49 36.87 0.08 2.93

39 37.60057752 -122.4274726 4161653.84 550538 100.51 37.94 0.04 2.95

40 37.60057873 -122.4274609 4161653.98 550539.03 100.54 38.98 0.03 2.98

41 37.60057931 -122.42745 4161654.05 550540 100.67 39.95 -0.04 3.11

42 37.60058097 -122.4274396 4161654.24 550540.91 101.06 40.88 0.01 3.5

43 37.60058154 -122.4274277 4161654.31 550541.96 101.06 41.93 -0.07 3.5

44 37.60058934 -122.4274182 4161655.18 550542.8 101.19 42.88 0.67 3.63

45 37.60059217 -122.4274068 4161655.5 550543.8 101.28 43.92 0.84 3.72

46 37.60058652 -122.4273954 4161654.88 550544.81 100.96 44.83 0.08 3.4

47 37.60058656 -122.4273838 4161654.89 550545.83 101.34 45.84 -0.06 3.78

48 37.60058704 -122.4273725 4161654.95 550546.83 101.48 46.84 -0.15 3.92

49 37.60058969 -122.4273606 4161655.25 550547.88 102.03 47.92 0 4.47

50 37.60059036 -122.4273498 4161655.33 550548.83 102.07 48.87 -0.06 4.51

51 37.60059166 -122.4273397 4161655.48 550549.72 102.03 49.77 -0.04 4.47

52 37.60059332 -122.4273284 4161655.67 550550.72 101.92 50.79 0 4.36

53 37.60059443 -122.4273166 4161655.8 550551.76 102.32 51.84 -0.02 4.76

54 37.60059511 -122.4273072 4161655.88 550552.59 101.94 52.67 -0.06 4.38

55 37.60059612 -122.4272934 4161656 550553.81 101.94 53.9 -0.12 4.38

56 37.60059769 -122.4272828 4161656.18 550554.74 102 54.84 -0.08 4.44

57 37.60059909 -122.4272722 4161656.34 550555.68 102.04 55.8 -0.06 4.48

58 37.60060057 -122.4272616 4161656.51 550556.61 102.08 56.74 -0.03 4.52

59 37.60060231 -122.4272493 4161656.71 550557.7 101.98 57.85 0.01 4.42

60 37.60060316 -122.4272392 4161656.81 550558.59 101.96 58.74 -0.02 4.4
49

Appendix 3. Acquisition and Geometry for Profile 6c Sta. # Latitude Longitude Northing Easting Altitude Local X Local Y Local Z

1 37.60051032 -122.4281125 4161646.04 550481.56 99.44 0 0.69 0.06

2 37.60051162 -122.4281014 4161646.19 550482.54 99.52 0.99 0.68 0.14

3 37.60051292 -122.4280902 4161646.34 550483.53 99.6 1.99 0.66 0.22

4 37.60051422 -122.428079 4161646.49 550484.52 99.69 2.99 0.65 0.31

5 37.60051551 -122.428068 4161646.64 550485.49 99.77 3.98 0.63 0.39

6 37.6005169 -122.4280566 4161646.8 550486.49 99.85 4.99 0.61 0.47

7 37.6005182 -122.4280455 4161646.95 550487.47 99.93 5.98 0.59 0.55

8 37.6005195 -122.4280343 4161647.1 550488.46 100.01 6.98 0.58 0.63

9 37.60052223 -122.4280218 4161647.41 550489.56 100.16 8.11 0.42 0.78

10 37.60052468 -122.4280074 4161647.69 550490.83 100.3 9.41 0.32 0.92

11 37.60052554 -122.4279979 4161647.79 550491.67 100.41 10.25 0.33 1.03

12 37.60052757 -122.427989 4161648.02 550492.45 100.48 11.06 0.21 1.1

13 37.6005284 -122.4279752 4161648.12 550493.67 100.54 12.28 0.28 1.16

14 37.60052944 -122.4279662 4161648.24 550494.46 100.64 13.08 0.26 1.26

15 37.60053074 -122.4279546 4161648.39 550495.49 100.75 14.12 0.26 1.37

16 37.60053194 -122.4279419 4161648.53 550496.61 100.81 15.25 0.27 1.43

17 37.60053325 -122.4279328 4161648.68 550497.41 100.87 16.06 0.23 1.49

18 37.60053417 -122.4279188 4161648.79 550498.64 100.97 17.29 0.29 1.59

19 37.60053611 -122.4279102 4161649.01 550499.4 101.03 18.08 0.17 1.65

20 37.60053768 -122.4278984 4161649.19 550500.44 101.08 19.13 0.13 1.7

21 37.60053916 -122.4278884 4161649.36 550501.32 101.12 20.03 0.09 1.74

22 37.60054037 -122.427877 4161649.5 550502.33 101.21 21.05 0.08 1.83

23 37.60054184 -122.4278654 4161649.67 550503.35 101.25 22.08 0.05 1.87

24 37.60054377 -122.4278542 4161649.89 550504.34 101.3 23.09 -0.03 1.92

25 37.6005448 -122.4278429 4161650.01 550505.34 101.34 24.1 -0.01 1.96

26 37.60054618 -122.4278303 4161650.17 550506.45 101.46 25.22 -0.02 2.08

27 37.60054703 -122.4278203 4161650.27 550507.33 101.49 26.11 0 2.11

28 37.60054914 -122.4278098 4161650.51 550508.26 101.56 27.06 -0.11 2.18

29 37.60055044 -122.4277989 4161650.66 550509.22 101.6 28.03 -0.13 2.22

30 37.60055246 -122.4277871 4161650.89 550510.26 101.7 29.09 -0.22 2.32

31 37.60055341 -122.4277777 4161651 550511.09 101.75 29.93 -0.21 2.37

32 37.60055362 -122.4277661 4161651.03 550512.11 101.85 30.94 -0.11 2.47

33 37.60055527 -122.4277535 4161651.22 550513.22 101.99 32.07 -0.14 2.61

34 37.60055719 -122.4277409 4161651.44 550514.33 102.19 33.2 -0.21 2.81

35 37.6005594 -122.4277303 4161651.69 550515.27 102.28 34.16 -0.33 2.9

36 37.60055917 -122.4277206 4161651.67 550516.12 102.35 35 -0.2 2.97

37 37.60056047 -122.4277108 4161651.82 550516.99 102.43 35.89 -0.23 3.05

38 37.6005614 -122.4276983 4161651.93 550518.09 102.56 36.99 -0.19 3.18
50

39 37.60056162 -122.4276881 4161651.96 550518.99 102.63 37.89 -0.09 3.25

40 37.60056372 -122.4276749 4161652.2 550520.15 102.73 39.07 -0.18 3.35

41 37.60056458 -122.4276655 4161652.3 550520.98 102.75 39.9 -0.16 3.37

42 37.60056659 -122.4276533 4161652.53 550522.06 102.9 41.01 -0.24 3.52

43 37.60056752 -122.4276409 4161652.64 550523.15 102.96 42.1 -0.2 3.58

44 37.60056847 -122.4276308 4161652.75 550524.04 103.08 43 -0.19 3.7

45 37.60056922 -122.4276191 4161652.84 550525.08 103.26 44.04 -0.14 3.88

46 37.60056926 -122.4276089 4161652.85 550525.98 103.17 44.93 -0.03 3.79

47 37.60057155 -122.4275966 4161653.11 550527.06 103.26 46.04 -0.14 3.88

48 37.60057258 -122.4275862 4161653.23 550527.98 103.33 46.97 -0.13 3.95

49 37.60057495 -122.427573 4161653.5 550529.14 103.44 48.15 -0.24 4.06

50 37.60057598 -122.4275625 4161653.62 550530.07 103.51 49.09 -0.24 4.13

51 37.6005771 -122.4275524 4161653.75 550530.96 103.57 49.99 -0.24 4.19

52 37.60057903 -122.4275416 4161653.97 550531.91 103.64 50.96 -0.33 4.26

53 37.60057951 -122.4275294 4161654.03 550532.99 103.74 52.04 -0.25 4.36

54 37.60058126 -122.4275185 4161654.23 550533.95 103.81 53.02 -0.31 4.43

55 37.60058283 -122.427508 4161654.41 550534.87 103.86 53.95 -0.37 4.48

56 37.6005835 -122.4274967 4161654.49 550535.87 103.93 54.95 -0.31 4.55

57 37.6005839 -122.4274863 4161654.54 550536.79 103.99 55.87 -0.24 4.61

58 37.60058573 -122.4274744 4161654.75 550537.84 104.08 56.94 -0.3 4.7

59 37.60058613 -122.4274636 4161654.8 550538.79 104.16 57.89 -0.22 4.78

60 37.60058752 -122.427452 4161654.96 550539.81 104.22 58.92 -0.24 4.84

61 37.60058854 -122.4274401 4161655.08 550540.86 104.27 59.98 -0.22 4.89

62 37.60058948 -122.4274293 4161655.19 550541.82 104.33 60.94 -0.2 4.95

63 37.60059205 -122.4274189 4161655.48 550542.73 104.41 61.88 -0.36 5.03

64 37.60059361 -122.4274066 4161655.66 550543.82 104.52 62.99 -0.39 5.14

65 37.60059446 -122.4273959 4161655.76 550544.76 104.58 63.93 -0.37 5.2

66 37.60059594 -122.4273849 4161655.93 550545.73 104.71 64.92 -0.4 5.33

67 37.60059688 -122.4273743 4161656.04 550546.67 104.94 65.86 -0.38 5.56

68 37.600596 -122.4273608 4161655.95 550547.86 105.5 67.03 -0.13 6.12

69 37.60059768 -122.4273534 4161656.14 550548.51 105.51 67.7 -0.23 6.13

70 37.60059978 -122.4273409 4161656.38 550549.61 105.53 68.82 -0.32 6.15

71 37.60060044 -122.4273281 4161656.46 550550.74 105.54 69.95 -0.25 6.16

72 37.60059966 -122.4273169 4161656.38 550551.73 105.55 70.92 -0.03 6.17

73 37.60059943 -122.4273064 4161656.36 550552.66 105.58 71.84 0.11 6.2

74 37.60060001 -122.4272946 4161656.43 550553.7 105.62 72.88 0.18 6.24

75 37.60060168 -122.4272859 4161656.62 550554.47 105.62 73.67 0.1 6.24

76 37.60060369 -122.4272742 4161656.85 550555.5 105.6 74.72 0.01 6.22

77 37.60060265 -122.427263 4161656.74 550556.49 105.68 75.69 0.26 6.3

78 37.60060277 -122.4272514 4161656.76 550557.51 105.68 76.7 0.37 6.3

79 37.60060307 -122.4272389 4161656.8 550558.61 105.7 77.8 0.48 6.32

80 37.60060446 -122.4272277 4161656.96 550559.6 105.72 78.8 0.46 6.34

81 37.60060619 -122.4272141 4161657.16 550560.8 105.73 80.02 0.42 6.35
51

82 37.60060821 -122.4272029 4161657.39 550561.79 105.72 81.03 0.33 6.34

83 37.60060763 -122.4271933 4161657.33 550562.64 105.76 81.86 0.5 6.38

84 37.60060856 -122.4271823 4161657.44 550563.61 105.79 82.84 0.53 6.41

85 37.60060905 -122.4271709 4161657.5 550564.61 105.81 83.84 0.6 6.43

86 37.60060981 -122.427161 4161657.59 550565.49 105.81 84.72 0.63 6.43

87 37.60061102 -122.4271506 4161657.73 550566.4 105.86 85.64 0.62 6.48

88 37.60061069 -122.4271368 4161657.7 550567.62 105.82 86.85 0.81 6.44

Appendix 4. Acquisition and Geometry for Profile 8 Sta # Latitude Longitude Northing Easting Altitude Local X Local Y Local Z

1 37.58747374 -122.416867 4160205.79 551483.21 98.08 0 -0.31 0

2 37.58747657 -122.4168551 4160206.11 551484.26 98.2 1.08 -0.08 0.12

3 37.58748067 -122.4168454 4160206.57 551485.11 98.4 2.04 -0.07 0.32

4 37.58748485 -122.4168357 4160207.04 551485.97 98.69 3.02 -0.06 0.61

5 37.58749021 -122.416825 4160207.64 551486.91 98.97 4.14 -0.13 0.89

6 37.58749332 -122.416816 4160207.99 551487.7 99.18 5 -0.05 1.1

7 37.58749696 -122.4168056 4160208.4 551488.62 99.41 6 0.04 1.33

8 37.5874997 -122.4167944 4160208.71 551489.6 99.7 7.01 0.25 1.62

9 37.58750544 -122.4167873 4160209.35 551490.23 99.9 7.87 -0.01 1.82

10 37.58750988 -122.4167751 4160209.85 551491.3 100 9.05 0.08 1.92

11 37.58751407 -122.4167653 4160210.32 551492.16 100.16 10.03 0.08 2.08

12 37.58751816 -122.4167533 4160210.78 551493.22 100.48 11.18 0.2 2.4

13 37.58752191 -122.4167459 4160211.2 551493.87 100.57 11.95 0.14 2.49

14 37.58752672 -122.4167361 4160211.74 551494.73 100.72 12.96 0.09 2.64

15 37.58753208 -122.416726 4160212.34 551495.62 100.95 14.03 0 2.87

16 37.58753646 -122.4167176 4160212.83 551496.36 101.09 14.92 -0.07 3.01

17 37.58754101 -122.4167087 4160213.34 551497.14 101.28 15.85 -0.13 3.2

18 37.58754574 -122.4166991 4160213.87 551497.99 101.4 16.85 -0.19 3.32

19 37.58754867 -122.4166891 4160214.2 551498.87 101.49 17.78 -0.04 3.41

20 37.5875533 -122.4166783 4160214.72 551499.82 101.55 18.86 -0.04 3.47

21 37.58755667 -122.416668 4160215.1 551500.72 101.52 19.83 0.07 3.44

22 37.5875605 -122.4166573 4160215.53 551501.67 101.46 20.87 0.15 3.38

23 37.58756658 -122.4166477 4160216.21 551502.51 101.44 21.93 -0.03 3.36

24 37.58757086 -122.4166388 4160216.69 551503.29 101.42 22.85 -0.07 3.34

25 37.5875745 -122.416628 4160217.1 551504.24 101.39 23.88 0.03 3.31

26 37.58757878 -122.4166178 4160217.58 551505.14 101.36 24.9 0.05 3.28

27 37.58758197 -122.4166074 4160217.94 551506.06 101.35 25.88 0.18 3.27

28 37.58758734 -122.4165986 4160218.54 551506.83 101.3 26.84 0.03 3.22

29 37.5875908 -122.4165873 4160218.93 551507.83 101.32 27.91 0.18 3.24

30 37.58759562 -122.416578 4160219.47 551508.64 101.34 28.88 0.1 3.26

31 37.5876008 -122.4165689 4160220.05 551509.44 101.32 29.86 -0.02 3.24
52

32 37.5876048 -122.4165584 4160220.5 551510.37 101.33 30.89 0.04 3.25

33 37.58760926 -122.416549 4160221 551511.19 101.35 31.85 0 3.27

34 37.58761363 -122.4165386 4160221.49 551512.11 101.4 32.89 0.02 3.32

35 37.58761754 -122.4165281 4160221.93 551513.03 101.42 33.91 0.08 3.34

36 37.58762318 -122.4165193 4160222.56 551513.81 101.43 34.9 -0.09 3.35

37 37.58762736 -122.4165093 4160223.03 551514.69 101.43 35.9 -0.07 3.35

38 37.58763056 -122.4164993 4160223.39 551515.57 101.49 36.84 0.04 3.41

39 37.58763466 -122.4164892 4160223.85 551516.46 101.49 37.84 0.07 3.41

40 37.5876392 -122.416479 4160224.36 551517.35 101.5 38.87 0.06 3.42

41 37.58764366 -122.4164693 4160224.86 551518.21 101.54 39.86 0.04 3.46

42 37.58764929 -122.4164596 4160225.49 551519.06 101.55 40.91 -0.1 3.47

43 37.58765493 -122.4164507 4160226.12 551519.84 101.56 41.9 -0.26 3.48

44 37.58765776 -122.4164408 4160226.44 551520.71 101.62 42.81 -0.12 3.54

45 37.5876624 -122.4164308 4160226.96 551521.59 101.67 43.84 -0.15 3.59

46 37.58766559 -122.4164194 4160227.32 551522.6 101.77 44.89 0.03 3.69

47 37.5876695 -122.4164088 4160227.76 551523.53 101.8 45.92 0.1 3.72

48 37.58767423 -122.416399 4160228.29 551524.39 101.85 46.93 0.05 3.77

49 37.58767842 -122.4163897 4160228.76 551525.21 101.88 47.87 0.04 3.8

50 37.5876836 -122.41638 4160229.34 551526.06 101.92 48.9 -0.05 3.84

51 37.58768796 -122.4163694 4160229.83 551527 101.97 49.96 -0.02 3.89

52 37.58769252 -122.4163606 4160230.34 551527.77 101.98 50.88 -0.1 3.9

53 37.5876967 -122.4163506 4160230.81 551528.65 102.04 51.88 -0.08 3.96

54 37.58770098 -122.4163403 4160231.29 551529.56 102.11 52.91 -0.06 4.03

55 37.58770562 -122.4163305 4160231.81 551530.42 102.15 53.91 -0.09 4.07

56 37.58770999 -122.4163205 4160232.3 551531.3 102.2 54.92 -0.09 4.12

57 37.58771238 -122.4163124 4160232.57 551532.01 102.26 55.67 0.02 4.18

58 37.58771621 -122.4163023 4160233 551532.9 102.45 56.66 0.07 4.37

59 37.58771948 -122.4162903 4160233.37 551533.96 102.61 57.76 0.26 4.53

Appendix 5. Acquisition and Geometry for Profile 9 Sta # Latitude Longitude Northing Easting Altitude Local X Local Y Local Z

1 37.59001349 -122.4191961 4160486.29 551275.84 100.27 0 0.83 0

2 37.59000447 -122.4191405 4160485.32 551280.75 100.76 4.99 0.54 0.49

3 37.58999546 -122.4190859 4160484.35 551285.58 101.43 9.91 0.24 1.16

4 37.58998653 -122.4190296 4160483.39 551290.56 101.75 14.97 -0.03 1.48

5 37.58998085 -122.4189742 4160482.79 551295.45 102.24 19.9 0.05 1.97

6 37.5899739 -122.4189176 4160482.05 551300.45 102.94 24.95 0 2.67

7 37.58996633 -122.4188628 4160481.24 551305.3 103.28 29.87 -0.14 3.01

8 37.58995902 -122.4188066 4160480.46 551310.26 103.45 34.89 -0.23 3.18

9 37.5899512 -122.4187559 4160479.62 551314.74 103.33 39.44 -0.45 3.06

10 37.58994621 -122.4186946 4160479.1 551320.16 103.01 44.88 -0.23 2.74
53

11 37.58994089 -122.418639 4160478.54 551325.07 102.56 49.82 -0.11 2.29

12 37.58993466 -122.4185822 4160477.88 551330.09 102.29 54.89 -0.07 2.02

13 37.58992862 -122.4185265 4160477.24 551335.01 101.83 59.85 -0.03 1.56

14 37.58992258 -122.4184712 4160476.6 551339.9 101.45 64.78 0 1.18

15 37.58991428 -122.4183978 4160475.72 551346.38 100.49 71.32 0.02 0.22

16 37.5899095 -122.4183594 4160475.21 551349.78 100.29 74.76 -0.02 0.02

17 37.58990218 -122.4183013 4160474.43 551354.91 101.12 79.94 -0.09 0.85

18 37.58989497 -122.4182462 4160473.66 551359.78 101.03 84.87 -0.19 0.76

19 37.5898863 -122.4181872 4160472.73 551365 100.92 90.17 -0.4 0.65

20 37.58988152 -122.4181327 4160472.23 551369.81 101.08 95.01 -0.23 0.81

21 37.58987502 -122.4180759 4160471.54 551374.83 101.1 100.07 -0.23 0.83

22 37.58986754 -122.4180201 4160470.74 551379.76 101.17 105.07 -0.35 0.9

23 37.5898623 -122.4179638 4160470.19 551384.74 100.91 110.07 -0.21 0.64

24 37.58985752 -122.4179075 4160469.69 551389.71 101.06 115.07 -0.02 0.79

25 37.58985184 -122.4178524 4160469.09 551394.58 101.34 119.97 0.05 1.07

26 37.58984372 -122.4177966 4160468.22 551399.51 101.27 124.98 -0.14 1

27 37.58983938 -122.4177382 4160467.77 551404.67 101.68 130.15 0.12 1.41

28 37.58983217 -122.4176839 4160467 551409.47 102.6 135.01 0.02 2.33

29 37.58982603 -122.4176272 4160466.35 551414.48 101.61 140.06 0.06 1.34

30 37.58982017 -122.4175715 4160465.73 551419.4 102.35 145.02 0.12 2.08

31 37.58981403 -122.4175163 4160465.08 551424.28 102.95 149.94 0.14 2.68

32 37.58980799 -122.4174604 4160464.44 551429.22 103.59 154.92 0.19 3.32

33 37.58980205 -122.4174067 4160463.81 551433.96 104.26 159.7 0.21 3.99

34 37.58979609 -122.4173511 4160463.18 551438.87 104.98 164.65 0.26 4.71

35 37.58979014 -122.4172956 4160462.55 551443.78 105.7 169.6 0.31 5.43