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Using Twelve Years of USGS Refraction Lines to Calibrate the Brocher and others (1997) 3D Velocity Model of the Bay Area

  • January 2004
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John Boatwright
John Boatwright
Luke Blair
Luke Blair
Luke Blair
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Rufus Catchings at United States Geological Survey
Rufus Catchings
Mark Goldman
Mark Goldman
Mark Goldman
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Abstract and Figures

Campbell (1983) demonstrated that site amplification correlates with depths to the 1.0, 1.5, and 2.5 km/s S-wave velocity horizons. To estimate these depths for the Bay Area stations in the PEER/NGA database, we compare the depths to the 3.2 and 4.4 km/s P-wave velocities in the Brocher and others (1997) 3D velocity model with the depths to these horizons determined from 6 refraction lines shot in the Bay Area from 1991 to 2003. These refraction lines range from two recent 20 km lines that extend from Los Gatos to downtown San Jose, and from downtown San Jose into Alum Rock Park, to two older 200 km lines than run axially from Hollister up the San Francisco Peninsula to Inverness and from Hollister up the East Bay across San Pablo Bay to Santa Rosa. Comparison of these cross-sections with the Brocher and others (1997) model indicates that the 1.5 km/s S-wave horizon, which we correlate with the 3.2 km/s P-wave horizon, is the most reliable horizon that can be extracted from the Brocher and others (1997) velocity model. We determine simple adjustments to bring the Brocher and others (1997) 3.2 and 4.4 km/s P-wave horizons into an average agreement with the refraction results. Then we apply these adjustments to estimate depths to the 1.5 and 2.5 km/s S-wave horizons beneath the strong motion stations in the PEER/NGA database.
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Using Twelve Years of USGS Refraction Lines to
Calibrate the Brocher and others (1997) 3D Velocity
Model of the Bay Area
John Boatwright1, Luke Blair1 Rufus Catchings1, Mark Goldman1,
Fabio Perosi1, and Clare Steedman1
Open-File Report 2004-1282
2004
Any use of trade, firm, or product names is for descriptive purposes only and does not
imply endorsement by the U.S. Government.
U.S. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY
1U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, CA 94025
Abstract
Campbell (1983) demonstrated that site amplification correlates with
depths to the 1.0, 1.5, and 2.5 km/s S-wave velocity horizons. To
estimate these depths for the Bay Area stations in the PEER/NGA
database, we compare the depths to the 3.2 and 4.4 km/s P-wave
velocities in the Brocher and others (1997) 3D velocity model with the
depths to these horizons determined from 6 refraction lines shot in the
Bay Area from 1991 to 2003. These refraction lines range from two
recent 20 km lines that extend from Los Gatos to downtown San Jose,
and from downtown San Jose into Alum Rock Park, to two older 200
km lines than run axially from Hollister up the San Francisco
Peninsula to Inverness and from Hollister up the East Bay across San
Pablo Bay to Santa Rosa. Comparison of these cross-sections with the
Brocher and others (1997) model indicates that the 1.5 km/s S-wave
horizon, which we correlate with the 3.2 km/s P-wave horizon, is the
most reliable horizon that can be extracted from the Brocher and
others (1997) velocity model. We determine simple adjustments to
bring the Brocher and others (1997) 3.2 and 4.4 km/s P-wave horizons
into an average agreement with the refraction results. Then we apply
these adjustments to estimate depths to the 1.5 and 2.5 km/s S-wave
horizons beneath the strong motion stations in the PEER/NGA
database.
Introduction
Brocher et al. (1997) applied the method of Jachens and Moring (1990) to
invert the isostatic gravity anomaly for the thickness of the Cenozoic
sediments throughout the Bay Area. The inversion uses gravity observa-
tions made directly on basement and sediments and assumes a single
density-depth function within the Cenozoic basins. The inversion also
assumes vertical faults and cannot resolve overthrust geometries within the
basins. They combined this sedimentary model with a geologic model of
the major faults in the region to determine a 3D model that extends down to
the Moho. By assigning velocity gradients to the basin fills and the bedrock
blocks, they were able to assemble the first complete 3D Vp and Vs
velocity model for the Bay Area.
The Brocher et al. (1997) 3D model is a remarkable product, and it has
performed well as a 1st order model for seismic velocities in the Bay Area.
However, the models for the Cenozoic basins depend explicitly on the
average density-depth and velocity-depth functions determined by Brocher
et al. (1997) and Tiballi and Brocher (1998) from industry borehole wells
that were largely sited in the Livermore and San Pablo basins. Recently,
we have re-picked and re-inverted 10 refraction lines shot by the USGS in
the Bay Area from 1980 to 2003. The velocity cross-sections obtained
from these refraction lines allow us to recalibrate the Brocher et al. (1997)
velocity model.
Figure 1 shows the seven most recent refraction lines, along with the cutout
volumes from the 3D model that we used for comparison. The black bars
locate the cross-sections where we show direct comparisons of the models,
with the Figures for these comparisons labeled.
Method of Comparison
The object of this report is to estimate the depths to the 1.0, 1.5, and 2.5
km/s S-wave velocities beneath the strong motion stations in the Bay Area.
from the Brocher et al. (1997) model. In general, the S-wave velocities in
the Brocher et al. (1997) model are generated from the P-wave velocities,
which are prescribed as functions of depth in four different volumes. To
calibrate the Brocher et al. (1997) estimates, we first determine that Vp
velocities of 3.2 and 4.4 km/s correspond to Vs velocities of 1.5 and 2.5
km/s. We also find that we cannot resolve the Vs = 1.0 km/s horizon from
the P-wave refraction results because of the marked variation of Vp/Vs
between near-surface soil and rock. Then we compare the depths to these
Vp velocities from the Brocher et al. (1997) model against the P-wave
refraction results recently obtained by Catchings (see Addendum). In
general, the Brocher et al. (1997) model is slower than the refraction
models. We derive corrections for the Brocher et al. (1997) model that are
linear functions of depth, and use these corrections to revise the depths to
the Vs = 1.5 and 2.5 km/s horizons beneath the strong motion stations.
Figure 2 compares S-wave velocities obtained by Catchings et al. (2004)
for the line running from Los Gatos to downtown San Jose to the cutout of
the Brocher et al. (1997) model. The comparison is masked where the ray
coverage is sparse. The contour lines show 1.0, 1.5, and 2.5 km/s S-wave
horizons from the refraction results, while the colored background indi-
cates the same S-wave velocities in the Brocher et al. (1997) model. The
fit of the 1.5 km/s horizon with the green-orange boundary is quite good,
although the Brocher et al. (1997) model is almost always deeper.
In contrast, the fit of the 2.5 km/s boundary is poor and spatially variable.
We assume that this misfit results from the lack of resolution of the deeper
sections of the basins in the Brocher at al. (1997) model. This lack of
resolution occurs for two reasons. First, the isostatic gravity anomaly from
these sections is weaker because the density difference between the deeper
sediments and the basement is smaller, and second, any consistent misfit of
the assumed density function in the shallow section will project into a
larger misfit in the deeper section.
Unfortunately, the Los Gatos line is the only refraction line on which S-
waves could be picked and inverted. To incorporate the velocity structure
obtained from the other refraction lines, it is necessary to compare P-wave
velocities. For this comparison, we choose P-wave velocities of 2.4, 3.2,
and 4.4 km/s as analogs to the S-wave velocities of 1.0, 1.5, and 2.5 km/s.
Our choice of Vp = 2.4 km/s as the analog for Vs = 1.0 km/s is derived by
averaging Vp's that correspond to Vs =1.0 km/s from the shallow borehole
results compiled by Boore (2003), shown in Figure 3. We note, however,
that this result applies to shallow rock layers rather than buried sedimentary
layers, for which Brocher et al. (1997) used the relation shown at the top
of the plot. The marked difference between rock and sediment Vp/Vs,
coupled with the sparse sampling of the Vp = 2.4 km/s horizon in the
refraction lines obviates correcting the Vs = 1.0 km/s horizon from the
Brocher et al. (1997) model using the P-wave refraction results.
Our choices of Vp = 3.2 and 4.4 km/s as analogs for Vs = 1.5 and 2.5 km/s
are obtained by overlaying the Catchings et al. (2004) S-wave and P-wave
results for the Los Gatos refraction line, and simply averaging the Vp esti-
mates along the Vs = 1.5 and 2.5 contours. Catchings et al.'s (2004) Vp
contours are plotted against the Brocher et al. (1997) velocities in Figure 4.
We note that while the P-wave velocity of 3.2 km/s yields a good overall
fit to the S-wave velocity of 1.5 km/s, the Vp/Vs ratio varies systematically
along the eastern segment of this line.
Figures 5-9 show the comparison of the refraction P-wave velocity hori-
zons with the P-wave velocities in the Brocher et al. (1997) model for the
other cross-sections. Figure 5 shows the line across the Evergreen Basin
that was shot in May 2003. The correspondence to the west of the basin, in
the saddle underlying San Jose, is excellent, while the fit to the east is
weaker. The Los Gatos and Evergreen lines, shot in 2000 and 2003, are
the most densely sampled lines, with receivers at 50 m spacing. This dense
spacing of receivers yields an excellent resolution of the near-surface
velocity structure.
The receiver spacing for the 1991-1993 lines was about 1 km, which is
significantly coarser than the 50 m spacing for the later lines. This coarse
spacing yields a much poorer resolution of the near-surface velocity
structure. Figure 6 shows an extreme example of this lack of resolution,
for the so-called central section of the East-Bay line. Only the 4.4 km/s
Vp contour can be discerned in this cross-section. The apparent variation
in the Brocher et al. (1997) model results from the refraction line running
along a volume boundary and the volumetric averaging used to determine
the Brocher et al. (1997) model cross-sections.
Further north, on either side of San Pablo Bay, the P-wave horizons in
Figure 7 are in much better agreement, although the refraction lines do not
image the deeper basin structure inferred from the gravity inversion. The
masked area in the middle of the cross-section underlies San Pablo Bay,
where a set of OBS instruments failed to record usable signals.
The eastern section of the Cross-Bay line, shown in Figure 8, is the only
cross-section where the 4.4 km/s P-wave velocity obtained by the
refraction line is clearly deeper that estimated by Brocher et al. (1997).
The low velocities associated with the Livermore basin appear to start as
far west as the Hayward fault. However, the 3.2 km/s contour is still
shallower than the Brocher et al. (1997) estimate, reaffirming our choice of
this intermediate velocity as the most stable marker.
Finally, the western section of the Cross-Bay line is shown in Figure 9.
Here the refraction profile does not see the bedrock velocity contrast that
Brocher et al. (1997) incorporate across the San Andreas fault. Equally
surprising is the apparent basement saddle that underlies the southern San
Francisco Bay, on the right of the cross section.
Adjusting the Brocher et al. (1997) Model
To estimate depths to the 1.5 km/s S-wave horizon, we will adjust the
Brocher et al. (1997) model as simply as possible. First, we regress the
difference between the 3.2 km/s depths from the two models as a linear
function of depth, that is, as
χ
232 32 2
=
()
−
()
−
()
∑zxbzxc
RiBi.. (1)
where
zx
Bi32.
()
is the depth of the 3.2 km/s P-wave velocity in the Brocher
et al. (1997) model, and
zx
Ri32.
()
is the depth obtained from the refraction
studies. Sample points xi were chosen at 1 km spacing for the Los Gatos
and Evergreen lines, and 3 km spacing for the Peninsula, East Bay, and
Cross Bay lines. For the Peninsula, East Bay and Cross Bay lines, we did
not use the
zx
Ri32.
()
estimates where they were above the elevation of the
free surface. These misestimates result from the lack of resolution of the
near-surface velocities and the smoothing of the tomographic inversion.
The simple linear parameterization as a function of depth in equation (1)
corresponds adequately with the velocity-depth functions assumed by
Brocher's et al. (1997). Figure 10 shows the comparison of
zx
Bi32.
()
and
zx
Ri32.
()
. Because the Brocher et al. (1997) model is a series of bounded
volumes with prescribed rules for the velocity as a function of depth, the
3.2 km/s P-wave velocity occurs only at depths of about 0.1, 0.7, and 1.6
km, depending on the volume the refraction line transects. Slight varia-
tions from these depths occur because the P-wave velocity is being sampled
within a volume around the refraction lines. Regressing
zR
32.
on
zB
32.
yields
the result
zz
RB
32 32
0 164 0 352
..
= . + . (2)
with the associated uncertainties
σ
(zz
RR
32 32
0
..
) .65≈ . (3)
Similarly, regressing
zR
44.
on
zB
44.
yields
zz
RB
44 44
06 04
..
= . 79 + . 17 (4)
with the associated uncertainties
σ
(zz
RR
44 44
0
..
) .45≈ . (5)
Table 1 contains the Excel Worksheet for the PEER/NGA stations that fall
within the area of the 3D velocity model. We use the adjustments given
above to correct the depths of the 3.2 and 4.4 km/s P-wave horizons
obtained from the Brocher et al. (1997) model. We also estimate the
uncertainty of these depths.
In addition, we have estimated the depth to these horizons directly from the
refraction data for those stations within 5 km of a refraction line. More
than half (71 out of 133) of the stations are sufficiently close to a
refraction line to directly estimate the depth to the Vp = 3.2 and 4.4 km/s
horizon. However, for 58 of these 71 stations, the Vp = 3.2 km/s horizon
was determined from the tomographic inversions of the P-wave arrival
times to be above the elevation of the station. These misestimates are
generally derived for the stations near the Peninsula, East Bay, and Cross
Bay lines, and result from the lack of resolution of near-surface velocities
and the smoothing of the tomographic inversion. We consider these esti-
mates of
zR
32.
to be relatively weak and leave the EXCEL element empty.
Finally, in Table 2, we compile estimates of the depth to the Vs = 1.0 and
1.5 km/s horizons for seven strong motion stations that are sufficiently
close to boreholes that penetrate to these velocities. We also indicate the
number of the borehole assigned by Boore (2003). Unfortunately, there
are no direct comparisons of depth to Vp = 3.2 km/s from refraction lines
and borehole estimates of depth to Vs = 1.5 km/s. In general, the Brocher
et al. (1997) estimate of the depth to Vp = 3.2 km/s for these stations was
0.64 km, which we have corrected to 0.39 km. This estimate appears quite
deep, relative to these borehole sites underlain by shallow rocks, but we
presume that the requirement that the boreholes directly sample Vs = 1.0
km/s material introduces a strong sampling bias. We note, as well, that this
compilation may be incomplete, as it is derived from Boore's (2003)
compilation of borehole velocity results, and does not include all the
borehole velocity structures that have been obtained in the Bay Area.
Conclusions
We have compared the velocities in the Brocher et al. (1997) 3D model to
the velocity structures obtained from the inversion of more than 500 km of
refraction lines shot in the Bay Area from 1991 to 2003. In general, the
velocities in the Brocher 3D model are slower than the velocities inferred
from the refraction lines. We have determined simple corrections, that is,
Δz(z), for the depths to the Vp = 3.2 and 4.4 km/s horizons estimated from
the Brocher et al. 3D model and compiled these corrected depths for the
strong motion stations in the Bay Area in the PEER/NGA database. We
have also compiled the depths to these horizons beneath those stations
within 5 km of the refraction lines, where these velocity structures can be
inverted directly. Finally, we have added a table showing the depth to Vs =
1.0 and 1.5 km/s for seven stations where it was obtained directly from
boreholes.
Acknowledgements
The authors are grateful for the rapid and thorough reviews of this report
provided by Paul Spudich and Shane Detweiler. The online database of
borehole velocities compiled by Dave Boore provided a critical grounding
for many of the geophysical interpretations in this paper.
This project was sponsored by the Pacific Earthquake Engineering Research
Center's Program of Applied Earthquake Engineering Research of Lifeline
Systems supported by the California Energy Commission, California
Department of Transportation, and the Pacific Gas & Electric Company.
The financial support of the PEARL sponsor organizations including the
Pacific Gas & Electric Company, the California Energy Commission, and
the California Department of Transportation is acknowledged. This work
made use of Earthquake Engineering Research Centers Shared Facilities
supported by the National Science Foundation under Award Number EEC-
9701568.
Legal Notice
This report was prepared as a result of work sponsored by the California
Energy Commission (Commission). It does not necessarily represent the
view of the Commission, its employees, or the State of California. The
Commission, the State of California, its employees, Contractors and
subcontractors make no warranty, express or implied, and assume no legal
liability for the information in this report; nor does any party represent that
the use of this information will not infringe upon privately owned rights.
This report has not been approved or disapproved by the Commission nor has
the commission passed upon the accuracy or adequacy of the information in
this report.
Bibliography
Boore, D.M., (2003). P- and S- Velocities from Surface-to-Borehole
Logging, http://quake.wr.usgs.gov/~boore/data_online.htm.
Brocher, T.M., E.E. Brabb, R.D. Catchings, G.S. Fuis, T.E. Fumal, R.C.
Jachens, A.S. Jayko, R.E. Kayen, R.J. McLaughlin, Tom Parsons,
M.J. Rymer, R.G. Stanley, C.M. Wentworth, (1997). A crustal-scale
3-D seismic velocity model for the San Francisco Bay area,
California, Eos, vol.78, no.46, Suppl., pp.435-436.
Campbell, Kenneth W, (1983). The effects of site characteristics on near-
source recordings of strong-ground motion. Hays, Walter W. (ed.),
Kitzmiller, Carla, and Darnell, Diana, A workshop on site-specific
effects of soil and rock on ground motion and the implications for
earthquake-resistant design, Open-file Report 83-0845.
Catchings, R.D., G. Gandhok, M.R. Goldman, R. Hansen, and R.
McLaughlin (2004). Basin structure and velocities from the 2000
Santa Clara Seismic Investigation (SCSI) as related to earthquake
hazards and water resources, western Santa Clara Valley, California,
U.S. Geological Survey Open-File Report 04-xxx.
Jachens, R.C., and B.C. Moring (1990). Maps of the thickness of Cenozoic
deposits and the isostatic residual gravity over basement for Nevada,
U.S. Geological Survey Open-File Report 90-496, 11 p.
Tiballi, C.A., and T.M. Brocher (1998). Compilation of 71 additional sonic
and density logs from 59 oil test wells in the San Francisco Bay area,
U.S. Geological Survey Open-File Report 98-615, 131 p.
Table Captions
Table 1. Estimated depths to Vp = 3.2 and 4.4 km/s horizons beneath the
Bay Area stations in the PEER/NGA database. The sequence #, station #,
and descriptive station name are taken from the PEER/NGA database,
although some station names have been edited for brevity. The station
elevation (Elev) is in km. The first column labeled as (Brchr Vp) contains
the P-wave velocity in km/s for the horizon whose depth is given in the
following (Brchr Z(3.2)) column. The (Brchr Z(3.2)) column contains the
Brocher et al. (1997) estimate of depth in km of the Vp = 3.2 km/s horizon
beneath the station. The column labeled (Brchr Z'(3.2)) contains the adjus-
ted estimate of the depth in km to the Vp = 3.2 km/s horizon obtained
from equation (2). The column labeled (Brchr dZ(3.2)) contains the un-
certainty in km obtained from equation (3). Similarly, the second column
labeled as (Brchr Vp) contains the P-wave velocity in km/s for the horizon
whose depth is given in the following (Brchr Z(4.4)) column. The column
labeled (Brchr Z(4.4)) contains the Brocher et al. (1997) estimate of the
depth in km to the Vp = 4.4 km/s horizon beneath the station. The column
labeled (Brchr Z'(4.4)) contains the adjusted estimate of the depth in km to
the Vp = 4.4 km/s horizon obtained from equation (4). The column label-
ed (Brchr dZ(4.4)) contains the uncertainty in km obtained from equation
(5). The columns labeled (Rfrct Z(3.2)) and (Rfrct Z(4.4)) contain the
estimates of the depths in km to the Vp = 3.2 and 4.4 km/s horizons infer-
red obtained directly from refraction lines that fall within 5 km of the
station. Finally, the column labeled (Offset) contains the offset in km of
the strong motion station from the refraction line used to estimate (Rfrct
Z(3.2)) and (Rfrct Z(4.4))
Table 2. Depths to the Vs = 1.0 and 1.5 km/s horizons beneath seven Bay
Area stations in the PEER/NGA database, obtained directly from borehole
logging.. The sequence #, station #, and descriptive station name are taken
from the PEER/NGA database. The column labeled (Boore #) contains the
number of the borehole in the Boore (2003) database. The columns label-
ed (Borehole Z(Vs=1.0)) and (Borehole Z(Vs=1.5)) contain the depths in
km to the Vs = 1.0 and 1.5 km/s horizons determined in the boreholes.
The column labeled (Refraction Z(Vp=4.4)) contains the estimates of the
depth in km of the Vp = 4.4 km/s horizon inferred from the refraction line.
No estimates of the depth to the Vp = 3.2 km/s horizon were available for
these stations. Finally, the column labeled (Distance from Line) contains
the offset of the station from the refraction line.
Table 1
Seq # Sta # Station Name Latitude Longitude Elev Brchr Brchr Brchr Brchr Brchr Brchr Brchr Brchr Rfrct Rfrct Offset
Vp Z(3.2) Z'(3.2) dZ(3.2) Vp Z(4.4) Z'(4.4) dZ(4.4) Z(3.2) Z(4.4)
427 57066 Agnews State Hospital 37.39 -121.95 3.17 0.67 0.40 0.26 4.41 2.25 1.62 0.73
1157 1756 Alameda - Oakland Air 37.73 -122.25 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1156 1755 Alameda Fire Station #1 37.76 -122.24 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
569 99999 Alameda Naval Air Stn 37.78 -122.30 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
170 1652 Anderson Dam (Dwnstrm) 37.16 -121.62 0.18 3.16 0.66 0.40 0.26 4.41 2.25 1.62 0.73 2.41 1.59
171 1652 Anderson Dam (L Abut) 37.16 -121.62 0.18 3.16 0.66 0.40 0.26 4.41 2.25 1.62 0.73 2.41 1.59
458 58373 APEEL 10 - Skyline 37.46 -122.34 3.15 0.65 0.39 0.26 4.41 2.25 1.62 0.73
460 58376 APEEL 1E - Hayward 37.62 -122.13 3.14 0.65 0.39 0.26 4.41 2.25 1.62 0.73
119 1002 APEEL 2 - Redwood City 37.52 -122.25 0.00 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 0.00 2.76
462 58393 APEEL 2E Hayward Muir 37.65 -122.08 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
450 58219 APEEL 3E Hayward CSUH 37.65 -122.06 0.13 3.13 0.49 0.34 0.22 4.30 1.40 1.26 0.57 1.49 3.66
461 58378 APEEL 7 - Pulgas 37.48 -122.31 0.12 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.00 4.24
144 1161 APEEL 9 - Crystal Springs 37.47 -122.32 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1448 47750 Aptos - Sea Cliff Array 36.97 -121.90 0.02 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49 0.30 1.78 1.38
455 58262 Belmont - Envirotech 37.51 -122.30 0.15 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 0.55 1.99
1160 1760 Benicia Fire Station #1 38.05 -122.15 4.05 0.25 0.25 0.16 4.29 1.29 1.22 0.55
463 58471 Berkeley LBL 37.87 -122.24 0.24 3.21 1.62 0.73 0.48 4.38 3.63 2.19 0.99 2.28 4.22
14 13 BRAN 37 .04 -121.98 3.29 0.12 0.21 0.13 4.47 1.00 1.10 0.49
400 47125 Capitola 36.97 -121.95 0.00 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49 0.28 1.81 2.41
424 57007 Corralitos 37.05 -121.80 0.42 3.21 1.62 0.73 0.48 4.39 3.13 1.98 0.89 1.11 1.73
436 57504 Coyote Lake Dam Dwnstrm 37.12 -121.55 0.21 3.21 0.68 0.40 0.26 4.41 2.25 1.62 0.73 2.86 1.55
431 57217 Coyote Lake Dam SW Abut 37.11 -121.55 0.24 3.17 0.66 0.40 0.26 4.41 2.25 1.62 0.73 2.89 1.32
1141 1720 Cupertino - Sunnyvale Rod 37.29 -122.08 0.22 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 0.27 0.95
1137 1690 Danville Fire Station 37.81 -121.99 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
146 1265 Del Valle Dam (Toe) 37.62 -121.75 3.21 1.62 0.73 0.48 4.40 2.87 1.88 0.84
1136 1689 Dublin - Fire Station 37.70 -121.93 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
1460 58664 Dumbarton Bridge West 37.49 -122.13 0.00 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 1.88 3.59
1144 1737 El Cerrito - Mira Vista CC 37.93 -122.30 0.20 3.20 1.48 0.68 0.45 4.39 3.43 2.11 0.95 2.94 4.45
459 58375 Foster City - APEEL 1 37.54 -122.23 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
1154 1753 Foster City - Bowditch Sch 37.56 -122.24 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
1456 57784 Fremont - 2 Story City Lbr 37.55 -121.97 0.02 3.18 0.67 0.40 0.26 4.41 2.25 1.62 0.73 0.30 3.59
Seq # Sta # Station Name Latitude Longitude Elev Brchr Brchr Brchr Brchr Brchr Brchr Brchr Brchr Rfrct Rfrct Offset
Vp Z(3.2) Z'(3.2) dZ(3.2) Vp Z(4.4) Z'(4.4) dZ(4.4) Z(3.2) Z(4.4) Offset
1457 57948 Fremont - 2 Story Ind Bldg 37.47 -121.92 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73
1151 1750 Fremont - Coyote Hills 37.55 -122.09 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
177 1686 Fremont - Emerson Court 37.53 -121.92 0.06 4.04 1.11 0.55 0.36 4.39 2.14 1.57 0.71 1.24 4.45
426 57064 Fremont - MSJ 37.53 -121.91 0.09 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73 1.11 0.99
399 47006 Gilroy - Gavilan Coll. 36.97 -121.56 3.12 0.64 0.39 0.25 4.41 2.25 1.62 0.73
435 57476 Gilroy - Historic Bldg. 37.00 -121.56 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
406 47379 Gilroy Array #1 36.97 -121.57 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
407 47380 Gilroy Array #2 36.98 -121.55 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
408 47381 Gilroy Array #3 36.98 -121.53 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
432 57382 Gilroy Array #4 37.00 -121.52 0.05 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 2.43 3.81
433 57383 Gilroy Array #6 37.02 -121.48 0.32 3.20 1.60 0.73 0.47 4.42 2.29 1.63 0.74 2.65 0.54
434 57425 Gilroy Array #7 37.03 -121.43 0.31 3.12 0.65 0.39 0.26 4.40 2.87 1.88 0.84 0.38 2.72 4.64
176 1678 Golden Gate Bridge 37.80 -122.47 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
142 1117 Golden Gate Park 37.77 -122.48 0.06 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 1.37 3.67
1462 58964 Half Moon Bay - Array 37.36 -122.39 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
430 57191 Halls Valley 37.33 -121.71 0.46 3.13 0.65 0.39 0.26 4.40 2.40 1.68 0.76 1.38 2.54
464 58498 Hayward - BART Sta 37.67 -122.08 0.03 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 1.40 4.72
1155 1754 Hayward FS #1 37.67 -122.08 0.02 3.13 0.63 0.39 0.25 4.29 1.37 1.25 0.56 1.39 4.24
1172 1797 Hollister - Airport #3 36.89 -121.40 0.06 3.91 1.47 0.68 0.44 4.40 2.77 1.83 0.83 2.40 1.85
1131 1575 Hollister - City Hall Annex 36.85 -121.40 0.08 3.18 1.58 0.72 0.47 4.43 2.30 1.64 0.74 3.68 1.67
128 1032 Hollister - SAGO Vault 36.76 -121.44 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49
409 47524 Hollister - South & Pine 36.84 -121.39 0.08 3.13 1.50 0.69 0.45 4.40 2.65 1.78 0.80 3.68 1.58
127 1028 Hollister City Hall 36.85 -121.40 0.08 3.13 1.50 0.69 0.45 4.41 2.40 1.68 0.76 3.68 1.63
174 1656 Hollister Diff Array #1 36.88 -121.41 0.07 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73 2.46 2.66
174 1656 Hollister Diff Array #3 36.88 -121.41 0.07 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73 2.46 2.66
174 1656 Hollister Diff Array #4 36.88 -121.41 0.07 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73 2.46 2.66
174 1656 Hollister Diff Array #5 36.88 -121.41 0.07 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73 2.46 2.66
174 1656 Hollister Diff. Array 36.88 -121.41 0.07 3.13 1.50 0.69 0.45 4.41 2.25 1.62 0.73 2.46 2.66
1132 1590 Larkspur Ferry Terminal 37.94 -122.50 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
17 16 LGPC 37 . 1 7 -122.01 0.44 3.21 1.55 0.71 0.46 4.39 3.34 2.07 0.93 0.16 0.72 0.38
437 0 Livermore - Fagundas 37.75 -121.77 0.19 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01 0.00 1.83 1.36
438 0 Livermore - Morgan Park 37.81 -121.79 0.62 4.05 0.25 0.25 0.16 4.29 1.29 1.22 0.55 0.31 2.15 5.00
1451 57180 Los Gatos - Lexington Dam 37.20 -121.99 0.21 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.19 1.06 0.21
1139 1697 Los Gatos - Los Altos Rod 37.23 -122.10 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
Seq # Sta # Station Name Latitude Longitude Elev Brchr Brchr Brchr Brchr Brchr Brchr Brchr Brchr Rfrct Rfrct Offset
Vp Z(3.2) Z'(3.2) dZ(3.2) Vp Z(4.4) Z'(4.4) dZ(4.4) Z(3.2) Z(4.4) Offset
1458 58233 Lower Crystal Springs 37.52 -122.36 0.06 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 1.32 4.50
1167 1784 Menlo Park - USGS #11 37.45 -122.17 0.01 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 3.74 3.41
1149 1745 Menlo Park - USGS #15 37.45 -122.16 0.01 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 3.74 3.23
405 47377 Monterey City Hall 36.59 -121.89 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49
1158 1758 Morgan Hill - El Toro FS 37.14 -121.66 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1162 1762 Novato Fire Station #1 38.09 -122.56 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1152 1751 Novato Fire Station #4 38.06 -122.53 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
1459 58472 Oakland - Outer Harbor 37.81 -122.31 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
453 58224 Oakland - Title & Trust 37.80 -122.26 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
456 58264 Palo Alto - 1900 Embar 37.45 -122.11 0.00 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 2.86 0.89
1169 1787 Palo Alto - FS #7 SLAC 37.41 -122.20 0.09 3.14 0.65 0.39 0.26 4.41 2.25 1.62 0.73 1.27
162 1601 Palo Alto - SLAC Lab 37.42 -122.21 0.10 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.00 1.44
457 58338 Piedmont Jr High 37.82 -122.23 3.13 0.65 0.39 0.26 4.40 2.21 1.60 0.72
1138 1691 Pleasant Hill FS #2 37.92 -122.07 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
1168 1785 Pleasanton FS #1 37.66 -121.87 0.10 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01 1.56 1.57
439 58043 Point Bonita 37.82 -122.52 0.04 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.20 3.93
1150 1749 Richmond - Point Molate 37.95 -122.41 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
465 58505 Richmond City Hall 37.93 -122.34 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1142 1722 Richmond Rod & Gun Club 37.97 -122.36 3.18 1.58 0.72 0.47 4.41 2.25 1.62 0.73
403 47189 SAGO South - Surface 36.75 -121.39 3.28 0.17 0.22 0.15 4.46 1.61 1.35 0.61
1449 47762 Salinas - County Hospital 36.69 -121.63 4.22 1.00 0.52 0.34 4.61 1.14 1.15 0.52
402 47179 Salinas - John & Work 36.67 -121.64 3.13 1.50 0.69 0.45 4.66 1.25 1.20 0.54
1143 1735 San Francisco - 9th Circ 37.77 -122.41 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1133 1675 San Francisco - FS #17 37.72 -122.38 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
1166 1774 San Francisco - FS #2 37.76 -122.50 0.01 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 1.21 1.36
1146 1741 San Francisco - Marina 37.80 -122.44 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1453 57600 San Jose - Emory & Bell 37.32 -121.93 0.03 3.99 1.31 0.63 0.41 4.41 2.25 1.62 0.73 0.76 1.97 1.31
1454 57604 San Jose - S Clara Bldg 37.35 -121.90 0.01 3.33 0.75 0.43 0.28 4.41 2.25 1.62 0.73 0.53 1.95 1.74
1452 57563 San Jose - Santa Teresa 37.21 -121.80 0.22 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.38 1.66 2.42
1147 1742 San Jose - Weather Sta 37.35 -121.90 0.01 3.19 0.68 0.40 0.26 4.41 2.25 1.62 0.73 0.51 1.95 1.39
401 47126 San Juan Bautista 36.86 -121.54 0.05 3.24 1.00 0.52 0.34 4.40 3.07 1.96 0.88 3.65 2.09
172 1655 San Justo Dam (L Abut) 36.82 -121.44 0.14 3.21 1.62 0.73 0.48 4.49 2.57 1.75 0.79 3.73 2.27
173 1655 San Justo Dam (R Abut) 36.82 -121.44 0.14 3.21 1.62 0.73 0.48 4.49 2.57 1.75 0.79 3.73 2.27
429 57187 San Ramon - Eastman 37.72 -121.92 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
Seq # Sta # Station Name Latitude Longitude Elev Brchr Brchr Brchr Brchr Brchr Brchr Brchr Brchr Rfrct Rfrct Offset
Vp Z(3.2) Z'(3.2) dZ(3.2) Vp Z(4.4) Z'(4.4) dZ(4.4) Z(3.2) Z(4.4) Offset
428 57134 San Ramon Fire Station 37.78 -121.98 3.21 1.62 0.73 0.48 4.38 3.75 2.24 1.01
1455 57748 Santa Clara - 237/Alviso 37.42 -121.97 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
1450 48906 Santa Cruz - Co Office 36.97 -122.02 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49
440 58065 Saratoga - Aloha Ave 37.25 -122.03 0.16 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.23 0.25
454 58235 Saratoga - W Valley Coll. 37.26 -122.00 0.11 3.21 1.61 0.73 0.47 4.39 3.14 1.99 0.89 0.18 1.86
454 58235 Saratoga - WVC E Wall 37.26 -122.00 0.11 3.21 1.61 0.73 0.47 4.39 3.14 1.99 0.89 0.18 1.86
454 58235 Saratoga - WVC NE 37.26 -122.00 0.11 3.21 1.61 0.73 0.47 4.39 3.14 1.99 0.89 0.18 1.86
454 58235 Saratoga - WVC SE 37.26 -122.00 0.11 3.21 1.61 0.73 0.47 4.39 3.14 1.99 0.89 0.18 1.86
454 58235 Saratoga - WVC Wall 37.26 -122.00 0.11 3.21 1.61 0.73 0.47 4.39 3.14 1.99 0.89 0.18 1.86
445 58132 SF - Cliff House 37.77 -122.51 0.00 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 0.97 1.88
443 58130 SF - Diamond Heights 3 7.74 -122.43 0.14 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 2.04 4.95
444 58131 SF - Pacific Heights 37.79 -122.42 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
451 58222 SF - Presidio 37.79 -122.45 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
448 58151 SF - Rincon Hill 37.78 -122.39 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
446 58133 SF - Telegraph Hill 37.80 -122.40 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
452 58223 SF Intern. Airport 37.62 -122.39 0.00 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 1.73 0.74
404 47315 SJB Overpass, 3 36.86 -121.57 0.12 3.19 1.60 0.73 0.47 4.51 1.04 1.11 0.50 3.47 3.15
404 47315 SJB Overpass, 5 36.86 -121.57 0.12 3.19 1.60 0.73 0.47 4.51 1.04 1.11 0.50 3.47 3.15
466 58539 South SF, Sierra Pt. 37.67 -122.38 0.01 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73 2.12 3.57
18 17 Stanford Park. Garage 37.43 -122.17 0.02 3.14 0.65 0.39 0.26 4.41 2.25 1.62 0.73 0.00 5.31 1.58
178 1695 Sunnyvale - Colton Ave. 37.40 -122.02 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73
1135 1688 Sunol - Forest FS 37.59 -121.88 3.21 1.62 0.73 0.48 4.29 1.40 1.26 0.57
1134 1684 Sunol - Ohlone Wilderness 37.51 -121.83 0.12 3.12 0.64 0.39 0.25 4.35 2.19 1.59 0.72 0.20 4.76
441 58117 Treasure Island 37.82 -122.37 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
441 58642 Treasure Island Array 37.82 -122.37 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
16 15 UCSC 37 .0 0 -122.06 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49
447 58135 UCSC Lick Observatory 37.00 -122.06 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49
1145 1739 Union City - Masonic 37.60 -122.00 0.07 3.13 0.63 0.39 0.25 4.31 1.54 1.32 0.59 2.91
1159 1759 Vallejo FS #1 38.10 -122.24 4.05 0.25 0.25 0.16 4.29 1.29 1.22 0.55
15 14 WAHO 36.97 -121.99 3.29 0.12 0.21 0.13 4.46 1.00 1.10 0.49
442 58127 Woodside 37.42 -122.25 0.11 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 4.15
1153 1752 Woodside - Filoli Center 37.46 -122.30 0.12 3.13 0.65 0.39 0.26 4.41 2.25 1.62 0.73 4.96
449 58163 Yerba Buena Island 37.80 -122.36 3.13 0.64 0.39 0.25 4.41 2.25 1.62 0.73
Table 2
Seq_no Sta_no Station Name Latitude Longitude Elevation Boore Borehole Borehole Refraction Distance
# Z(Vs=1.0) Z(Vs=1.5) Z(Vp=4.4) from Line
455 58262 Belmont - Envirotech 37.51 -122.30 0.15 3 0.012 0.55 1.99
1141 1720 Cupertino - Sunnyvale Rod & Gun 37.29 -122.08 0.22 157 0.008 0.27 0.95
406 47379 Gilroy Array #1 36.97 -121.57 192 0.003 0.010
464 58498 Hayward - BART Sta 37.67 -122.08 0.03 137 0.013 1.40 4.72
1155 1754 Hayward Fire - Station #1 37.67 -122.08 0.02 137 0.013 1.39 4.24
443 58130 SF - Diamond Heights 37.74 -122.43 0.14 178 0.008 2.04 4.95
1145 1739 Union City - Masonic Home 37.60 -122.00 0.07 168 0.013 2.91
Figure Captions
Figure 1. Bay Area velocity model and seismic refraction lines. The extent
of the Bay Area velocity model is indicated by the gray outline. The
seismic refraction lines are plotted as colored lines surrounded by cutouts.
The cutouts indicate the sections of the Brocher et al. (1997) model used
for comparison with the refraction results. The cross-sections plotted in
Figures 2 and 4-9 are indicated by the black bars and labeled with the
number of the Figure.
Figure 2. Comparison of S-wave velocities for the Los Gatos line. The
Brocher et al. (1997) model is plotted in solid colors, with color changes
indicating the Vs = 1.0, 1.5, and 2.5 km/s horizons. The refraction results
from Catchings et al. (2004) are shown as solid lines that are labeled. The
plot is masked where the ray coverage of the refraction inversion is too
sparse to resolve the velocity structure.
Figure 3. Vp/Vs from 38 shallow boreholes with S-wave layer velocities
in the range 0.9 < Vs < 1.3 km/s. The Vp and Vs estimates were derived
independently by Boore (2003): this range of Vs is appropriate for near-
surface rock layers. The straight line plotted on the graph shows the Vp/Vs
ratio used by Brocher et al. (1997) for average Cenozoic sediments.
Figure 4. Comparison of P-wave velocities for the Los Gatos line. The
Brocher et al. (1997) model is plotted in solid colors, with color changes
indicating the Vp = 2.4, 3.2, and 4.4 km/s horizons. The refraction results
from Catchings et al. (2004) are shown as solid lines that are labeled. The
plot is masked where the ray coverage of the refraction inversion is too
sparse to resolve the velocity structure.
Figure 5. Comparison of P-wave velocities for the Evergreen (east San
Jose) line. The representation of the models is the same as in Figure 4.
The fit of the Vp = 3.2 km/s horizon is excellent to the west of the
Evergreen basin, but poor to the east.
Figure 6. Comparison of P-wave velocities for the central section of the
East-Bay line. The representation of the models is the same as in Figure 4.
The fit of the Vp = 4.4 km/s horizon is adequate, while the Vp = 3.2 km/s
horizon (not plotted) is much shallower than the color change between the
green and orange colors.
Figure 7. Comparison of P-wave velocities for the San Pablo Bay section
of the East-Bay line. The representation of the models is the same as in
Figure 4. The masked area is underneath San Pablo Bay. The fit of the Vp
= 3.2 km/s horizon is excellent to the north of San Pablo Bay. The ~3 km
deep sedimentary basins inferred from the gravity on both sides of the bay
are not imaged by the seismic refraction.
Figure 8. Comparison of P-wave velocities for the eastern section of the
Cross-Bay line. The representation of the two models is the same as in
Figure 4. The eastern part of this line shows the Livermore basin, which
appears as a 4 km thick section of low velocity sediment. This is the only
refraction line that obtains slower velocities than the Brocher et al. (1997)
model. Even in the Livermore basin, however, the depth to the Vp = 3.2
km/s horizon obtained from the refraction is 1 km shallower than that
Inferred by Brocher et al. (1997).
Figure 9. Comparison of P-wave velocities for the western section of the
Cross-Bay line. The representation of the two models is the same as in
Figure 4. The refraction line does not see the velocity step across the San
Andreas fault incorporated by Brocher et al. (1997) into their model.
Figure 10. Comparison of the depths to the Vp = 3.2 km/s horizon from
the Brocher et al. (1997) model and the six refraction lines. The refraction
lines predominately sample three volumes of the Brocher 3D model, so the
depths from the Brocher model are clustered at 0.08, 0.70, and 1.60 km:
the large diamonds with error bars show the average ± one standard
deviation for each cluster. The line shows the regression of
zR
32.
on
zB
32.
used to correct the depths from the Brocher 3D model.
Bay Area
Refraction
Lines and 3D
Model Cutouts
Figure 1
2&4
5
6
7
8
9
0
0
5
0
0
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Depth (km)
Distance (km)
Los Gatos S-Wave Inversion (Catchings et al., 2004)
Brocher et al. (1997) 3D model in solid colors
Vs = 1.5 km/s
2.5 2.5
2.5
2.5
1.0
Figure 2
0
2.0
4.0
6.0
Depth (m)
0 5.0 10.0 15.0
Distance (km)
Los Gatos Inversion 1025 (Catchings et al., 2004)
Brocher et al. (1997) 3D model in solid colors
1500
2000
2000
2500
2500
3000
3000
3500
3500
4000
4000
4500
4500
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5500
5500
6000
6000
6500
6500
7000
7000
7500
7500
8000
8500
2.4
2.4
3.2
4.4
Vp = 4.4 km/s
Figure 4
0
1000
2000
3000
4000
5000
6000
Depth(m)
0 2000 4000 6000 8000 10000 12000 14000 16000 18000
Distance(m)
Sclow.a8 inversion 1018
1000
1500
2000
2500
00
3000
3000
3500
3500
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0 2000 4000 6000 8000 10000 12000 14000 16000 18000
0
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Depth (km)
0 5.0 10.0 15.0
Distance (km)
Evergreen Basin Inversion (Catchings et al., 2004)
Brocher et al. (1997) 3D model in solid colors
3.2 km/s
4.5
4.5
2.4
3.2
Figure 5
100000
4000
0 5.0 10.0 15.0
0
2.0
4.0
6.0
Depth (km)
Distance (km)
East Bay Inversion 23 (Central Section)
Brocher et al. (1997) 3D model in solid colors
Vp = 4.4 km/s
Figure 6
6000
0 5.0 10.0 15.0
0
2.0
4.0
6.0
Depth (km)
Distance (km)
East Bay Inversion 23 (San Pablo Bay)
Brocher et al. (1997) 3D model in solid colors
Vp = 4.4 km/s
3.2 3.2
4.4
2.4
2.4
Figure 7
3500
4500
5000
5500
60.0
0 5.0 10.0 15.0
0
2.0
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6.0
Depth (km)
Distance (km)
Cross-Bay Inversion 24 (East Section)
Brocher et al. (1997) 3D model in solid colors
Vp = 4.5 km/s
3.2 3.2
4.5
Figure 8
4000
4500
5000
6000
20.0
0 5.0 10.0 15.0
0
2.0
4.0
6.0
Depth (km)
Distance (km)
Cross-Bay Inversion 24 (West Section)
Brocher et al. (1997) 3D model in solid colors
Vp = 4.5 km/s
3.2
3.2
4.5
Figure 9
Appendix
P-Wave Velocity Structures for 6 Bay Area Refraction Lines
This Appendix locates the six refraction lines conducted by Catchings et al.
in 1991, 1993, 2000, and 2003. Four of these six lines were shot in 1991-93:
the Peninsula line, running from Hollister to Inverness, the East Bay line,
running from Hollister to Santa Rosa, the Cross Bay line, running from Ana
Nuevo to Livermore, and the Loma Prieta line. The last two lines were shot
in 2000 and 2003: the Los Gatos and Evergreen lines together run from Los
Gatos to Alum Rock Park, crossing the entire San Clara Valley.
The receiver locations and shot points for the 1991-93 lines are shown in
Figure A1, along with the receiver locations for the 2000 and 2003 lines. The
P-wave velocity structures obtained by tomographic inversion of these six
refraction lines are shown in Figures A2-A6. These refraction results are
presently being combined into a fence diagram that will be posted on the
Earthquake Team web-site at http://quake.usgs.gov.
5
10
15
20
Depth (km)
Distance (km)
Velocity (m/s)
2500
3500
4500
5500
6500
3500
4000
4000
4500
4500
5000
5000
5000
5500
5500
5500
5500
6000
6000
6500
6500
6500
7000
0
0 50 100 150 200
SF Peninsula Profile
Bay93p.at inversion 22
SE NW
Tres Pinos
Loma Prieta
Menlo Park
San Francisco
X-SAF
X-SAF
Marin Peninsula
Inverness
West Side of SAF
A A'
10
20
25
Depth (km)
Velocity (m/s)
2500
3500
4500
5500
6500
4000
4000
5000
5000
6000
6000
6000
0
5
0 50
Tres Pinos
(Tobias Ranch)
Soda Lake
Calaveras Fault
Crossing
Coyote Reservoir
Anderson Reservoir
Grant Co. Park
Monument Peak
Niles Cyn
Orinda/Gudde Ridge
Pinole Point
Upper San Leandro
Reservoir
Sears Point
San Pablo Bay
Annadel State Park
Santa Rosa
Soda Lake
100 150 200
Bay93e.e5 inversion 25
SE NW
B B'
6
Depth (km)
Velocity(m/s)
2500
3500
4500
5500
6500
3000
3500
3500
3500
4000
4000
4500
4500
5000
5000
5000
5000
5500
5500
5500
6000
6000
0
2
4
8
10
0 20
San Andreas Fault
Hayward Fault
40 60 80
Bay93xs.a1
inversion 24
San Gregorio Fault
Pacific Ocean
Livermore
San Francisco Bay
Santa Cruz Mtns
Coyote Hills
101
Calaveras Fault
Silver Creek Fault
Greenville Fault
SW NE
C C'
5
Depth(m)
Distance (km)
Velocity(m/s)
2000
3000
4000
5000
6000
2000
3000
4000
4000
5000
5000
5000
0
0 25
Bay93lp.b7 inversion 18
SW
Loma Prieta Mtn
San Andreas Fault
Sargent Fault
Calero Reservoir
Nasene Marks
Zayante Fault
Aptos
NE
4
5
6
0 5 10 15
Velocity (m/s)
2000
Sierra Rd.
Hayward
Fault
SJ Country
Club
McCollum
School
Shepard
School
I-680
I-280
King Road
Coleman
Avenue
Hester
School
10th
Street
101
Freeway
Lincoln
HS
3000
4000
5000
6000
1500
2000
2500
2500
3000
3000
3500
3500
4000
4000
4500
4500
5000
5000
5500
5500
6000
6000
6500
0 20
Sclowa.2 inversion 1010
Downtown
San Jose
Alum
Rock
Park NESW
2
3
Depth (km)
Depth (km)
Lglowa.1 inversion 93
2500
3000
3000
3500
3500
4000
4000
4500
4500
4500
5000
5000
5500
6000
0
0
1
5 10 15
Los Gatos
deepest part
of Jachen's
basin on line
Highway
Lexington
Dam
San
Andreas
Fault
Blossom
Hill Road
Campbell
McGlincy
Well
... [8] We have assembled an extensive active-source data set for the SFB region consisting of about 5,500 chemical explosions or air gun blasts (Figure 2a), including data that have never been utilized previously for seismic tomography. Traveltimes for controlled source experiments recorded by temporary seismic stations used in developing the tomography model include those from studies described by Warren [1978Warren [ , 1981, Mooney and Luetgert [1982], Walter and Mooney [1982], Blumling et al. [1985], Mooney and Colburn [1985], Meltzer et al. [1987], Murphy et al. [1992], Brocher and Moses [1993], Brocher and Pope [1994], Kohler and Catchings [1994], Li et al. [1997], Parsons and Zoback [1997], Williams et al. [1999], Boatwright et al. [2004], Brocher et al. [2004. We extracted catalog phase arrivals from the Northern California Earthquake Data Center (NCEDC) for the shots recorded at USGS network stations [Brocher, 2003]. ...
... The oval-shaped, NW-trending, Cupertino Basin, located along the western edge of the valley, is more than 4 km thick according to our model (Figures 3b, 3c, and 8). The tomography results are consistent with gravity anomalies ( Figure 5b) and seismic reflection profiles showing that the basin is asymmetric, thickening westward, and bounded to the west by range-front thrust faults including the Monte Vista fault [Langenheim et al., 1997a;Stanley et al., 2002;Boatwright et al., 2004;Williams et al., 2004]. Choosing the 4.5 km/s contour as the base of sedimentary deposits (basin thickness of 4 -5 km; Figures 4d and 8) is consistent with both forward models and inversions of the gravity data (Langenheim et al., 1997a(Langenheim et al., , 1997bStanley et al., 2002]. ...
... Jachens et al. [2002] propose that this basin, formed initially as a rightstepover in the Calaveras fault system, is bounded by the Silver Creek and Hayward-Calaveras faults, which are currently overthrusting the basin. Equating the 5.0 km/s isocontour as the base of the Cenozoic sedimentary deposits along a two-dimensional seismic tomography model for the basin [Boatwright et al., 2004] results in a maximum thickness of the Cenozoic deposits of about 3.3 km, at the lower end of basin estimates derived from gravity inversions (3-5 km, Jachens et al. [2002]; 5 km, Ponce et al. [2005]; 4-6 km, Stanley et al. [2005]). The estimates are reasonably consistent given that the corresponding Catchings et al. [2006] profile crosses the shallower part of the basin to the north, not the deeper part of the basin to the south. ...
Three-dimensional P wave velocity model for the San Francisco Bay region, California
Article
Full-text available
[1] A new three-dimensional P wave velocity model for the greater San Francisco Bay region has been derived using the double-difference seismic tomography method, using data from about 5,500 chemical explosions or air gun blasts and approximately 6,000 earthquakes. The model region covers 140 km NE-SW by 240 km NW-SE, extending from 20 km south of Monterey to Santa Rosa and reaching from the Pacific coast to the edge of the Great Valley. Our model provides the first regional view of a number of basement highs that are imaged in the uppermost few kilometers of the model, and images a number of velocity anomaly lows associated with known Mesozoic and Cenozoic basins in the study area. High velocity (Vp > 6.5 km/s) features at ∼15-km depth beneath part of the edge of the Great Valley and along the San Francisco peninsula are interpreted as ophiolite bodies. The relocated earthquakes provide a clear picture of the geometry of the major faults in the region, illuminating fault dips that are generally consistent with previous studies. Ninety-five percent of the earthquakes have depths between 2.3 and 15.2 km, and the corresponding seismic velocities at the hypocenters range from 4.8 km/s (presumably corresponding to Franciscan basement or Mesozoic sedimentary rocks of the Great Valley Sequence) to 6.8 km/s. The top of the seismogenic zone is thus largely controlled by basement depth, but the base of the seismogenic zone is not restricted to seismic velocities of ≤6.3 km/s in this region, as had been previously proposed.
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... To derive a relation below 50 m, I compiled VSP and sonic log data for the Franciscan Complex at various depths up to 2.7 km (Majer et al., 1988;Newhouse et al., 2004;Brocher, 2005b), laboratory measurements of Franciscan Complex rocks (Stewart and Peselnick, 1978), laboratory measurements for graywackes (Christensen and Mooney, 1995;Brocher and Christensen, 2001), and tomography velocities at various depths up to 20 km (Beaudoin et al., 1996;Parsons and Zoback, 1997;Hole et al., 2000;Boatwright et al., 2004;Haukkson et al., 2004;Hardebeck et al., 2004). These observations ( Figure 4A) were fit with a 5 th order polynomial: ...
... This average value plots about 0.5 km/s below the general trend in Figure 1.Equations 1 to 4 represent a significant departure from the relations used in the 1997 USGS Velocity Model for the Bay Area(Brocher et al., 1997). Based on equations 1 to 4, the Vs used in the sedimentary basins byBrocher et al. (1997) was too low (by a factor of 30% or more).Subsequent observations of compressional wave arrival times from local and teleseismic earthquakes in Santa Clara Valley indicate that that the geometry of the Cenozoic basins and the Vp used in the basins there(Brocher et al., 1997) are accurate(Fletcher et al., 2003).Fletcher et al. (2003) andBoatwright et al. (2004) note, however, that Vs used in this model within the basins are too small. Using equations 1 or 2 to calculate Vs from Vp in the velocity model ofBrocher et al. (1997) would substantially improve the accuracy of the 1997 model in these basins by increasing the model Vs in the basins. ...
Compressional and shear wave velocity versus depth in the San Francisco Bay Area, California: Rules for USGS Bay Area Velocity Model 05.0.0
Technical Report
Full-text available
  • Aug 2005
This report summarizes and documents empirical compressional wave velocity (Vp) versus depth relationships for several important rock types in northern California used in constructing the new USGS Bay Area Velocity Model 05.0.0 [http://www.sf06simulation.org/]. These rock types include the Jurassic and Cretaceous Franciscan Complex (metagraywacke and greenstones), serpentinites, Cretaceous Salinian and Sierra granites and granodiorites, Jurassic and Cretaceous Great Valley Sequence, and older Cenozoic sedimentary rocks (including the La Honda basin). Similar relations for less volumetrically important rocks are also developed for andesites, basalts, gabbros, and Sonoma Volcanics. For each rock type I summarize and plot the data used to develop the velocity versus depth relationships. These plots document the existing constraints on the proposed relationships. This report also presents a new empirical Vp versus depth relation derived from hundreds of measurements in USGS 30-m vertical seismic profiles (VSPs) for Holocene and Plio-Quaternary deposits in the San Francisco Bay area. For the upper 40 m (0.04 km) these mainly Holocene deposits, can be approximated by Vp (km/s) = 0.7 + 42.968z – 575.8z2 + 2931.6z3 – 3977.6z4, where z is depth in km. In addition, this report provides tables summarizing these VSP observations for the various types of Holocene and Plio-Quaternary deposits. In USGS Bay Area Velocity Model 05.0.0 these compressional wave velocity (Vp) versus depth relationships are converted to shear wave velocity (Vs) versus depth relationships using recently proposed empirical Vs versus Vp relations. Density is calculated from Vp using Gardner’s rule and relations for crystalline rocks proposed by Christensen and Mooney (1995). Vs is then used to calculate intrinsic attenuation coefficients for shear and compressional waves, Qs and Qp, respectively.
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... Regional velocity models are also available for some areas outside Japan, i.e., the 3D Community Velocity Model CVM-S4 (Kohler et al., 2003) and CVM-H1.1.0 (Süss and Shaw, 2003) for the Southern California, as well as the 3D Velocity Model of the Bay Area (Boatwright et al., 2004) for the Northern California. These regional velocity models are developed primarily to model the propagation of long-period ground motions (> ~1.0 s). ...
Which is a better proxy, site period or depth to bedrock, in modelling linear site response in addition to the average shear-wave velocity?
Article
Full-text available
This study aims to identify the best-performing site characterization proxy alternative and complementary to the conventional 30 m average shear-wave velocity VS30, as well as the optimal combination of proxies in characterizing linear site response. Investigated proxies include T0 (site fundamental period obtained from earthquake horizontal-to-vertical spectral ratios), VSz (measured average shear-wave velocities to depth z, z= 5, 10, 20 and 30 m), Z0.8 and Z1.0 (measured site depths to layers having shear-wave velocity 0.8 and 1.0 km/s, respectively), as well as Zx-infer (inferred site depths from a regional velocity model, x=0.8 and 1.0, 1.5 and 2.5 km/s). To evaluate the performance of a site proxy or a combination, a total of 1840 surface-borehole recordings is selected from KiK-net database. Site amplifications are derived using surface-to-borehole response-, Fourier- and cross-spectral ratio techniques and then are compared across approaches. Next, the efficacies of 7 single-proxies and 11 proxy-pairs are quantified based on the site-to-site standard deviation of amplification residuals of observation about prediction using the proxy or the pair. Our results show that T0 is the best-performing single-proxy among T0, Z0.8, Z1.0 and VSz. Meanwhile, T0 is also the best-performing proxy among T0, Z0.8, Z1.0 and Zx-infer complementary to VS30 in accounting for the residual amplification after VS30-correction. Besides, T0 alone can capture most of the site effects and should be utilized as the primary site indicator. Though (T0, VS30) is the best-performing proxy pair among (VS30, T0), (VS30, Z0.8), (VS30, Z1.0), (VS30, Zx-infer) and (T0, VSz), it is only slightly better than (T0, VS20). Considering both efficacy and engineering utility, the combination of T0 (primary) and VS20 (secondary) is recommended. Further study is needed to test the performances of various proxies on sites in deep sedimentary basins.
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... Most of these depth parameters were obtained from regional velocity structure models (Graves and Aagaard, 2011;Ancheta et al., 2014), that is, the Community Velocity Model-S4 (CVM-S4) (Magistrale et al., 2000) and CVM-H1.1.0 (Süss and Shaw, 2003) basin models for southern California, 3D velocity model of the bay area (Boatwright et al., 2004) for northern California, and the Japan Seismic Hazard Information Station (J-SHIS) model (Fujiwara et al., 2009) for Japan. ...
Testing the Depths to 1.0 and 2.5 km/s Velocity Isosurfaces in a Velocity Model for Japan and Implications for Ground‐Motion Modeling
Article
  • Aug 2019
In the Next Generation Attenuation (NGA-West2) project, a three-dimensional subsurface structure model (Japan Seismic Hazard Information Station, J-SHIS) was queried to establish depths to 1.0 and 2.5 km/s velocity isosurfaces for sites without depth measurement in Japan. In this paper, we evaluate the depth parameters in the J-SHIS velocity model by comparing them to their corresponding site-specific depth measurements derived from selected KiK-net velocity profiles. The comparison indicates that the J-SHIS model underestimates site depths at shallow sites and overestimates depths at deep sites. Similar issues were also identified in the Southern California Basin Model. Besides, our results also show that these under- and over-estimations have a potentially significant impact on ground-motion prediction using NGA-West2 ground motion models (GMMs). Site resonant period may be considered as an alternative to depth parameter in the site term of a GMM.
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... Other recent seismic investigations detected materials with low seismic ve locities beneath the Evergreen gravity low. A seismic refraction profile that in part followed the same path as the seismic reflection profile discussed above (Catchings et al., 2003;Boatwright et al., 2004) detected materials with low seismic velocities characteristic of Cenozoic basin fill to depths of at least 3 km below the center of the gravity low. Materials with much higher velocities were detected at considerably shallower depths both beneath the midvalley gravity ridge southwest of the gravity low and also to the northeast of the gravity low. ...
The Evergreen basin and the role of the Silver Creek fault in the San Andreas fault system, San Francisco Bay region, Californ
Article
The Evergreen basin is a 40-km-long, 8-km-wide Cenozoic sedimentary ¬basin that lies mostly concealed beneath the northeastern margin of the Santa Clara Valley near the south end of San Francisco Bay (California, USA). The basin is bounded on the northeast by the strike-slip Hayward fault and an approximately parallel subsurface fault that is structurally overlain by a set of west-verging reverse-oblique faults which form the present-day southeastward extension of the Hayward fault. It is bounded on the southwest by the Silver Creek fault, a largely dormant or abandoned fault that splays from the active southern Calaveras fault. We propose that the Evergreen ¬basin formed as a strike-slip pull-apart basin in the right step from the Silver Creek fault to the Hayward fault during a time when the Silver Creek fault served as a segment of the main route by which slip was transferred from the central California San Andreas fault to the Hayward and other East Bay faults. The dimensions and shape of the Evergreen basin, together with palinspastic reconstructions of geologic and geophysical features surrounding it, suggest that during its lifetime, the Silver Creek fault transferred a significant portion of the ∼100 km of total offset accommodated by the Hayward fault, and of the 175 km of total San Andreas system offset thought to have been accommodated by the entire East Bay fault system. As shown previously, at ca. 1.5–2.5 Ma the Hayward-Calaveras connection changed from a right-step, releasing regime to a left-step, restraining regime, with the consequent effective abandonment of the Silver Creek fault. This reorganization was, perhaps, preceded by development of the previously proposed basin-bisecting Mount Misery fault, a fault that directly linked the southern end of the Hayward fault with the southern Calaveras fault during extinction of pull-apart activity. Historic seismicity indicates that slip below a depth of 5 km is mostly transferred from the Calaveras fault to the Hayward fault across the Mission seismic trend northeast of the Evergreen basin, whereas slip above a depth of 5 km is transferred through a complex zone of oblique-reverse faults along and over the northeast basin margin. However, a prominent groundwater flow barrier and related land-subsidence discontinuity coincident with the concealed Silver Creek fault, a discontinuity in the pattern of seismicity on the Calaveras fault at the Silver Creek fault intersection, and a structural sag indicative of a negative flower structure in Quaternary sediments along the southwest basin margin indicate that the Silver Creek fault has had minor ongoing slip over the past few hundred thousand years. Two earthquakes with ∼M6 occurred in A.D. 1903 in the vicinity of the Silver Creek fault, but the available information is not sufficient to reliably identify them as Silver Creek fault events.
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... The geology of the central and northern CF, for which we provide refined slip distribution estimates, has not been precisely constrained, making evaluation of the factors responsible for the distribution of creeping and locked patches difficult. The sedimentary rocks of the Evergreen Basin, composed in great part of clays, overlaying Franciscan bedrock at 3-5 km depth [Koltermann and Gorelick, 1992;Wilson and Gorelick, 1996;Jachens et al., 2002;Williams et al., 2002;Boatwright et al., 2004;Ponce et al., 2005;Watt et al., 2007] could provide the conditions for creep on much of the shallow portion of the central CF [Sieh and Williams, 1990]. However, the limited creep on the northern CF despite the existence of similar deposits in the Livermore basin [California Department of Water Resources, 1980] may argue for a more complicated control on the slip behavior. ...
Interseismic coupling and refined earthquake potential on the Hayward-Calaveras fault zone
Article
Full-text available
  • Nov 2015
Interseismic strain accumulation and fault creep is usually estimated from GPS and alignment arrays data, which provide precise but spatially sparse measurements. Here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the Hayward and Calaveras Faults (HF and CF) in the East San Francisco Bay Area. The large 1992-2011 SAR data set permits evaluation of short- and long-wavelength deformation larger than 2 mm/yr without alignment of the velocity field to a GPS-based model. Our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along-fault surface creep rates. Creep rates vary from 0 ± 2 mm/yr on the northern CF to 14 ± 2 mm/yr on the central CF south of the HF surface junction. We estimate the long-term slip rates by inverting the long-wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field. This distribution of slip reveals the locations of locked and slowly creeping patches with potential for a M6.8 ± 0.3 on the HF near San Leandro, a M6.6 ± 0.2 on the northern CF near Dublin, a M6.5 ± 0.1 on the HF south of Fremont, and a M6.2 ± 0.2 on the central CF near Morgan Hill. With cascading multisegment ruptures the HF rupturing from Berkeley to the CF junction could produce a M6.9 ± 0.1, the northern CF a M6.6 ± 0.1, the central CF a M6.9 ± 0.2 from the junction to Gilroy, and a joint rupture of the HF and central CF could produce a M7.1 ± 0.1.
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... For the San Francisco Bay Area (SFBA), we use Version 08.3.0 of a 3D Bay Area velocity model developed by Boatwright et al. (2004; http://earthquake.usgs.gov/research/ structure/3dgeologic/). ...
NGA-West2 site database
Article
Full-text available
The NGA-West2 site database (SDB) contains information on site condition and instrument housing for 4,147 strong-motion stations with recordings in the project flatfile. The stations are from active tectonic regions, mainly in California, Japan, Taiwan, China, and the Mediterranean area. The principal site parameter is the time-averaged shear wave velocity in the upper 30 m (V S30), which we characterize using measurements where available (2,013 sta-tions) and proxy-based relationships otherwise. We also provide basin depths from published models for 2,761 sites mostly in California and Japan. We improved the documentation and consistency of site descriptors used as proxies for V S30 estimation (surface geology, ground slope, and geotechnical or geo-morphic categories) and analyzed proxy performance relative to V S30 values from measurements. We present protocols for V S30 estimation from proxies that emphasize methods minimizing bias and dispersion relative to data. For each site, we provide the preferred V S30 and its dispersion.
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... However, it is a slight improvement over prior tomography models, such as the Hole et al. (2000) model, which exhibits a velocity of ϳ4 km/sec at 1 km depth in the Livermore basin and up to ϳ5.5 km/sec in other parts of the model region. Although travel-time tomography can image the basin at depth, which may help constrain possible focusing effects, additional information about near-surface conditions from boreholes, active-source seismic experiments (e.g., Walter and Mooney, 1982;Catchings et al., 2004;Boatwright et al., 2004), and geotechnical studies is necessary to fully understand how this basin may amplify shaking from a large earthquake. ...
Seismic Velocity Structure and Seismotectonics of the Eastern San Francisco Bay Region, California
Article
Full-text available
  • Jun 2007
The Hayward Fault System is considered the most likely fault system in the San Francisco Bay Area, California, to produce a major earthquake in the next 30 years. To better understand this fault system, we use microseismicity to study its structure and kinematics. We present a new 3D seismic-velocity model for the eastern San Francisco Bay region, using microseismicity and controlled sources, which re- veals a 10% velocity contrast across the Hayward fault in the upper 10 km, with higher velocity in the Franciscan Complex to the west relative to the Great Valley Sequence to the east. This contrast is imaged more sharply in our localized model than in previous regional-scale models. Thick Cenozoic sedimentary basins, such as the Livermore basin, which may experience particularly strong shaking during an earthquake, are imaged in the model. The accurate earthquake locations and focal mechanisms obtained by using the D model allow us to study fault complexity and its implications for seismic hazard. The relocated hypocenters along the Hayward Fault in general are consistent with a near-vertical or steeply east-dipping fault zone. The southern Hayward fault merges smoothly with the Calaveras fault at depth, suggesting that large earthquakes may rupture across both faults. The use of the 3D velocity model reveals that most earth- quakes along the Hayward fault have near-vertical strike-slip focal mechanisms, con- sistent with the large-scale orientation and sense of slip of the fault, with no evidence for zones of complex fracturing acting as barriers to earthquake rupture.
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... Other recent seismic investigations detected materials with low seismic ve­ locities beneath the Evergreen gravity low. A seismic refraction profile that in part followed the same path as the seismic reflection profile discussed above (Catchings et al., 2003;Boatwright et al., 2004) detected materials with low seismic velocities characteristic of Cenozoic basin fill to depths of at least 3 km below the center of the gravity low. Materials with much higher velocities were detected at considerably shallower depths both beneath the mid­valley gravity ridge southwest of the gravity low and also to the northeast of the gravity low. ...
Definition of the Silver Creek Fault and Evergreen Basin Sediments From Seismic Reflection Data, San Jose, California
Article
Full-text available
  • Dec 2002
Preliminary interpretation of 20 km of P-wave seismic reflection data provides new information on the configuration of the basement surface, the nature of the sedimentary basin fill and the location of the Silver Creek Fault (SCF) adjacent to and within the elongate, northwest-trending Evergreen Basin (EB), located in San Jose, California. These data, which were acquired as part of a larger project to understand seismic hazards in the Santa Clara Valley, were focused on determining fault locations, basin shape, and seismic velocity structure that could effect earthquake ground motions. The 40-km long by 8-km wide EB has been defined previously by gravity modeling and seismic tomography. We acquired two seismic profiles using a 240-channel recording system with 5-m receiver and 10-m source intervals. Profile 1, which follows the Guadalupe River northwestward just west of the western edge of the EB, reveals a moderately undulating basement surface overlain by about 400 m of well-layered Pleistocene and possibly Pliocene sedimentary deposits. Basement paleotopography is indicated by undulations of up to 50 m of relief over about 200 m lateral distance, with overlying beds truncated against the basement highs. Profile 2 trends northeastward and crosses the EB. A 2-km-long, and as deep as 450-m basement reflection on the western end of this profile shows 100 m of local relief and dips gently eastward before appearing to terminate abruptly in the vicinity of the previously inferred trace of the SCF. A steep gravity gradient and a groundwater boundary inferred from InSAR are the only previous constraints on the location of the SCF here as the fault has no instrumentally-recorded seismicity. We interpret this basement reflection termination to be the location of the SCF. To the east, the sedimentary fill appears to thicken abruptly as indicated by the generally flat-lying layered reflections extending to at least 1.5 km depth. The SCF dip is poorly constrained but appears to dip steeply to the east, as indicated by the series of westward terminations of reflections just east of the fault. Bedding in a 500-m wide zone above the easternmost basement reflection is tilted and deformed, relative to reflections outside the SCF zone, but the presence of faulting is unclear. The trace of the InSAR boundary directly overlies the eastern tip of the basement reflection termination, and it also overlies the zone of more concentrated deformation, but it is not clearly associated with faulted near-surface sediments at this preliminary stage of analysis.
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Deformation from the 1989 Loma Prieta earthquake near the southwest margin of the Santa Clara Valley, California
Article
Damage to pavement and near-surface utility pipes caused by the 17 October 1989 Loma Prieta earthquake provides evidence for ground deformation in a 663 km2 area near the southwest margin of the Santa Clara Valley, California (USA). A total of 1427 damage sites, collected from more than 30 sources, are concentrated in four zones, three of which are near previously mapped faults. In one of these zones, the channel lining of Los Gatos Creek, a 2-km-long concrete strip trending perpendicular to regional geologic structure, was broken by thrusts that were concentrated in two belts, each several tens of meters wide, separated by more than 300 m of relatively undeformed concrete. To gain additional measurement of any permanent ground deformation that accompanied this damage, we compiled and conducted post-earthquake surveys along two 5 km lines of horizontal control and a 15 km level line. Measurements of horizontal distortion indicate ~0.1 m shortening in a northeastsouthwest direction across the valley margin, similar to the amount measured in the channel lining. Evaluation of precise leveling by the National Geodetic Survey showed a downwarp with an amplitude of >0.1 m over a span of >12 km that resembled regional geodetic models of coseismic deformation. Although the leveling indicates broad, regional warping, abrupt discontinuities characteristic of faulting characterize both the broad-scale distribution of damage and the local deformation of the channel lining. Reverse movement, largely along preexisting faults and probably enhanced significantly by warping combined with enhanced ground shaking, produced the documented coseismic ground deformation.
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P-and S-Velocities from Surface-to-Borehole Logging
  • Jan 2003
  • D M Boore
  • T M Brocher
  • E E Brabb
  • R D Catchings
  • G S Fuis
  • T E Fumal
Boore, D.M., (2003). P-and S-Velocities from Surface-to-Borehole Logging, http://quake.wr.usgs.gov/~boore/data_online.htm. Brocher, T.M., E.E. Brabb, R.D. Catchings, G.S. Fuis, T.E. Fumal, R.C.
A crustal-scale 3-D seismic velocity model for the
  • Jan 1997
  • 435-436
  • A S Jachens
  • R E Jayko
  • R J Kayen
  • Tom Mclaughlin
  • M J Parsons
  • R G Rymer
  • C M Stanley
  • Wentworth
Jachens, A.S. Jayko, R.E. Kayen, R.J. McLaughlin, Tom Parsons, M.J. Rymer, R.G. Stanley, C.M. Wentworth, (1997). A crustal-scale 3-D seismic velocity model for the San Francisco Bay area, California, Eos, vol.78, no.46, Suppl., pp.435-436.
The effects of site characteristics on near-source recordings of strong-ground motion A workshop on site-specific effects of soil and rock on ground motion and the implications for earthquake-resistant design
  • Jan 1983
  • 83-0845
  • Campbell
  • Kenneth
Campbell, Kenneth W, (1983). The effects of site characteristics on near-source recordings of strong-ground motion. Hays, Walter W. (ed.), Kitzmiller, Carla, and Darnell, Diana, A workshop on site-specific effects of soil and rock on ground motion and the implications for earthquake-resistant design, Open-file Report 83-0845.
Basin structure and velocities from the 2000 Santa Clara Seismic Investigation (SCSI) as related to earthquake hazards and water resources
  • Jan 2004
  • R D Catchings
  • G Gandhok
  • M R Goldman
  • R Hansen
  • R Mclaughlin
Catchings, R.D., G. Gandhok, M.R. Goldman, R. Hansen, and R. McLaughlin (2004). Basin structure and velocities from the 2000 Santa Clara Seismic Investigation (SCSI) as related to earthquake hazards and water resources, western Santa Clara Valley, California, U.S. Geological Survey Open-File Report 04-xxx.
Compilation of 71 additional sonic and density logs from 59 oil test wells in the San Francisco Bay area
  • Jan 1998
  • 98-615
  • C A Tiballi
  • T M Brocher
Tiballi, C.A., and T.M. Brocher (1998). Compilation of 71 additional sonic and density logs from 59 oil test wells in the San Francisco Bay area, U.S. Geological Survey Open-File Report 98-615, 131 p.