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Simulated Ground Motion in Santa Clara Valley, California, and Vicinity from M6.7 Scenario Earthquakes

U.S. Geological Survey, Denver Federal Center, Box 25046, MS 966, Denver, Colorado 80225

Pengcheng Liu

U.S. Bureau of Reclamation, Denver Federal Center, Box 25007, MS 86-68330, Denver, Colorado 80225-0007

View larger version (102K): [in this window] [in a new window]   Figure 1. Regional map with two study areas shown as blue and red rectangles. The blue rectangle region was used for many San Andreas sources, and the red rectangle region was used for east bay sources. Probability of an M 6.5 or greater earthquake in a 30-yr period is shown color coded. City abbreviations are Berkeley, Brk; Fremont, Fr; Menlo Park, MP; Oakland, Oak; San Jose, SJ; and San Leandro, SL. Fault traces are gray. Fault abbreviations are Calaveras fault, north segment, Cal N; Calaveras, central segment, Cal C; Great Valley blind thrust, GVBT; Monterey Bay–Tularcitos faults, MB–T; Mount Diablo thrust, MtD; Monte Vista/Shannon fault system, MV/S; Hayward fault, south segment, S Hay; San Andreas fault, Peninsula segment, SAF; San Gregorio fault, SG; and Zayante–Vergeles fault system, ZV. Epicenters for M 6 or greater historical earthquakes are shown (open circles).

View larger version (121K): [in this window] [in a new window]   Figure 2. (a) Shear-wave velocity at a depth of 50 m below the model surface (70 m below the Earth’s surface), for model V12m of the CenCal geologic model. Shoreline is blue. The mapped region corresponds to the red rectangle of Fig. 1. The geographic coordinates of the southwest corner of the region are 121.6763° W longitude, 36.8390° N latitude, 10 km southeast of Watsonville, California. Gray lines correspond to surface traces of major faults. Open circles correspond to subsources on the Calaveras fault for some multisegment source-scenario simulations. Strong-motion stations in Milpitas (MIL) and at San Jose interchange (SJI) are over the Evergreen Basin (EV); San Francisco State University (SFSU) is at the edge of the Merced Basin (MB). Stations G1 and G2 (in the Gilroy Array), CAL (Calaveras Reservoir), CLD (Coyote Lake Dam), and SFO (San Francisco Airport) are also labeled. Other basins are labeled, including San Leandro Basin (SLB). (b) Shear-wave velocity for the V12m rendering of the CenCal geologic model at a depth of 750 m with locations of strong-motion stations (inverted triangles) and sources on two segments of the Calaveras fault, CN (northern) and CC (central) (open circles). The boundary of these segments occurs under the Calaveras reservoir (station CAL). See caption for Figure 2a for additional details.

View larger version (67K): [in this window] [in a new window]   Figure 3. M 7.2 source on the Peninsula segment of the SAF showing slip (top frame), subsource rise time (middle frame), and rupture front arrival time (bottom frame). The hypocenter is at 16-km depth. Rough lateral edges result from projecting a dipping variable-strike fault onto a vertical plane.

View larger version (39K): [in this window] [in a new window]   Figure 4. (a) Vp and Vs profiles for the shallow fill of the Evergreen (top) and Cupertino (bottom) Basins. Black curves are the USGS Bay Area Velocity Model 05.1.0 Tertiary basin fill; blue curves are the USGS Bay Area Velocity Model 05.1.0 Quaternary; red curves are the V12 Quaternary/Tertiary basin fill; green curves are the V9 Quaternary/Tertiary basin fill. Where not visible, green curves coincide with red curves. (b) Shallow detail of Vp and Vs profiles for the basin fill of the Evergreen (top) and Cupertino (bottom) Basins. Details are the same as for part (a) of this figure.

View larger version (51K): [in this window] [in a new window]   Figure 5. PHV (m/sec) for an M 6.8 Calaveras CN earthquake simulation with Danville epicenter (scenario 1). V12m velocity model is used. The white H indicates the epicenter. See Table 2 for further details. In this figure and the following PHV plots, the major faults are shown in black and the fault segment that ruptured is shown in red.

View larger version (49K): [in this window] [in a new window]   Figure 6. PHV (m/sec) for an M 6.8 southeast-to-northwest Calaveras CN scenario that begins under the Calaveras reservoir (white H) (scenario 2). V12m velocity model is used.

View larger version (81K): [in this window] [in a new window]   Figure 7. (a) PHV (m/sec) for an M 6.9 Calaveras CN+CC rupture scenario with epicenter (white H) near Danville (scenario 3). Rupture extends to within 2 km of the bottom of the figure. V12m velocity model is used. (b) Strong motion at station SJI compared for two Calaveras scenario earthquakes (scenarios 1 and 3). Darker traces correspond to an M 6.9 event.

View larger version (55K): [in this window] [in a new window]   Figure 8. PHV (m/sec) for an M 7.4 Calaveras fault scenario with epicenter (black H) near Coyote Lake and predominantly northwest rupture (scenario 6). V12m velocity model is used.

View larger version (43K): [in this window] [in a new window]   Figure 9. PHV (m/sec) for a South Hayward M 6.7 scenario with a Calaveras reservoir epicenter (white H) (scenario 7). V12m velocity model is used.

View larger version (44K): [in this window] [in a new window]   Figure 10. PHV (m/sec) for a South Hayward M 6.7 rupture (scenario 8). Rupture was moved about 2 km northwest compared to that of Figure 9. V12m velocity model is used.

View larger version (48K): [in this window] [in a new window]   Figure 11. PHV (m/sec) for an M 6.7 South Hayward fault scenario with an epicenter near Oakland (white H; scenario 9). The maximum PHV occurs in the Evergreen Basin. V12m velocity model is used.

View larger version (50K): [in this window] [in a new window]   Figure 12. PHV (m/sec) for a bilateral rupture on the South Hayward fault, M 6.7 (scenario 10). V12m velocity model is used.

View larger version (84K): [in this window] [in a new window]   Figure 13. (a) PHV (m/sec) for a South Hayward M 6.9 scenario with northwest-to-southeast rupture propagation (scenario 11). V9 velocity model is used. (b) South Hayward scenario-event seismograms (scenario 11). Top three traces are for station MIL, and bottom three traces are for station SJI. (c) Comparison of N45°W coda at San Jose interchange (SJI) for an M 6.9 South Hayward source using V9 and V12 velocity models (scenarios 11 and 12); V9-based seismogram is red, and V12-based seismogram is black.

View larger version (40K): [in this window] [in a new window]   Figure 14. PHV (m/sec) for a Monte Vista/Shannon M 6.7 simulation with northwest epicenter (black H) (scenario 13). V9 velocity model is used.

View larger version (40K): [in this window] [in a new window]   Figure 15. PHV (m/sec) corresponding to a Monte Vista/Shannon M 6.7 simulation with southeast epicenter (black H) (scenario 14). V12m velocity model is used.

View larger version (43K): [in this window] [in a new window]   Figure 16. PHV (m/sec) corresponding to a northwest-to-southeast rupture of an M 7.2 Peninsula SAF source (scenario 15). V12m velocity model is used.

View larger version (47K): [in this window] [in a new window]   Figure 17. PHV (m/sec) for an M 7.2 Peninsula SAF scenario with offshore hypocenter (black H) (scenario 16). V9 velocity model is used.

View larger version (50K): [in this window] [in a new window]   Figure 18. PHV (m/sec) for an M 7.2 Peninsula source with shallower slip than in Figure 17 but with most other source parameters the same (scenario 17). V9 velocity model is used.

View larger version (42K): [in this window] [in a new window]   Figure 19. PHV (m/sec) for an M 7.2 Peninsula SAF source with southeast-to-northwest rupture (scenario 20). V9 velocity model is used.

View larger version (15K): [in this window] [in a new window]   Figure A1. Shear-wave profile for La Honda Basin at a hypothetical site 200 m above sea level. The solid curve corresponds to the USGS Bay Area Velocity Model 05.1.0 at a location where the basin bottom contacts Salinian rock at 5 km below the surface. The two dashed curves represent approximate models. Homogeneous media (granitics with Vs=3.64 km/sec and ) are assumed to comprise the half-space for the nrattle computations.

View larger version (17K): [in this window] [in a new window]   Figure A2. Transfer functions for the three velocity profiles of Figure A1. The solid curve corresponds to the true model, the dashed curve corresponds to the preferred approximation, and the dotted-dashed curve corresponds to a simple approximation where the topography is removed without further corrections. Note that for frequencies greater than 0.4 Hz, the simple approach is 20% low on average, and continues to degrade with increasing frequency. While there is an unavoidable shift of subharmonics, the overall amplitude response of the preferred approximation is reasonably good.