Prepared in cooperation with California Geological Survey

2018 U.S. Geological Survey–California Geological Survey 

Fault-Imaging Surveys Across the Hollywood and Santa 

Monica Faults, Los Angeles County, California

By Rufus D. Catchings, Janis Hernandez, Mark R. Goldman, Joanne H. Chan, Robert R. Sickler, Brian Olson, and 

Coyn J. Criley

Open-File Report 2020–1049

U.S. Department of the Interior 

U.S. Geological Survey 
ii

U.S. Department of the Interior 

DAVID BERNHARDT, Secretary 

U.S. Geological Survey 

James F. Reilly II, Director 

U.S. Geological Survey, Reston, Virginia: 2020

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Suggested citation:

Catchings, R.D., Hernandez, J., Goldman, M.R., Chan, J.H., Sickler, R.R., Olson, B., and Criley,

C.J., 2020, 2018 U.S. Geological Survey–California Geological Survey fault-imaging surveys 

across the Hollywood and Santa Monica Faults, Los Angeles County, California: U.S. Geological 

Survey Open-File Report 2020–1049, 42 p., https://doi.org/10.3133/ofr20201049. 

Associated data for this publication: 

Goldman, M.R., Catchings, R.D., Chan, J.H., Sickler, R.R., Criley, C.C., Hernandez, J.L., and 

Olson, B., 2020, Data release for the 2018 U.S. Geological Survey–California Geological Survey 

fault-imaging surveys across the Hollywood and Santa Monica Faults, Los Angeles County, 

California: U.S. Geological Survey data release, https://doi.org/10.5066/P9ENA8D4. 

ISSN 2331-1258 (online) 
iii

Acknowledgments

Partial funding for this work was provided by the California Geological Survey (CGS). We thank 

CGS for identifying and securing the investigative fault sites. We thank Deshawn Brown, Michael 

DeFrisco, Erik Frost, Maxime Mareschal, Gordon Seitz, Brian Swanson, and Christopher Tran of 

the California Geological Survey for assistance in acquiring the data for this report. We thank the 

First Presbyterian Church of Hollywood, the City of Los Angeles, and the City of Beverly Hills for 

access. We thank Yong-Gang Li of the University of Southern California, and Walter Mooney of the 

U.S. Geological Survey (USGS), for reviewing the manuscript.

We thank the following USGS scientists: Kerri Gefeke, Dan Langermann, Belle Philibosian, and Ali 

Pickering; we also thank USGS volunteers Joseph Catchings, Shirley Imsand, Richard Philibosian, 

and Nathan Suits, for assistance in acquiring the data for this report. We thank Shane Detweiler, 

Mike Diggles, and Taryn Lindquist (all USGS) for editing and formatting and reviewing.
iv

Contents

Acknowledgments............................................................................................................................................................. iii

Abstract ..............................................................................................................................................................................1

Introduction.........................................................................................................................................................................1

Seismic Methodologies......................................................................................................................................................2

Guided-Wave Methodology ...........................................................................................................................................3

Tomography, MASW, and Reflection Methodologies...................................................................................................4

Hollywood Fault Data Acquisition and Profiles.................................................................................................................5

Hollywood Fault Profile HW1.........................................................................................................................................5

Hollywood Fault Profile HW2.........................................................................................................................................7

Guided-Waves Results for Profile HW1............................................................................................................................8

Guided-Wave Data Analysis for Profile HW1 ...............................................................................................................9

Tomography, MASW, and Reflection Results for Profile HW1........................................................................................9

Profile HW1 VP Model....................................................................................................................................................9

Profile HW1 VS Model..................................................................................................................................................12

Profile HW1 VP/VS Ratios, Tomography Model..........................................................................................................13

Profile HW1 Poisson’s Ratios, Tomography Model....................................................................................................14

Profile HW1 MASRW Model.........................................................................................................................................15

Profile HW1 MASLW Model .........................................................................................................................................16

Profile HW1 VP/VS (VP Tomography and VS MASRW) Model ...................................................................................17

Profile HW1 VP/VS (VP Tomography and VS MASLW) Model....................................................................................17

Profile HW1 P-Wave Reflection Stack ........................................................................................................................18

Profile HW1 S-Wave Reflection Stack ........................................................................................................................19

Summary of Seismic Indicators of Faulting along Profile HW1 .....................................................................................19

Guided-Wave Results for Profile HW2............................................................................................................................22

Data Analysis for Guided-Wave Survey HGW2 .........................................................................................................22

Data Analysis for Guided-Wave Survey HGW3 .........................................................................................................22

Tomography, MASW, and Reflection Results for Profile HW2......................................................................................23

Profile HW2 VP Model..................................................................................................................................................28

Profile HW2 VS Model (from MASRW) ........................................................................................................................28

Profile HW2 VP/VS Model (VP Tomography and VS MASRW)...................................................................................29

Profile HW2 Poisson’s Ratio Model (VP Tomography and VS MASRW) ...................................................................30

Summary of Seismic Indicators of Faulting along Profile HW2 .....................................................................................30

Summary of Observations, Hollywood Fault ..................................................................................................................31

Santa Monica Fault Data Acquisition (Beverly Hills)......................................................................................................32

Santa Monica Fault Data Analysis ..................................................................................................................................34

Guided-Wave Data Analysis for Profile BH1 ..............................................................................................................35
v 

Beverly Hills Profile BH2 Guided-Waves ....................................................................................................................35

Summary of Observations, Santa Monica Fault, Beverly Hills ......................................................................................37

References Cited .............................................................................................................................................................39

Figures

Figure 1. Mosaic of Google Earth images of the greater Los Angeles area, showing locations of the Hollywood 

Fault, Santa Monica Fault, and other faults. ................................................................................................2

Figure 2. Google Earth image of study area along Hollywood Fault ..........................................................................6

Figure 3. Google Earth image of Hollywood Fault study area near Profile HW1.......................................................7

Figure 4. Google Earth image of Hollywood Fault study area near Profile HW2.......................................................8

Figure 5. Stacked guided-wave shot gathers for Profile HW1..................................................................................10

Figure 6. Plot of peak ground velocity (PGV) of guided waves for each recording channel along Profile HW1; and 

plot of time of arrival of corresponding PGV values...................................................................................11

Figure 7. Tomographic P-wave velocity (VP) model along Profile HW1...................................................................12

Figure 8. Tomographic S-wave velocity (VS) model along Profile HW1...................................................................13

Figure 9. Tomographic VP/VS ratio model along Profile HW1 ..................................................................................14

Figure 10. Tomographic Poisson’s ratio model along Profile HW1. ...........................................................................15

Figure 11. S-wave velocity (VS) model inferred from Rayleigh waves. ......................................................................16

Figure 12. S-wave velocity (VS) model inferred from Love waves..............................................................................17

Figure 13. VP/VS ratio model along Profile HW1 derived from a combination of our VP tomography model and our 

MASRW VS model........................................................................................................................................18

Figure 14. Poisson’s ratio model along Profile HW1 derived from combination of our VP tomography model and 

our MASLW VS model..................................................................................................................................19

Figure 15. Low-resolution P-wave reflection stack for Profile HW1............................................................................20

Figure 16. Low-resolution S-wave reflection stack for Profile HW1............................................................................21

Figure 17. Stacked guided-wave shot gather for Profile HW2....................................................................................23

Figure 18. Plot of peak ground velocities (PGV) of guided waves for each recording channel along part of Profile 

HW2, and plot of travel times from SP1 to Profile HW2 ............................................................................24

Figure 19. Stacked guided-wave shot gathers for Profile HW2 ..................................................................................25

Figure 20. Plot of all peak ground velocities (PGV) of guided waves for each recording channel along part of 

Profile HW2, and travel times of PGV values; plot of PGV of guided waves along part of Profile HW2, 

and travel times of PGV values. .................................................................................................................27

Figure 21. In-line P-wave shot gather along Profile HW2, south of Yucca Street......................................................28

Figure 22. Tomographic P-wave velocity (VP) model along Profile HW2...................................................................29

Figure 23. S-wave velocity (VS) model along Profile HW2..........................................................................................30

Figure 24. VP/VS ratio model along Profile HW2, derived from combination of our VP tomography model and our 

MASRW VS model........................................................................................................................................31

Figure 25. Poisson’s ratio model along Profile HW1, derived from combination of our VP tomography model and 

our MASRW VS model saturated zone between two faults. Locations of nearby streets are shown. 

Abbreviation: m, meter(s)............................................................................................................................32
vi 

Figure 26. Google Earth image of Santa Monica Fault in our study area in Beverly Hills.........................................33

Figure 27. Stacked guided-wave shot gather for BHGW1 seismic survey................................................................. 34

Figure 28. Plot of peak ground velocity (PGV) of guided waves for each recording channel along BHGW1 survey. 

and plot of time of arrival of corresponding PGV values ...........................................................................36

Figure 29. Stacked guided-wave shot gather for Profile BH2 .....................................................................................37

Figure 30. Plot of peak ground velocity (PGV) of guided waves for recording channels along BHGW2 survey. and 

plot of time of arrival of corresponding PGV values...................................................................................38

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Flow rate

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

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

Abbreviations

1-D one dimensional

2-D two dimensional

AGC automatic gain control

AWD accelerated weight drop

CGS California Geological Survey

HGW1 Hollywood guided-wave survey 1

HGW2 Hollywood guided-wave survey 2

HGW3 Hollywood guided-wave survey 3

HRR1 Hollywood refraction-reflection survey 1

HRR2 Hollywood refraction-reflection survey 2

HW1 Hollywood seismic profile 1 (P-wave survey)

HW2 Hollywood seismic profile 2 (S-wave survey)

HW3 Hollywood seismic profile 3 (P-wave survey)

Hz hertz

MASW multichannel analysis of surface waves

MASLW MASW for Love waves

MASRW MASW for Rayleigh waves

PGV peak ground velocity

VP P-wave or compressional-wave velocity

VP/VS ratio ratio of P-wave velocity to S-wave velocity

VS S-wave or shear-wave velocity

USGS U.S. Geological Survey

UTC coordinated universal time
1 

2018 U.S. Geological Survey–California Geological Survey 

Fault-Imaging Surveys Across the Hollywood and Santa 

Monica Faults, Los Angeles County, California

By Rufus D. Catchings,1 Janis Hernandez,2 Mark R. Goldman,1 Joanne H. Chan,1 Robert R. Sickler,1 Brian Olson,2

and Coyn J. Criley1

Abstract

We acquired multiple types of seismic data across the Hollywood Fault in Hollywood, Calif.,

and the Santa Monica Fault in Beverly Hills, Calif., in May and June 2018. On the basis of our data, we 

infer near-surface locations of various traces of these faults. 

From two separate profiles across the Hollywood Fault, we evaluated multiple seismic datasets 

and models, including guided-wave data, tomographic VP data, tomographic VS data, VP/VS and 

Poisson’s ratio models derived from tomographic VP and VS data, Rayleigh-wave–based VS models, 

Love-wave–based VS models, VP/Vs and Poisson’s ratio models (derived from combinations of 

tomographic-based VP and surface-wave–based VS models), P-wave reflection images, and S-wave

reflection images. All of these data and models can be used to delineate near-surface faulting, and the 

data consistently infer near-surface fault traces of the Hollywood Fault in the same locations. 

Importantly, the combined data indicate more than one near-surface fault trace of the Hollywood Fault. 

Between North Bronson and North Gower Avenues, evidence exists for a near-surface trace of the 

Hollywood Fault slightly south of Carlos Avenue. Farther west, along Argyle Avenue, our data contain 

high levels of cultural noise, but we interpret near-surface faulting slightly south of the intersection of 

Carlos and Argyle Avenues and between Carlos Avenue and Yucca Street. 

For the Santa Monica Fault in Beverly Hills, we acquired guided-wave data only along Lasky 

Drive between Moreno Drive and South Santa Monica Boulevard, owing to limited access permissions.

However, we used two separate source locations to generate the guided-wave data (SP1 and SP2). The 

data from more distant source location (relative to the recording array, SP1) were noisy, but on the basis 

of those data, we infer near-surface faulting at several locations along Lasky Drive, with concentrated 

near-surface faulting slightly south of the intersection of Lasky Drive and Charleville Boulevard.

Guided-wave data generated at the closer source location (relative to recording array, SP2) more clearly 

show evidence for distributed near-surface faulting at several locations along Lasky Drive, with 

concentrated faulting near the intersection of Lasky Drive and Charleville Boulevard. 

Although the seismic surveys across both faults provide strong evidence for the locations of 

near-surface fault traces, the seismic data provide little or no information about the rupture history of the 

fault traces. 

Introduction

In May and June 2018, the U.S. Geological Survey (USGS) and the California Geological 

Survey (CGS) jointly conducted a series of seismic investigations in Los Angeles County, Calif., that 

1

U.S. Geological Survey

2

California Geological Survey
2 

were aimed at locating near-surface traces of the Hollywood Fault in Hollywood, Calif., and the Santa 

Monica Fault in Beverly Hills, Calif. (fig. 1). For the Hollywood Fault, we acquired four seismic 

surveys along two transects, from which we evaluated five types of seismic data, as well as multiple data 

combinations that can be used to evaluate near-surface faulting. We used active sources to generate body 

waves, surface waves, and guided waves, and from those data, we evaluated (1) P-wave velocities (VP), 

S-wave velocities (VS), and their ratios using tomography, (2) S-wave velocities (VS) using multichannel 

analysis of surface waves (MASW) on Rayleigh and Love waves, (3) peak ground velocities (PGV) of 

guided waves, (4) reflection images, and (5) combinations of those data. For the Santa Monica Fault, we 

acquired two guided-wave seismic surveys along Laskey Drive, from which we evaluated PGV of 

guided waves. In this report, we present images, models, and interpretations for the acquired data.

Seismic Methodologies

Faulting produces physical effects in the shallow subsurface that can be observed using multiple 

seismic-imaging methods. Although various types of seismic data can be affected differently by nearsurface faulting, those effects generally occur within the fault zone at the same locations. As a result, 

using multiple seismic datasets can provide greater confidence in the locations of near-surface faults. 

Figure 1. Mosaic of Google Earth images of the greater Los Angeles area, showing locations of the Hollywood 

Fault, Santa Monica Fault, and other faults. Small red rectangles indicate locations of Hollywood and Beverly Hills 

seismic profiles. Red lines show locations of historic faulting. Abbreviation: km, kilometer(s).
3 

Here, we briefly describe some of these effects and how they relate to the seismic methods used in this 

investigation.

Shearing during the faulting process reduces the rigidity of faulted rocks and materials. As a

result, both P- and S-wave velocities (VP and VS, respectively) decrease within fault zones relative to the 

surrounding rock mass. Empirical studies using laboratory data (Wang and others, 1978), active-source 

refraction data (Healy and Peake, 1975; Mooney and Luetgert, 1982; Mooney and Ginzburg, 1986; 

Jarchow and others, 1994; Catchings and others, 1998, 2002, 2008, 2009, 2014, 2016; Catchings, 1999), 

seismic-velocity logs (Boness and Zoback, 2004 ), earthquake-source data (Mayer-Rosa, 1973; Aki and 

Lee, 1976; Thurber, 1983; Eberhart-Phillips, 1990; Thurber and Atre, 1993; Thurber and others, 1995; 

Eberhart-Phillips and Michael, 1998), and guided-wave data (Leary and others, 1987; Li and Vidale, 

1996; Li and others, 2000, 2007; Korneev and others, 2003; Li and others, 2014; Catchings and others, 

2016) show a significant reduction (as much as 50%) in seismic velocities within fault zones. 

These reductions in VP and VS that are due to faulting typically are seen in velocity models as 

near-vertical zones of low seismic velocities. However, in the shallow subsurface, low-velocity fault 

zones can be obscured in VP models because of the presence of near-surface groundwater, which causes 

VP in fault zones to increase, rather than decrease. In the shallow subsurface, VS, which is strongly 

affected by the shear modulus, is typically more affected by faulting than VP, which is strongly affected 

by the bulk modulus and the presence of groundwater. As a result, the ratios of VP to VS can be 

unusually high in fault zones, and such high ratios typically are highly diagnostic of near-surface 

faulting (Catchings and others, 2014). 

Where present, stratigraphic layers can be vertically offset by near-surface faulting, particularly 

for reverse and normal faulting. Seismic-refraction tomography is a highly useful method for identifying 

such vertical offsets, particularly when different rock types are juxtaposed across faults. Seismicreflection imaging is another particularly useful seismic method for identifying such vertical offsets 

when subhorizontally layered strata is present in the shallow subsurface. However, small vertical offsets 

may not be seen in the near-surface at the resolutions of many seismic-reflection surveys, particularly 

when faulting produces little vertical offset. 

Guided waves (see below) can also be highly diagnostic of near-surface faulting when a fault 

trace can be identified in at least one location along its length. Collectively, these methods have been 

shown to be highly diagnostic of near-surface faulting.

Guided-Wave Methodology

With respect to seismic-wave propagation, low-velocity fault zones can be considered as wave 

guides that channel seismic energy. A number of studies have documented the wave-guide effect and the 

seismic energy that travels along and within the fault zones. This seismic energy is referred to as faultzone-guided waves or fault-zone-trapped waves (Cormier and Spudich, 1984; Li and Leary, 1990; Li 

and others, 1990, 1997, 2000; Hough and others, 1994; Huang and others, 1995; Ben-Zion, 1998; 

Jahnke and others, 2002; Rovelli and others, 2002; Ben-Zion and others, 2003; Malin and others, 2006; 

Li and others, 2014). Fault-zone-guided waves travel exclusively within low-velocity fault zones, and 

once the seismic energy enters the fault zone, high-amplitude seismic energy results from coherent 

multiple reflections at the boundaries between low-velocity fault zones and higher velocity wall rocks 

(Cormier and Spudich, 1984; Leary and others, 1987; Li and Leary, 1990; Li and Vidale, 1996).

Propagation of the seismic waves in fault zones is somewhat similar to optical-fiber light transmission. 

The amplitudes of fault-zone-guided waves are typically much larger, and the velocities are much lower, 

than body waves that travel outside of the fault zone (Cormier and Spudich, 1984; Spudich and Olson, 

2001; Fohrmann and others, 2004; Ellsworth and Malin, 2011). Numerical studies have shown that highamplitude guided waves are generated and propagate within fault zones only when the source is located 

within, or very close to, the fault zone (Li and Leary, 1990; Li and Vidale, 1996; Ben-Zion, 1998; Ingel 
4 

and others, 2002) or when the source underlies a fault zone that extends only to shallow depths 

(Fohrmann and others, 2004). Thus, for most crustal faults, guided waves propagate only along faults 

that are continuous between the seismic source and the observation point, as a discontinuous fault

prevents lateral propagation of guided waves beyond the endpoint of the fault (Li and Vidale, 1996; 

Jahnke and others, 2002). Thus, the presence, continuity, and connectivity of faults can be inferred from 

the presence or absence of guided waves along faults (Catchings and others, 2016). 

Guided waves have been identified in most studies on the basis of their relatively low-velocity, 

high-amplitude waveforms that have dispersive wavetrains, which are recorded on a series of 

seismographs deployed across or along a fault zone. The waveforms can be forward-modeled to estimate 

physical properties of the fault zone, including geometry, Q (attenuation), velocities, and temporal 

changes in velocity (Li and others, 2014, 2016). Furthermore, the locations of stations that record the 

high-amplitude waveforms and long time durations can be used to infer the overall maximum width of a 

fault zone, but this method is not ideal for locating individual fault traces within the overall fault zone. 

In our study, we use peak amplitude (peak ground velocity [PGV]) of fault-zone-guided waves 

(Catchings and others, 2013, 2016) to more precisely locate individual fault traces within the overall 

fault zone. Because fault zones can be kilometers in width and can consist of multiple traces, evaluation 

of PGV is more effective in locating individual traces. For our present study, we identify guided waves 

as high-amplitude seismic waves that arrive later than the body waves (either VP or VS) and are narrowly 

confined to a set of stations. Guided waves can be measured on either vertical- or horizontal-component 

sensors (Malin and others, 1996), but in our present study, we use only data from horizontal-component 

sensors. 

Tomography, MASW, and Reflection Methodologies

To develop seismic images, we also used seismic-refraction tomography, multichannel analysis 

of surface waves (MASW), and seismic-reflection processing techniques in this study. We developed Pand S-wave seismic-refraction tomography models using first-arrival travel times and the modeling code 

of Hole (1992). The nonlinear travel-time-tomography method by Hole (1992) uses a finite-difference 

algorithm to solve the eikonal equation in computing first-arrival travel times from the source to the 

receiver, and the model is updated in iterative steps using backprojection. Because P- and S-wave 

geophones and their respective shots were colocated approximately every 2 meters (m), we 

parameterized both our VP and VS models using 2-m horizontal (x) and vertical (z) intervals. For the 

tomographic inversions, we used 1-D starting models developed from shot-gather modeling that 

assumed similar but differing vertical variations in velocity. All starting models produced similar final 

velocity models, having velocities that generally differed by less than 5 percent at any given location in 

the final models. The geometrical setup of the seismic profile allowed us to use reciprocal shot and 

geophone (receiver) pairs to determine travel times. First arrivals were measured at nearly every 

geophone (∼89) for each shot point (89) along the profile, totaling nearly 7,900 first arrivals for the P 

waves and for S waves. Although most first arrivals could be measured on most shot gathers, for some 

less energetic shots, we used reciprocal travel times from the more energetic shots to ensure travel-time 

consistency. 

We developed Rayleigh- and Love-wave VS models using a version of the MASW method (Park 

and others, 1999) that was developed by Hayashi and Suzuki (2004) and Hayashi (2008) and is available 

in the Geometrics 2D SeisImager software package. For MASW analysis, the SeisImager algorithm 

constructs common midpoint correlations to develop 1-D dispersion curves and 1-D VS models for each 

shot point along the seismic profiles, and, by laterally combining those VS models, a 2-D VS model can 

be developed for each seismic profile. Although the MASW method can be applied to Rayleigh- and 

Love-wave (surface wave) data, the MASW method was originally applied to Rayleigh waves (Xia and 

others, 1999) and is generally referred to as the MASW method in the scientific literature. However, the 
5 

method is sometimes referred to as the MASRW method (Yong and other, 2013). The MASW method 

also has been applied to Love waves and has been referred to as the MALW method (Yuan, 2011; Xia 

and others, 2012; Catchings and others, 2017) or the MASLW method (Yong and others, 2013). In this 

report, we use the MASRW and MASLW descriptors to differentiate between the MASW method when 

applied to Rayleigh and Love waves, respectively.

In seismic-reflection data processing, we followed procedures similar to those outlined by 

Brouwer and Helbig (1998). Processing steps included geometry installation, independent trace editing, 

timing corrections, automatic gain control (AGC), band-pass filtering, surgical muting of refractions, 

surface waves and airwaves, velocity analysis (tomographic and 1-D velocities), elevation static 

corrections and normal moveout correction (using refraction-tomography velocities), stretch muting, 

common-depth point stacking, and poststack AGC and band-pass filtering. We attempted to stack both 

the P- and S-wave reflection data to look for variations in the resolution of the images. 

Hollywood Fault Data Acquisition and Profiles

We acquired seismic data along profiles in Hollywood between May 23, 2018, and June 1, 2018. 

Data were acquired in several stages, with the data being recorded along the following two transects: (1) 

Profile HW1, which consisted of a 178-m-long, north-south-trending, linear profile (within a parking 

lot) located north of Hollywood Boulevard and about 80 m east of North Gower Street (fig. 2), and (2) 

Profile HW2, a 370-m-long, north-south-trending, linear profile along North Argyle Avenue, between 

Hollywood Boulevard and Franklin Avenue (fig. 3).

Hollywood Fault Profile HW1

Profile HW1 originated on the north side of Hollywood Boulevard and ended in the courtyard of 

the First Presbyterian Church of Hollywood. We conducted several types of seismic investigations along 

Profile HW1. The first seismic investigation was a guided-wave survey (HGW1), whereby the recording 

array was perpendicularly offset from the seismic source, which was generated by a 227-kilogram (kg) 

(500-pound [lb]) accelerated weight drop (AWD). We used 157 individual “shots” at the same physical 

location (SP1), and the individual “shots” were stacked to form a single shot gather containing faultzone-guided waves. Generally, the seismic source must be within or near a fault trace to generate guided 

waves, and so, accordingly, we placed SP1 within a known trace of the Hollywood Fault that had been 

previously investigated by core-boring and cone-penetration-testing (CPT) transects (Ninyo and Moore, 

2015a, b). 

The second seismic survey (HRR1) along Profile HW1 used active P-wave seismic sources (227-

kg AWD shots and 3.6-kg hammer shots) that were in line with the recording array. Both seismic 

sources generated seismic energy when an AWD or hammer vertically struck a steel plate on the ground 

surface. The recording array consisted of 89 vertical-component sensors that were spaced 2 m apart. For 

the HRR1 seismic survey, we recorded P-wave refraction, P-wave reflection, and Rayleigh-wave data 

that were evaluated for evidence of faulting. In acquiring the P-wave data, we generated seismic shots at 

locations coincident with the 89 sensors. We used two stacked AWD shots at each of the southernmost 

70 shot points, and four stacked hammer shots for each of the northernmost 19 shots, which were largely 

within the church courtyard. 

The third seismic survey (HRR2) along Profile HW1 used active S-wave sources that were in 

line with the recording array. We generated the seismic sources by horizontally striking a 3.6-kg 

hammer against an aluminum block that was tethered to the ground surface. The recording array 

consisted of 89 horizontal-component sensors that were spaced 2 m apart. For the HRR2 survey, we 

recorded S-wave refraction, S-wave reflection, and Love-wave data that were evaluated for evidence of 

faulting. In acquiring the S-wave data, we generated seismic shots at 78 (of 89) shot-point locations that 
6 

Figure 2. Google Earth image of study area along Hollywood Fault (yellow lines). Green lines show inferred 

location of faults of undetermined age. Blue lines show locations of seismic profiles: HW1 is shorter, eastern profile; 

HW2 is longer, western profile. Red stars show locations of shot points used to generate guided waves: SP2, star 

along profile HW1; SP1, circled star. Abbreviation: m, meter(s).

were coincident with horizontal-component sensors. Most of the unused shot-point locations were 

within the courtyard of the First Presbyterian Church of Hollywood, where the ground was covered with 

cement. To avoid damaging the cement, we chose not to have sources at sensor numbers 66, 69, and 81 

to 89. We used four stacked hammer-block shots for each shot point. 

We used three types of recording systems along Profile HW1. For in-line, P- and Rayleigh-wave 

seismic imaging, we used Mark Products 4.5-hertz (Hz), vertical-component sensors (geophones) that 

were attached to a refraction cable. For in-line, S- and Love-wave seismic imaging, we used Mark 

Products 4.5-Hz, horizontal-component sensors that were attached to the same refraction cable. For both 

types of sensors, the refraction cable was attached to two 60-channel Geometrics RX60 Strataview 

seismographs. For both the P- and S-wave surveys, we used a sampling rate of 0.5 milliseconds (ms), 

and data were recorded for 2 seconds (s). For guided-wave recording along Profile HW1, at each 

recording site, we used two stand-alone, Reftek RT-125 (Texan) seismographs that were attached to 

Sercel 4.5-Hz, 3-component L-28 sensors, and we used a sampling rate of 0.5 ms and a recording length 

of 3 s. 
7 

Figure 3. Google Earth image of Hollywood Fault study area near Profile HW1, showing distance scale (in 

meters [m]) along Profile HW1 and locations of shot points SP1 and SP2 (red stars). SP1 is located at the nearsurface fault trace, as determined by a core-boring and cone-penetration-testing (CPT) transect; SP2 is located at 

the near-surface trace of Hollywood Fault, as indicated by peak ground velocity of guided waves.

Hollywood Fault Profile HW2

Profile HW2 extended along the east side of North Argyle Avenue from Hollywood Boulevard

to Franklin Avenue, crossing Yucca Street and Highway 101 near the north end of the profile (fig. 4). As 

with Profile HW1, we conducted several types of seismic investigations along Profile HW2 or parts of 

it. The first seismic survey along Profile HW2 was a guided-wave survey (HWG2), from which guidedwave data were acquired. The second seismic survey was an in-line P-wave survey (HRR3), from which 

reflection, refraction, and MASRW (multichannel analysis of surface waves, Rayleigh waves) data were 

acquired. The third seismic survey was an S-wave survey (HRR4), from which we attempted to acquire 

reflection, refraction, and MASLW (multichannel analysis of surface waves, Love waves) data; however, 

we recorded only 13 S-wave shots for the HRR4 survey because our S-wave seismic sources were too 

weak to overcome the traffic noise along North Argyle Avenue. As a result, we did not process data for 

the third (HRR4) survey.

For the HRR3 in-line seismic survey, we deployed 66 channels, using 3-m spacing between each 

channel and having a total profile length of 195 m. The actively recording profile extended only from 
8 

Figure 4. Google Earth image of Hollywood Fault study area near Profile HW2, showing distance scale (in 

meters [m]) along Profile HW2 (North Argyle Avenue) and location of SP2 (circled red star). Red arrows along North 

Argyle Avenue denote two zones of probable faulting, as indicated by seismic data. SP2 is located at the nearsurface trace of Hollywood Fault, as indicated by peak ground velocity of guided waves.

Hollywood Boulevard to Yucca Street (fig. 4). We used a 227-kg AWD to generate P- and Rayleighwave seismic energy along the profile, and a shot point was colocated with every active channel except 

three of them that had obstructions that prevented the use of the AWD. The P- (and Rayleigh-) wave 

data were recorded using two Geometrics RX-60 seismographs that were attached to refraction cables 

and Sercel 4.5-Hz, single-component (vertical) sensors. 

Guided-Waves Results for Profile HW1

The guided-wave seismic survey (HGW1) along Profile HW1 was conducted on the night of 

May 24, 2018. Although we deployed 89 sensors that were spaced at 2-m intervals, ten of the sensors

experienced instrumental failure. The seismic source for the HGW1 survey was located about 215 m 

east of the recording array and approximately 100 m west of North Bronson Avenue, between Carlos 

Avenue to the north and Hollywood Boulevard to the south (fig. 3). To record guided waves with less 

cultural noise, we generated seismic sources (157 AWD shots) in the evening hours of May 24, 2018, 

beginning at about 18:06:11 (local time) and continuing until 18:57:40. The resulting data contained 

clear arrivals and strong guided-wave energy.
9 

Guided-Wave Data Analysis for Profile HW1

Guided waves generated during the HGW1 survey were identifiable as high-amplitude arrivals 

following the shear-wave arrivals (figs. 5A, B). As a result, we evaluated PGV on the seismic traces only 

for the part of the seismic record at and following the S-wave first arrival. We correlated the PGV of the 

guided waves and the travel times to differentiate the guided waves from other possible strong arrivals 

(figs. 6A, B). The data show that the highest PGV values, which are expected at fault traces, arrived at 

the recording array at about 1,200 ms (1.2 s), and, because the source was approximately 215 m from the 

recording array, we determined that the guided waves traveled (on average) at about 180 m/s. The 

earliest shear waves arrived at the recording array at about 800 ms (0.8 s), suggesting an average VS of 

about 270 m/s. Thus, the guided waves traveled at about 67 percent of the velocity of the shear waves, 

consistent with velocities expected of guided waves.

Because guided waves travel exclusively within fault zones as high-amplitude arrivals, the 

physical location of near-surface fault traces can be inferred from guided waves (fig. 6A), with the 

highest amplitudes occurring at the near-surface trace. Our analysis of the PGV of guided waves along 

Profile HW1 shows a prominent peak between channels 48 and 66 (meters 94–110) of the recording 

array, with the highest peak concentrated at channel 54 (meter 106) of Profile HW1. Although the 

highest PGV value occurs at channel 54, relatively high values also occur between channels 50 and 60 

(meters 98–118), suggesting a wider fault zone at slightly greater depths. PGV values are appreciably 

lower to the north and south of the apparent fault zone (channels 48–66, meters 94–110), but an 

asymmetry is present in PGV values, whereby values to the south are higher than those to the north. We 

interpret this asymmetry to indicate either a near-surface southward dip of the fault zone or some 

additional deeper fault traces to the south of meter 106 of the seismic profile. 

Our inferred fault location is also consistent with disruptions in lithology identified in previous 

borehole measurements (Group Delta, 2015). However, Group Delta (2015) interpreted this change in 

lithology as arising from a shallow-depth paleochannel at that location. We suggest, however, that a 

paleochannel cannot account for the presence of guided waves, the observed travel-time delay of the 

guided waves, or the discrete high PGV values at meter 106. As discussed below, a paleochannel also 

cannot account for other seismic anomalies observed at that location. Thus, we suggest that the lithology 

change and the high PGV values result from near-surface faulting near meter 106 of Profile HW1 .

In addition to the high PGV values at the apparent near-surface fault zone (meter 106), a zone of 

relatively higher PGV values is present between channels 1 and 18 (fig. 6A). Although this zone has 

high PGV values that would be expected of a deeper fault zone, the timing of the high PGV values (fig. 

6B) suggests that they are not generated by guided waves. Instead, we suggest that this zone of high 

PGV values may be caused by seismic energy generated by the subway system (Metro Red Line), which 

is located beneath Hollywood Boulevard. With respect to guided waves, a subway system would be 

somewhat analogous to a fault zone, whereby high-amplitude seismic and sound waves that are 

generated within the subway bore by moving trains would be trapped and would propagate within the 

subway bore.

Tomography, MASW, and Reflection Results for Profile HW1

For the in-line active-source surveys along Profile HW1, we evaluated VP, VS, VP/VS ratios, and 

Poisson’s ratios, using VP derived from tomography and VS derived from several methods. We also 

evaluated VP and VS reflection images. 

Profile HW1 VP Model

Along Profile HW1, our tomography model (fig. 7) shows that VP ranges from about 300 m/s 

(at the surface) to 2,800 m/s (at ~50 m depth). In the shallow subsurface, a change in the depth of the 
10 

Figure 5. A, Stacked guided-wave shot gather for Profile HW1 (guided-wave survey HGW1). Source is located at 

SP1; recording array is located along Profile HW1. P waves (P), S waves (S), and guided waves (GW) are labeled 

on shot gather. Data were band-pass filtered between 2 and 16 Hz. B, Same shot gather as in A, but filtered 

between 15 and 120 Hz (note that only P-waves and partial S-waves are prominent at higher frequencies). 

Locations of nearby streets are shown. Other abbreviation: ms, millisecond(s).
11 

Figure 6. A, Plot of peak ground velocity (PGV) of guided waves for each recording channel along Profile HW1; 

highest PGV values (yellow shading) are concentrated between channels 48 and 56, and highest PGV value is at 

channel 54 (meter 106). B, Plot of time of arrival of corresponding PGV values shown in A; highest PGV values 

coincide with delayed phases that arrive at about 1,200 ms. As can be seen from shot gather (see fig. 5A), these 

delayed phases correlate with guided waves; zones of high PGV of guided waves are expected within near-surface 

fault zones. Locations of nearby streets are shown. Other abbreviations: m, meter(s); ms, millisecond(s); s, 

second(s).
12 

Figure 7. Tomographic P-wave velocity (VP) model along Profile HW1, showing locations of nearby streets. 

Near-surface location of Hollywood Fault at meter 106 (as inferred by guided waves) correlates with sharp change 

in depth of 400-m/s velocity contour. At about 20 m depth, slightly south of inferred surface trace of Hollywood 

Fault, there is a zone of high velocities, especially velocities higher than about 1,500 m/s, which is consistent with a 

fault that acts as a groundwater barrier. Other abbreviations: m, meter(s); s, second(s).

400-m/s velocity contour is observed near meter 106 of the seismic profile, suggesting a lateral change 

in material properties there. This shallow change in materials overlies a deeper, dome-shaped set of 

velocity contours, suggesting a continuous change in velocities from the near-surface to the base of our 

velocity model. For VP values in excess of 1,500 m/s, the apex of the dome is located at meter 90 at 

about 20-m depth. Overall, the dome-shaped structure dips to the south. We have observed such 

domelike velocity structures elsewhere where groundwater saturation, which typically has VP of 1,500 

m/s in sediments, abruptly changes across faults. Such structures typically result from ponding of 

groundwater against faults that act as ground-water barriers. However, ponding typically occurs on the 

topographically upslope side of faults, unless water flows parallel to the fault or over the top of a fault 

that does not reach the surface (Catchings and others 2014). We suggest that the approximate depth to 

the top of groundwater along Profile HW1 is indicated by the 1,500-m/s velocity contour. 

Profile HW1 VS Model

Our tomographic VS model (fig. 8) shows that shear-wave velocities (VS) along Profile HW1 

range from about 200 m/s (at the surface) to about 490 m/s (at about 25-m depth). At shallow depths, VS

is lowest (~200 m/s) near meters 80 and between meters 95 and 106, but an abrupt change in VS is 
13 

Figure 8. Tomographic S-wave velocity (VS) model along Profile HW1, showing locations of nearby streets. 

Near-surface location of Hollywood Fault at meter 106 (as inferred by guided waves and P-wave velocities) 

correlates with a sharp change to higher velocities to the north and a relatively low-velocity zone at depths greater 

than about 15 m. Such near-vertical, S-wave, low-velocity zones are consistent with faulting. Other abbreviations: 

m, meter(s); s, second(s); VE, vertical exaggeration.

observed at about meter 106, where higher velocities occur at shallower depths to the north. This abrupt 

change in VS continues vertically to the base of the velocity model at about 30 m depth. Zones of abrupt 

vertical changes in VS are consistent with faulting because faults cause decreases in VS owing to 

shearing. The general low-velocity zone associated with our interpreted fault dips about 79° to the south.

Profile HW1 VP/VS Ratios, Tomography Model

We developed a model of VP/VS ratios (fig. 9) along Profile HW1 by dividing VP by VS at each 

node of the velocity models. VP/VS ratios along Profile HW1 range from about 1 at the surface (in the 

south and extreme north) to about 4.4 at about 30-m depth (near meter 80). In a manner similar to the VP

structure along Profile HW1, we observe a domelike structure for all VP/VS values in the vicinity of 

meters 75 to 106, but the dome is most pronounced at depths greater than about 15 m. Overall, a slightly 

southward dip of the structure is observed. Water-saturated faults are expected to have high VP/VS ratios 

because the presence of water causes an increase in VP, and also because shearing causes a larger 

decrease in VS than VP, resulting in high values of VP/VS. Typical hard rocks have VP/VS ratios of about 

1.72, but sediments can have VP/VS ratios in excess of 3. Furthermore, Catchings and others (2014) 

showed that faulted sediments have higher VP/VS ratios beneath the groundwater table. Accordingly, we 
14 

Figure 9. Tomographic VP/VS ratio model along Profile HW1, showing locations of nearby streets. Near-surface 

location of Hollywood Fault at meter 106 (as inferred by guided waves and P- and S-wave velocities) correlates with 

a shallow-depth zone of high VP/VS ratios. Below the inferred (1,500 m/s) water table, VP/VS ratios are unusually 

high (as high as 4.6) in upper 30 m; water-saturated fault zones typically have high VP/VS ratios. Other 

abbreviations: m, meter(s); s, second(s); VE, vertical exaggeration.

interpret the relatively high VP/VS ratios on Profile HW1 to be the result of groundwater variations 

associated with faulting.

Profile HW1 Poisson’s Ratios, Tomography Model

We developed a model of Poisson’s ratio (fig. 10) along Profile HW1 using the following 

relationship between VP and VS: 

vv = 3Κ − 2μμ

6Κ + 2μμ (1) 

= ��Vp

Vs�

2

−2�

�2�Vp

Vs�

2

−2�, (2) 

where 

ν is Poisson’s ratio;

Κ is the bulk modulus;

μμ is the shear modulus;
15 

 VP is the P-wave velocity; and

 VS is the S-wave velocity. 

The value of ν ranges from about 0.05 to about 0.45 along profile HW1. The very low values of ν are 

associated with the shallowest velocity structure (unsaturated zone), and the highest values occur in the 

deepest materials (below the water table). In the shallow subsurface, ν is most strongly influenced by 

groundwater saturation, but lithology (such as clays) also can have a strong influence. A ν value of 0.5 is 

indicative of a fluid, and, in shallow sediments, a ν value above about 0.43 to 0.44 has been associated 

with the top of the groundwater table (Catchings and others 2007, 2014). Overall, the ν structure along 

Profile HW1 is similar to the VP/VS ratio structure, which are both indicative of a water-saturated fault at 

depth. 

Profile HW1 MASRW Model

Using Rayleigh waves that were recorded along Profile HW1, we used the MASW method to 

develop a second VS model (fig. 11) for Profile HW1. However, the MASW method is inherently a oneFigure 10. Tomographic Poisson’s ratio model along Profile HW1, showing locations of nearby streets. Nearsurface location of Hollywood Fault at meter 106 (as inferred by guided waves, P- and S-wave velocities, and VP/VS

ratios) correlates with a shallow-depth zone of high Poisson’s ratios. At depths of about 20 m, Poisson’s ratios are 

shown to be as high as 0.45 below and slightly southwest of the surface trace of Hollywood Fault. Fluids have a 

Poisson’s ratio of about 0.5, and Poisson’s ratios of about 0.43 have been shown to correlate with groundwater 

table (Catchings and others, 2008). Water-saturated fault zones typically have high Poisson’s ratios. Other 

abbreviations: m, meter(s); s, second(s); VE, vertical exaggeration.
16 

Figure 11. S-wave velocity (VS) model inferred from Rayleigh waves, using multichannel analysis of surface 

waves (MASW) method. Near the inferred near-surface Hollywood Fault, our MASRW VS model infers a zone of low 

VS in upper few meters, underlain by a zone of high VS at about 10 m and also a zone of low VS to at least 40 m 

depth. Such near-vertical low-velocity zones are consistent with near-vertical faulting. Although details of the VS

model determined from MASW are slightly different from those of the VS tomography model, both velocity 

anomalies are similar and are consistent with faulting near meter 106. Locations of nearby streets are shown. Other 

abbreviations: m, meter(s); s, second(s).

dimensional method, and, as a result, determination of VS can be affected by lateral variations in 

structure, velocity, and topography. Nevertheless, the MASW method can provide an indication of 

lateral variations in VS along Profile HW1. Our analysis of Rayleigh waves (MASRW) indicates that VS

along Profile HW1 ranges from about 200 m/s in the shallow subsurface (meters 95–105) to as much as 

875 m/s at about 40-m depth. The shallowest VS values are consistent between the tomography and the 

MASRW models, with minimum VS values of about 200 m/s near meters 94 to 106, but MASRWinferred VS values are higher at depths greater than about 20 m in the MASRW model. In addition, the 

overall velocity structure is less variable and more linear in the MASRW model than the tomography 

model. However, both models suggest the presence of a general near-vertical low-velocity zone near 

meter 106 that extends to the base of the models. At about meter 106, the MASRW model indicates a 

more pronounced near-vertical low-velocity zone, which is highly consistent with a zone of near-vertical 

faulting (Catchings and others, 2014). Aligning the low-velocity contours in the MASRW model 

suggests that the shallow Hollywood Fault dips about 82° to the south. 

Profile HW1 MASLW Model

Using Love waves recorded along Profile HW1, we developed a VS model (fig. 12) using the 

MASW method. Our MASLW modeling indicates that VS ranges from about 250 m/s at shallow depths 

to about 675 at about 50-m depth. Although the overall MASLW model varies from both the MASRW 

model and the tomography model, VS and the overall VS structure have similarities to those of both the 

tomography and MASRW models. In particular, the near-vertical low-velocity zone in the vicinity of 

meters 102 to 120 is seen in all the models and is consistent with a fault in that area. However, whereas 

the MASRW and tomography models and the asymmetry of the PGV of guided waves suggest a slight 
17 

Figure 12. S-wave velocity (VS) model inferred from Love waves, using multichannel analysis of surface waves 

(MASW) method. Near the inferred near-surface Hollywood Fault, our MASLW VS model infers zones of low VS in 

upper few meters and also below about 20 m depth. Such near-vertical low-velocity zones are consistent with nearvertical faulting. Although details of VS models determined from MASRW, MASLW, and tomography differ in 

absolute velocity, velocity anomalies determined from all three methods are similar and are consistent with faulting.

Locations of nearby streets are shown. Other abbreviations: m, meter(s); s, second(s).

southward fault dip at shallow depths, the MASLW model indicates a slight northward (79°) fault dip at 

shallow depths, on the basis of the observed low-velocity contours.

Profile HW1 VP/VS (VP Tomography and VS MASRW) Model

Using VP from our tomography model (fig. 7) and the VS from our MASRW model (fig. 11), we 

developed a hybrid VP/VS–ratio model (fig. 13) along Profile HW1. Our tomographic/MASRW hybrid 

VP/VS–ratio model suggests that VP/VS ratios range from about 1.2 at the surface to 3.8 at 40-m depth. 

This range of values in hybrid VP/VS ratios is slightly lower than the maximum VP/VS ratio value (4.4) 

indicated by the tomographic VP/VS–ratio model (fig. 9); however, the hybrid VP/VS–ratio model 

indicates a pronounced high VP/VS–ratio (up to 3.8) zone centered at about meters 100 to 105, similar to 

the high value (4.4) in the tomographic VP/VS–ratio model. Because water-saturated fault zones are 

expected to cause concentrated high VP/VS–ratio zones, we suggest that the relatively wide zone of high 

VP/VS ratios at depth in the hybrid model is likely indicative of a wider fault zone in the upper 40 m 

depth of the velocity model. The hybrid VP/VS–ratio image indicates an overall near-vertical fault that is 

centered near meter 100; however, this image is also consistent with the presence of adjacent splay 

faults.

Profile HW1 VP/VS (VP Tomography and VS MASLW) Model

Using VP from our tomography model (fig. 7) and the VS from our MASLW model (fig. 12), we 

developed a second hybrid VP/VS–ratio model (fig. 14) along Profile HW1. Our tomographic/MASLW 

hybrid VP/VS–ratio model suggests that VP/VS ratios range from about 1.5 at the surface to 6.0 at 40- to 

50-m depth, with pronounced high values being observed beneath the central part of the profile. In the 
18 

Figure 13. VP/VS ratio model along Profile HW1 derived from a combination of our VP tomography model and our 

MASRW VS model. A zone of locally high VP/VS ratios occurs near the near-surface trace of Hollywood Fault 

(dashed lines), as inferred by multiple models in this study. Near-vertical zone of high VP/VS ratios is concentrated 

beneath the near-surface fault trace, as has been seen for other fault zones. Locations of nearby streets are shown. 

Other abbreviation: m, meter(s).

upper 30 m, all three VP/VS–ratio models infer similar structures, but the hybrid VP/VS–ratio models 

suggest a wider fault zone at depth and infer possible northward and southward dips. 

Profile HW1 P-Wave Reflection Stack

Using P-wave shot gathers from Profile HW1, we developed a low-resolution P-wave seismic 

reflection image (stack) of the shallow subsurface (fig. 15). The P-wave reflection stack indicates the 

presence of predominantly subhorizontal layering in the upper 20 m, with apparent slight folding 

centered near meter 100 of the profile. This unmigrated image suggests the presence of strong 

diffractions below about 20-m depth, centered near meter 100. Diffractions are caused by sharp 

boundaries in the subsurface, and faulting, which vertically offsets layers, is a typical cause of such 

diffractions, particularly when the diffractions are subvertically aligned, as seen in figure 15. Thus, the 

P-wave reflection image is consistent with a near-vertical fault located near meter 100. By aligning the 

diffractions over depths that range from about 20 to about 120 m, the alignment of diffractions suggests 

that the fault dips about 87° northward below 20-m depth (fig. 15). In addition, significant noise or 

surface waves is seen in the southern part of the reflection image, making it difficult to resolve the 
19 

Figure 14. Poisson’s ratio model along Profile HW1 derived from combination of our VP tomography model and 

our MASLW VS model. A zone of locally high Poisson’s ratios occurs near the near-surface trace of Hollywood Fault 

(white lines), as inferred by multiple models in this study. Near-vertical zone of high Poisson’s ratios is concentrated 

near the near-surface trace of Hollywood Fault, as has been seen for other fault zones. Locations of nearby streets 

are shown. Other abbreviation: m, meter(s).

structure along the south half of Profile HW1. The strong energy likely arises from either the Los 

Angeles Metro Rail (subway) Redline trains or car traffic along Hollywood Boulevard. 

Profile HW1 S-Wave Reflection Stack

Using S-wave shot gathers from Profile HW1, we developed a low-resolution S-wave seismic 

reflection image (stack) of the shallow subsurface (fig. 16). The S-wave reflection stack also indicates 

the presence of predominantly subhorizontal layering and an apparent fold centered near meter 100. 

Aligning the apex of the apparent fold—from about 20 to about 125 m—suggests that the deeper fault 

dips about 87 degrees northward, with the possibility of a splay fault dipping about 79° southward near 

the surface. High noise levels on the south end of the profile interferes with the seismic signal, making it 

difficult to delineate any possible fault structures.

Summary of Seismic Indicators of Faulting along Profile HW1

We evaluated 13 different seismic images along Profile HW1, including (1) PGV of guided 

waves, (2) tomographic VP, (3) tomographic VS, (4) tomographic VP/VS ratios, (5) tomographic Poisson’s 

ratios, (6) MASRW VS, (7) MASLW VS, (8) hybrid tomography/MASRW VP/VS ratios, (9) hybrid 
20 

Figure 15. Low-resolution P-wave reflection stack for Profile HW1. Strong diffractions are apparent beneath the 

inferred location of Hollywood Fault (red lines), beginning at about 10 m depth and extending to base of reflection 

image. Such diffractions are typically seen on unmigrated reflection images of faulted strata. Locations of nearby 

streets are shown. Abbreviation: m, meter(s).
21 

Figure 16. Low-resolution S-wave reflection stack for Profile HW1. Folds and diffractions are apparent beneath the 

inferred location of Hollywood Fault (red lines), beginning at about 10 m depth and extending to base of reflection 

image. Such disrupted layering is typically seen on reflection images of faulted strata. Locations of nearby streets 

are shown. Abbreviation: m, meter(s).

tomography/MASRW Poisson’s ratios, (10) hybrid tomography/MASLW VP/VS ratios, (11) hybrid 

tomography/MASLW Poisson’s ratios, (12) P-wave reflection, and (13) S-wave reflection. All 13 images 

presented here are consistent with a near-vertical fault located near meters 100 to 106 of Profile HW1. 

We suggest that the guided-wave results are likely most diagnostic of the location of faulting nearest the 

surface.
22 

Guided-Wave Results for Profile HW2

We evaluated two guided-wave seismic datasets recorded along Profile HW2, and both were 

recorded on the night of May 24, 2018, using the same recording system as was used along Profile 

HW1. However, the recording array for Profile HW2 was located along North Argyle Avenue, where 

significant traffic noise occurs. A total of 123 recording stations were surveyed along Profile HW2, but 

seismographs were not deployed at 11 stations owing to the presence of obstacles such as driveways and 

buried pipes. Of the stations deployed, six seismographs did not record data. 

The first guided-wave survey (HGW2) along Profile HW2 used the same source location (SP1) 

as was used for the HGW1 guided-wave survey along Profile HW1 (fig. 2). A total of 157 AWD shots 

were stacked to generate the guided waves for the HGW2 guided-wave survey. The perpendicular 

distance from SP1 to Profile HW2 was approximately 560 m, with longer distances to the north and to 

the south of the profile. The seismic sources (shots) for the HGW2 survey began on May 24, 2018, at 

20:24:43 (local time) and continued until 20:43:33.

The second guided-wave survey (HGW3) recorded along Profile HW2 used the same recording 

array as was used in the HGW2 survey; however, the seismic source (SP2) was located near the center 

of the Profile HW1 recording array (fig. 3), such that SP2 was located at the fault location inferred from 

an earlier borehole survey. The perpendicular distance from SP2 to Profile HW2 (Argyle Avenue) was 

approximately 350 m. We used a total of 151 AWD shots (stacked) to generate guided waves for the 

HGW3 seismic survey. The HGW3 survey shots began on May 24, 2018, at 21:29:37 (local time) and 

continued until 21:47:09. Ten of the seismographs used during the HGW3 survey did not record data.

Data Analysis for Guided-Wave Survey HGW2

Guided waves from the HGW2 survey were not easily identified because of high cultural-noise 

levels along Profile HW2 (North Argyle Avenue). In addition, heavy traffic along the overpass 

(Highway 101) over North Argyle Avenue, as well as heavy traffic on Hollywood Boulevard and 

subway trains, appear to be the major sources of noise that significantly reduced the signal-to-noise ratio 

of the HGW2 data. However, with approximately 157 stacked shots, the S-wave and later arrivals can be 

identified from data derived from the southern part of the HGW2 survey (fig. 17). From those data, we 

measured the PGV of the data from about 0.8 to about 2.0 s. The highest PGV values appear to be 

concentrated near Carlos Avenue and south of Yucca Street (figs. 18A, B) for the HGW2 survey. 

Although we urge extreme caution in evaluating the PGV of guided waves from such noisy data, the 

data suggest that guided waves may have been recorded south of Carlos Avenue and south of Yucca 

Street. The relatively high PGV values near Carlos Avenue and Yucca Street occur at times consistent 

with those expected for guided waves, traveling at about 50 percent of the apparent VS. 

We also evaluated data north of Yucca Street, but the noise levels from the Highway 101 

overpass were so high that we did not include those data in this report. We also observed relatively high 

PGV values between Yucca Street and Highway 101, but owing to the high cultural-noise levels, we 

have little confidence that the high PGV values are derived from guided waves. Thus, we suggest that 

the guided waves recorded on the HGW2 survey are indeterminate with respect to faulting and that 

performing a survey later at night, when cultural and highway noises are less prevalent, might have been 

more determinate.

Data Analysis for Guided-Wave Survey HGW3 

We acquired the HGW3 survey with the source at SP2 (First Presbyterian Church of Hollywood 

parking lot) and the recording array located along Profile HW2 (North Argyle Avenue). Data from the 

HGW3 survey also are very noisy (fig. 18) owing to the same noise sources described above for the 

HGW2 survey. It appears that those noise sources were even greater than was observed during the 
23 

Figure 17. Stacked guided-wave shot gather for Profile HW2 (guided-wave survey HGW2). Source is located at 

SP1; recording array is located along Profile HW2. Source and recording array are separated by about 560 m. High 

levels of cultural noise, which are prevalent before the P-wave arrival, are shown on shot gather, especially 

between channels 1 and 30 and near channel 105. Such high levels of cultural noise make it difficult to evaluate 

guided waves. P waves (P), S waves (S), and guided waves (GW) are inferred on shot gather. Data were bandpass filtered between 1.5 and 12 Hz. Locations of nearby streets are shown. Other abbreviation: ms, millisecond(s).

HGW1 survey, possibly because there was less traffic during the 21:00 hour time frame, which may 

have allowed for faster moving vehicles and greater overall noise. 

With 151 shots stacked, the main S-wave and apparent guided waves were difficult to identify on 

the shot gather (fig. 19). However, from the stacked data, we measured PGV values for the part of the 

survey that was south of Yucca Street (figs. 20A, B, C, D). We observe high PGV values in nearly the 

same location as seen from the HGW2 seismic survey, particularly south of Carlos Avenue and south of 

Yucca Street. However, we also observe high PGV values slightly north of Hollywood Boulevard, 

which are likely attributable to noises from the subway and from traffic on Hollywood Boulevard 

because the travel times are inconsistent with those expected for guided waves. In contrast, the high 

PGV values south of Carlos Avenue and south of Yucca Street occur at the approximate time expected 

for guided waves when the source is located at SP2. 

Tomography, MASW, and Reflection Results for Profile HW2 

We acquired an in-line, active-source P-wave seismic survey (HRR3) along Profile HW,2 using 

P-wave shots and vertical-component sensors that were attached (via refraction cables) to two 

Geometrics RX-60, multichannel seismographs. Unlike the guided-wave surveys (HGW2 and HGW3), 

we did not deploy sensors north of Yucca Street owing to the difficulty in deploying cables across 

Yucca Street; thus, the HRR3 survey was only about 200 m long. We used 66 vertical-component 

sensors and 63 AWD shot points for the HRR3 seismic survey. The AWD shots and sensors were 

colocated (1.5 m lateral offset) and spaced at 3-m intervals. The data were recorded for 2 s at a sampling 
24 

Figure 18. A, Plot of peak ground velocities (PGV) of guided waves for each recording channel along part of 

Profile HW2 (guided-wave survey HGW2), showing locations of nearby cross streets. Owing to high levels of 

cultural noise from Highway 101 north of Yucca Street, PGV values for channels north of Yucca Street were deleted 

from plot. Yellow shading highlights channels that have high levels of cultural noise south of Carlos Avenue (see fig. 

17). B, Plot of travel times from SP1 to Profile HW2. Travel times on north end of Profile HW2 were shifted to allow 

analysis within a limited time window, as higher propagation velocities on north end of profile resulted in shorter 

travel times. High PGV values on PGV plot correlate with delayed travel times on travel-time plot. Although 

contaminated with noise, high PGV values (red dots) may infer possible fault locations along profile HW2. Other 

abbreviations: m, meter(s); ms, millisecond(s); s, second(s).
25 

Figure 19. Stacked guided-wave shot gathers for Profile HW2 (guided-wave survey HGW3), showing (A) without 

time shifts to account for differences in propagation velocities and (B) with time shifts to account for differences in 

propagation velocities. Source was located at SP2: recording array was located along Profile HW2. There is about 

350 m between the source and the recording array. High levels of cultural noise, which are prevalent before P-wave 

arrival, are shown on shot gather, especially between channels 1 and 30 and near channel 105. Such high levels of 

cultural noise make it difficult to evaluate guided waves. P waves (P), S waves (S), and guided waves (GW) are 

inferred on shot gather. Data were band-pass filtered between 1.5 and 12 Hz. Locations of cross streets are shown.

Other abbreviation: ms, millisecond(s).
26 

Figure 20. A, Plot of all peak ground velocities (PGV) of guided waves for each recording channel along part of 

Profile HW2 (guided-wave survey HGW3), showing locations of nearby cross streets. B, Travel times of PGV values 

shown in A. Extremely high PGV values centered near Highway 101 have travel times and velocities that are 

inconsistent with those expected for guided waves; thus, we suggest that very high PGV values observed for 

stations near Highway 101 result from freeway noise and not from guided waves; most other PGV values along 

Profile HW2 are much lower. Slightly higher values are seen on channels 1 to 30, and those higher values may
27 

Figure 20 (cont.) result from cultural noises (cars or subway); however, travel times for slightly higher PGV 

values are generally in time frame expected for guided waves. C, Plot of PGV of guided waves along part of Profile 

HW2 (guided-wave survey HGW3) south of Yucca Street. High cultural noise is prevalent for channels 1 to 30, 

making it difficult to determine whether higher PGV values in that range result from guided waves. D, Travel times 

of PGV values shown in C. Relatively high PGV values (red dots) slightly south of Carlos Avenue and south of 

Yucca Street have travel times and propagation velocities that are consistent with expectations of guided waves; 

thus, we suggest possible faulting at those locations (see dashed green lines). Other abbreviations: m, meter(s); 

ms, millisecond(s); s, second(s).
28 

rate of 0.5 ms. Cultural-noise levels were high along North Argyle Avenue at the time of data 

acquisition, and the resulting shot gathers were noisy (fig. 21). As a result, we evaluated VS data that 

were derived from the surface-wave (Rayleigh wave) data using the MASW technique (fig. 22).

Combining the tomographic VP and the MASW VS data, we evaluated VP/VS ratios and Poisson’s ratios 

along Profile HW2 (figs. 23, 24, respectively). 

Profile HW2 VP Model

We used the data from the HRR3 survey to develop a VP model (fig. 22) for Profile HW2. The VP

values range from 400 m/s near the surface in the south to about 3,300 m/s at about 70 m depth near the 

center of the profile. An abrupt change in shallow velocities (~400 m/s) is observed at Carlos Avenue, 

with higher velocities to the north at shallow depths and progressively thicker lower velocity materials 

southward toward Hollywood Boulevard. The abrupt change in shallow VP at Carlos Avenue is similar 

to the change in VP seen along Profile HW1 at the apparent Hollywood Fault (fig. 7). The abrupt change 

in VP along both Profiles HW1 and HW2 occurs coincident with the zone of apparent high PGV values 

seen from guided waves. A similar change in VP also is observed just south of Yucca Street, where PGV 

of guided waves is locally high. Thus, both guided waves and VP are suggestive of near-surface faulting 

slightly south (10–25 m) of the center of Carlos Avenue and about 20 to 35 m south of the center of 

Yucca Street. 

Profile HW2 VS Model (from MASRW) 

From Rayleigh waves generated during the HRR3 seismic survey, we a developed MASW-based 

VS model (fig. 23) for Profile HW2. Our VS model shows that VS ranges from 200 m/s near the surface 

Figure 21. In-line P-wave shot gather along Profile HW2, south of Yucca Street. High cultural noise levels are 

particularly noticeable for channels 1 to 15. Multiples, owing to bouncing of seismic source (AWD), are prominent at 

travel times greater than 200 ms. Zone of asymmetric surface waves and refracted arrivals is present north and 

south of shot point, demonstrating large differences in structure to south versus to north. Locations of nearby 

streets are shown. Other abbreviations: m, meter(s); ms, millisecond(s); s, second(s).
29 

Figure 22. Tomographic P-wave velocity (VP) model along Profile HW2, showing locations of cross streets. 

Prominent VP anomalies are present along seismic profile, such as abrupt shallowing of 400-m/s velocity contour 

near Carlos Avenue. Similar change in velocity is observed at near-surface trace of Hollywood Fault along Profile 

HW1. This is also same location that relatively high PGV values are observed on guided-wave PGV plots (see fig. 

20). We interpret second change in shallow-depth VP south of Yucca Street, also consistent with guided-wave PGV 

values, to infer faulting. Other abbreviations: m, meter(s); s, second(s).

on the southern profile to about 675 m/s at about 30-m depth south of Carlos Avenue. From the south 

end of Profile HW2 (at Hollywood Boulevard) to approximately Carlos Avenue, a 7- to 10-m-thick zone 

of low-VS (<300 m/s) materials is present in the near surface; this layer pinches out at Carlos Avenue in 

a manner similar to that seen in the tomographic VP model (fig. 7). Between that 7- to 10-m-thick layer 

and the base of the model, VS is high relative to the north end of Profile HW2. A major lateral transition 

in VS is observed at all depths of the model, suggesting that a major change in structure is present, likely 

caused by faulting. Our VS model also shows that a pronounced, southward-dipping, low-velocity zone 

is present south of Yucca Street, as was also inferred on the VP model. This southward-dipping velocity 

structure may infer a southward-dipping fault south of Yucca Street. Both the VP and VS models suggest 

that an isolated zone of relatively high velocities is present near the surface between meters 130 and 160.

Profile HW2 VP/VS Model (VP Tomography and VS MASRW)

Using VP from the tomography model (fig. 22) and VS from the MASW-based model (fig. 23), 

we developed a VP/VS–ratio model (fig. 24) for Profile HW2. Our model suggests that VP/VS ratios range 

from about 1.5 near the surface south of Carlos Avenue to about 4.8 below 10 m depth between Carlos 
30 

Figure 23. S-wave velocity (VS) model along Profile HW2, inferred from Rayleigh waves using the multichannel 

analysis of surface waves (MASW) method. VS model shows abrupt increase in VS north of Carlos Avenue, with 

shallow structure similar to that modeled for VP model. Higher velocities (>400 m/s) are abruptly terminated near 

Carlos Avenue, suggesting slightly northwestward dip of probable fault. Change in VS also is observed south of 

Yucca Street, with prominent near-vertical low-velocity zone, inferring possible southwestward dip of fault there.

Locations of nearby streets are shown. Other abbreviations: m, meter(s); s, second(s).

Avenue and Yucca Street. The zone of highest VP/VS ratios is relatively wide near the top and decreases 

in width with depth, which suggests that two opposing faults join at depth. Thus, on the basis of our VP, 

VS, and VP/VS models, we suggest a northward-dipping fault near Carlos Avenue and a southwarddipping fault south of Yucca Street. 

Profile HW2 Poisson’s Ratio Model (VP Tomography and VS MASRW)

Using the same VP and VS models as used to develop our VP/VS–ratio model, we developed a 

Poisson’s ratio model for Profile HW2 (fig. 25). The Poisson’s ratio model infers a similar structure as 

that of the VP/VS–ratio model. Generally, subsurface materials in the upper about 20 m along Profile 

HW2 differ markedly from south to north, with the major change occurring at Carlos Avenue. This 

lateral variation in Poisson’s ratio values suggests a significant change in shallow-crustal properties that 

are likely related to groundwater saturation. Because faults usually act as groundwater barriers, this 

pronounced lateral change in Poisson’s ratio is consistent with the presence of a fault near Carlos 

Avenue. The highest Poisson’s ratio values along our model are confined to a zone between Carlos 

Avenue and Yucca Street, which would be consistent with bounding faults near Carlos Avenue and 

slightly south of Yucca Street. 

Summary of Seismic Indicators of Faulting along Profile HW2

We evaluated five seismic models along Profile HW2, including (1) PGV of guided waves from 

two source locations, (2) tomographic VP, (3) MASW VS, (4) hybrid tomography/MASRW VP/VS ratios, 

and (5) hybrid tomography/MASRW Poisson’s ratios. All of these models show prominent changes in 

shallow-depth structure near Carlos Avenue and slightly south of Yucca Street that are consistent with 

shallow faulting in those locations. We interpret these images as indicating a shallow-depth, northwarddipping fault near Carlos Avenue and a shallow-depth, southward-dipping fault south of Yucca Street, 

with both faults merging in the shallow subsurface.
31 

Figure 24. VP/VS ratio model along Profile HW2, derived from combination of our VP tomography model and our 

MASRW VS model. Shallow-depth, abrupt changes in VP/VS ratios are present in vicinity of Carlos Avenue and 

south of Yucca Street. Prominent VP/VS-ratio high is present at slightly greater depths between two abrupt changes 

in VP/VS ratios. This structure can be interpreted as showing two opposing fault traces. Locations of nearby streets 

are shown. Abbreviation: m, meter(s).

Summary of Observations, Hollywood Fault

We evaluated 13 seismic models and data combinations along Profile HW1 at the First 

Presbyterian Church of Hollywood parking lot (fig. 3). All of those data are consistent with near-surface 

faulting near meter 106 of Profile HW1, slightly south of Carlos Avenue. On the basis of the combined 

seismic data, we interpret the fault to slightly splay near the surface, having both northward and 

southward dips at shallow depths but a northward dip at depth. On the basis of the location of the fault 

identified in core borings and CPT transects at the Hollywood Courthouse building and our observed 

location along Profile HW1, we suggest that the fault strikes about N. 87o E. and has variable dips in the 

shallow subsurface. However, on the basis of the unmigrated reflection images, we suggest that the fault 

dips slightly northward at depth.

We evaluated five seismic models and data combinations along Profile HW2 along North Argyle 

Avenue in Hollywood. All of those data are consistent with, but not definitive of, near-surface faulting 

slightly south of Carlos Avenue and south of Yucca Street. Furthermore, additional fault traces may be 
32 

Figure 25. Poisson’s ratio model along Profile HW1, derived from combination of our VP tomography model and 

our MASRW VS model. Shallow-depth, abrupt changes in Poisson’s ratios are observed in vicinity of Carlos Avenue 

and south of Yucca Street. Prominent Poisson’s-ratio high is present at slightly greater depths between two abrupt 

changes in near-surface Poisson’s ratios, which we interpret as a highly saturated zone between two faults. 

Locations of nearby streets are shown. Abbreviation: m, meter(s).

present along Profile HW2, but the high levels of cultural noise in our data make it difficult to infer 

faulting elsewhere along North Argyle Avenue. On the basis of the fault locations along Profiles HW1 

and HW2 inferred from our data, we suggest that this strand of the Hollywood Fault strikes almost due 

east-west between the core boring/CPT transect at the Hollywood Courthouse and our seismic profile 

along North Argyle Avenue. Although traces of the fault may have variable dips in the shallow 

subsurface, we suggest that the overall dip is near vertical, with a slightly northward dip at depth.

Santa Monica Fault Data Acquisition (Beverly Hills)

On May 26, 2018, and on June 6, 2018, we conducted guided-wave seismic surveys across the 

suspected near-surface trace of the Santa Monica Fault in Beverly Hills, Calif. The recording array for 

both seismic surveys was located on the east side of Lasky Drive, between Moreno Drive and Santa 

Monica Boulevard (fig. 26). We refer to this profile as Profile BH1, and we refer to the two individual 

surveys as BHGW1 and BHGW2.

Survey BHGW1 was about 300 m long and consisted of approximately 149 recording sites, but 

six of the sites were not used because they would have blocked driveways. The data from survey 

BHGW1 were recorded on 4.5-Hz horizontal-component sensors, spaced at 2-m intervals, but data were 

not recorded at 20 sites owing to instrumental failures. The sampling rate was 2 ms. The seismic source 
33 

Figure 26. Google Earth image of Santa Monica Fault in our study area in Beverly Hills, showing locations of 

seismic surveys (BHGW1, BHGW2) recorded along Profile BH1 (cyan line). Scale (in meters [m]) is included along 

Profile BH1. Seismic sources were generated at SP1 and SP2 (red stars) at the near-surface trace of Santa Monica 

Fault, as inferred from geologic mapping. Recording arrays for BHGW1 and BHGW2 surveys were located in same 

place, except that BHGW2 survey extended farther north by about 50 m. Red arrows show zones where high PGV 

values (that have travel times consistent with guided waves) were recorded.

(227-kg AWD) used to generate guided waves was located approximately 30 m southwest of Century 

Park East and about 100 m southeast of Santa Monica Blvd, within an alley northwest of a parking 

garage. The first AWD shot started on May 26, 2018, at 21:42:05 (local time; 04:42:05 UTC), and the 

last shot was completed at 22:24:46 (local time; 05:24:46 UTC) on the same day. We stacked a total of 

198 individual shots to form a guided-wave shot gather. 

We decided to acquire a second seismic guided-wave survey (BHGW2) along Laskey Drive on 

June 6, 2018, when we discovered that the expected fault crossing was at the approximate north end of 

the BHGW1 survey, near the intersection of Lasky Drive and Charleville Boulevard. The recording 

stations for the BHGW2 survey were in the same locations as that of the BHGW1 survey, but the length 

(350 m) of the recording array for BHGW2 was slightly longer (fig. 26). Profile BH2 consisted of 174 

recording stations, but recorders were not deployed at 13 stations because they would have blocked 

driveways. We used the same sensors (4.5-Hz), station spacing (2 m), and sampling rate (2 ms) for the 
34 

BHGW2 survey as was used for the BHGW1 survey. However, the seismic source (SP2) for the 

BHGW2 survey was located at SP2, about 80 m southwest of Heath Avenue and about 130 m southeast 

of Santa Monica Boulevard (fig. 26). The first shot started on June 6, 2018, at 22:05:42:36 (local time; 

05:42:36 UTC), and the last shot was completed at 23:01:37 (local time; 06:01:37 UTC). A total of 

about 198 AWD shots were generated. Owing to instrumental failures, we did not obtain data from 19 of 

the 174 seismic recorders.

Santa Monica Fault Data Analysis

The seismic sources for the BHGW1 seismic survey were located about 500 and 647 m 

southwest of the southernmost and northernmost ends of Profile BH1, respectively (fig. 27). We chose 

this site (SP1) to generate seismic sources because it was the location of a previous coring and CPT 

transect, in which an active trace of the Santa Monica Fault was identified. Because the source was not 

centered with respect to the recording array, a difference in travel time from the south end to the north 

end of the array was observed. To evaluate the PGV of the guided waves within the same time window, 

the “moveout” of the travel time was removed by shifting the time of the more distant arrivals on the 

north end of the profile. Thus, the actual travel time of the guided waves on the north end of the 

recording array was greater by about 500 ms than what is shown in figure 27. 

Figure 27. Stacked guided-wave shot gather for BHGW1 seismic survey. Source is located at SP1; recording 

array is located along Profile BH1 (distance between source and recording array ranges from about 500 to about 

650 m). Long propagation distance and high level of cultural noise resulted in poor signal-to-noise ratios. P waves 

(P), S waves (S), and guided waves (GW) are inferred on shot gather. Data were band-pass filtered between 1.5 

and 12 Hz. Location of Charleville Boulevard is shown. Other abbreviation: ms, millisecond(s).
35 

Guided-Wave Data Analysis for Profile BH1 

The signal-to-noise ratio of the data acquired during the BHGW1 seismic survey was low (fig. 

27) owing to excessively high cultural-noise levels during the ~21:00- to ~22:00-hour local time frame 

on May 26, 2018, which was a Saturday evening. However, even with the low signal-to-noise ratios, we 

were able to evaluate PGV of guided waves (fig. 28) within the time frame (>1.5 to 3 s) expected for 

shear-wave and guided-wave arrivals. On the basis of travel time and amplitude, we infer the presence 

of low-velocity guided waves south and north of Charleville Boulevard and possibly near the south end 

of Profile BH1. The observed high values of guided-wave PGV (fig. 28A) correlate with the expected 

guided-wave travel times (fig. 28B). Our data show that the highest PGV values arrived at the recording 

array at about 2,500 ms (2.5 s; ~0.5 s added to arrivals on the north end of the profile shown in fig. 28B), 

and because the source was approximately 650 m from apparent fault zone, this suggests that the guided 

waves traveled at about 250 m/s. The earliest shear waves arrived at the recording array at about 1,500 

ms (1.5 s), suggesting an average VS of about 330 m/s. These velocities suggest that the guided waves 

travel at about 75 percent of the velocity of the shear wave. Along Profile BH1, the most prominent high 

values of PGV are observed between channels 60 and 150 (between meters 118 and 298) of the 

recording array, which extends from slightly south to slightly north of Charleville Boulevard (fig. 28). 

Beverly Hills Profile BH2 Guided-Waves

The signal-to-noise ratios of the data from the BHGW2 seismic survey (fig. 29) were higher than 

those of the data recorded for the BHGW1 survey. As a result, the shear-wave and guided-wave arrivals 

are more apparent on the BHGW2 data. The higher signal-to-noise ratios may have resulted from 

stronger signals because the seismic source (SP2) was closer to the recording array, but the higher ratios 

may also have resulted from lower cultural-noise levels present later in the evening (~22:00 to ~23:00 

local time). Lower noise levels also were likely on a Wednesday evening (June 6, 2018) than on a 

Saturday evening. 

From the data obtained during the BHGW2 seismic survey, we evaluated PGV values of guided 

waves from the time of the shear-wave arrival (~1 s) to about 3.2 s (includes a 0.5-s time shift on the 

north end of the profile; see fig. 30). Our PGV values are averaged over three consecutive arrivals to 

limit large variations from a single arrival. On the basis of travel time and amplitude, the low-velocity 

guided waves appear easy to identify. High-PGV values (fig. 30A) correlate with the expected guidedwave travel times (and velocities) along Profile BH2 (fig. 30B). Our data show that the highest PGV 

values arrived at the recording array at 2,000 to 2,500 ms (2.0–2.5 s; includes the time shift), and, using 

distance from the source (368–510 m) to the fault traces, we found that the guided waves traveled at 

about 185 to 200 m/s. These guided-wave velocities are lower than those estimated for the BHGW1 

survey because of the greater distance and deeper propagation depth of guided waves between SP1 and 

the BHGW1 recording array. The earliest shear wave for the BHGW2 survey arrived at the recording 

array at about 1,500 to 2,000 ms (1.5–2.0 s), suggesting an average VS of about 245 to 255 m/s. This 

suggests that the guided wave travels at about 75 to 78 percent of the velocity of the shear wave. 

Along Profile BH2, the most prominent late-arriving, high-PGV values are seen at stations 

(channels) 120 to 135 (meters 238–268) and 145 to 152 (meters 288–302) of the recording array; these 

stations were located in the vicinity of Charleville Boulevard, suggesting that prominent fault traces are 

present in that area. However, late-arriving, locally high PGV values also were observed near stations 11 

to 28, 78 to 82, and 95 to 102. The high-PGV values observed at these stations also coincide with late 

arrivals that are consistent with guided waves. Similarly PGV-value zones also were seen on the 

BHGW1 survey, which were contaminated with cultural noise. Because of the consistent travel-time 

delays and high amplitudes, we suggest that each of the high-PGV values listed above likely are fault 

related. Because of the prominent PGV peaks and observed travel times (velocities) near Charleville 

Boulevard, we suggest that those probable faults are the ones most directly connected to the fault trace at 
36 

Figure 28. A, Plot of peak ground velocity (PGV) of guided waves for each recording channel along BHGW1 

survey. Highest PGV values (red dots) were concentrated on north end of recording array, both north and south of 

Charleville Boulevard; indications of relatively high values also are present at several locations along Lasky Drive. 

B, Plot of time of arrival of corresponding PGV values shown in A. Note that highest PGV values coincide with 

delayed phases that arrive at about 1.9 to 2.1 seconds (s) or more (after 0.5-s time shift applied). Arrival times have 

been shifted downward on north end of profile by about 0.5 s relative to south end of profile. Owing to low signal-tonoise ratios for BHGW1 survey, uncertainty is high in possible fault traces. Location of Charleville Boulevard is 

shown. Other abbreviations: m, meter(s); ms, millisecond(s); s, second(s).
37 

Figure 29. Stacked guided-wave shot gather for Profile BH2. Source is located at SP2; recording array is located 

along Profile BH1 (distance between source and recording array ranges from about 370 to about 510 m). Shorter 

propagation distance and lower cultural-noise levels resulted in higher signal-to-noise ratios than recorded for 

BHGW1 survey. P waves (P), S waves (S), and guided waves (GW) are inferred on shot gather. Data were bandpass filtered between 1 and 8 Hz. Location of Charleville Boulevard is shown. Other abbreviation: ms, 

millisecond(s).

the seismic source (SP2). The probable fault traces near Charleville Boulevard also are likely to be nearsurface traces. Because multiple high-PGV zones are present along the BHGW2 survey, we suggest that 

the near-surface Santa Monica Fault is distributed along several traces along Lasky Drive.

Summary of Observations, Santa Monica Fault, Beverly Hills

We acquired only guided-wave data along Lasky Drive in Beverly Hills because we did not have 

the requisite permission to conduct in-line, active-source surveys. Additionally, we had little direct 

knowledge of the location of traces of the Santa Monica Fault where we could place our seismic sources. 

As a result, we conducted two guided-wave seismic surveys along Lasky Drive. Before conducting the 

first survey (BHGW1), we did not realize that one of the main traces of the Santa Monica Fault may 

have been located near the intersection of Charleville Boulevard and Lasky Drive, which was the north 

end of the BHGW1 survey. Upon learning of this possible location of the fault trace, we chose to 

conduct a second survey (BHGW2) that extended northward of the possible fault trace. 

The signal-to-noise ratios of data from the BHGW1 survey were low, but the data from that 

survey appear to be consistent with probable faulting north and south of Charleville Boulevard. In 

addition, the data indicate that additional distributed faulting may be present along Profile BH1, 

particularly south of Charleville Boulevard. However, because of the low signal-to-noise ratios of the 

data, we have lower confidence in the data from the BHGW1 survey. 
38 

Figure 30. A, Plot of peak ground velocity (PGV) of guided waves for recording channels along BHGW2 survey. 

Because data were not recorded for some stations and because some sensors were not leveled when deployed, 

we opted to average each PGV value relative to the two closest PGV values to obtain a more stable result. HighPGV values (yellow shading) were concentrated along several locations along Lasky Drive; highest PGV values are 

near Charleville Boulevard. B, Plot of time of arrival of corresponding PGV values shown in A. Arrival times have 

been shifted downward on north end of profile by about 0.5 second (s) relative to south end of profile. Highest PGV 

values coincide with delayed phases that arrive at about 2 s or more (shifted time), consistent with guided waves, 

suggesting prominent faulting near Charleville Boulevard, but additional faulting appears to be present at areas 

along the profile (yellow shading). Location of Charleville Boulevard is shown. Other abbreviations: m, meter(s); ms, 

millisecond(s); s, second(s).
39

Data from the BHGW2 survey contained much higher signal-to-noise ratios, and the BHGW2 

data also are indicative of faulting near the intersection of Charleville Boulevard and Lasky Drive. In 

addition, the BHGW2 data also are consistent with the presence of as many as three other fault traces 

along Lasky Drive. Importantly, all five of these high-PGV zones can be inferred on both the BHGW1 

and BHGW2 data (figs. 28, 30). Thus, we suggest that distributed shallow-depth faulting likely is 

present at several locations along Lasky Drive.

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