Complete Bouguer anomaly map of the Livermore Valley area, California

Holden, K.D.

doi:10.3133/ofr76761

Cited by 3 publications

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“…This sequence is thought to be underlain by the Franciscan Complex but basement has not yet been penetrated there [ Brocher , 2005a]. The rhomboidal geometry of the basin in map view at 3 km depth (Figure 3b) closely resembles the shape of the pronounced gravity anomaly low over the basin [Figure 5b; Holden , 1976; Brocher , 2005a]. Velocity depth curves for the Bay Area [ Brocher , 2005b] indicate that at 6 km depth, the contrast between the sedimentary strata and basement is relatively weak, making the top of the basement difficult to image using tomography.…”

Section: Model Resultsmentioning

confidence: 99%

Three‐dimensional P wave velocity model for the San Francisco Bay region, California

et al. 2007

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[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 (V p > 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.Citation: Thurber, C. H., T. M. Brocher, H. Zhang, and V. E. Langenheim (2007), Three-dimensional P wave velocity model for the San Francisco Bay region, California,

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