Lithostratigraphic, borehole-geophysical, hydrogeologic, and hydrochemical data from the East Bay Plain, Alameda County, California

Sneed, Michelle; Orlando, Patricia v.P.; Borchers, James W.; Everett, Rhett R.; Solt, Michael; McGann, Mary; Lowers, Heather A.; Mahan, Shannon A.

doi:10.3133/ds890

Cited by 1 publication

(1 citation statement)

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“…The PGV values in Figure 1 show a pattern of high amplitudes around this feature and low values within it. The San Leandro basin (Brocher, 2005b;Sneed et al, 2015) is a sedimentary structure of moderate depth (1.5 km) spanning the San Francisco Bay shoreline for about 20 km northwest-southeast. This feature shows high PGV values, particularly for the case in Figure 1a.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Fault Geometry and Minimum Shear Wavespeed on 3D Ground-Motion Simulations for an Mw 6.5 Hayward Fault Scenario Earthquake, San Francisco Bay Area, Northern California

Rodgers

Pitarka

McCallen

2019

Bulletin of the Seismological Society of America

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We investigated the effects of fault geometry and assumed minimum shear wavespeed (VSmin) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (Mw) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming VSmin values of 500 and 250 m/s reveal that PGVs are on average 25% higher west of the HF when using the lower VSmin, with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two VSmin cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower VSmin west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or VSmin of 250 m/s. We conclude that assuming a VSmin of 500 m/s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth <10 km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.

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Section: Introductionmentioning

confidence: 99%