EAR-PF: Adjoint Tomography, Seismic Hazard, and Active Tectonics of the San Joaquin Basin, California

Tape Carl H, Pasadena CA

Investigators

Abstract

Dr. Carl Tape is awarded an NSF Earth Science Postdoctoral Fellowship to carry out a program of research and education at Harvard University. He will construct a three-dimensional structure model of the San Joaquin basin and adjacent regions. The basin will be described in terms of seismic velocity variations, density variations, and geometries of the major geologic interfaces, such as basin boundaries and faults. The investigation will consist of three stages. First, a basin model will be constructed using industry well logs and seismic reflection data. Second, numerical simulations of previously recorded earthquakes in the region will be performed using supercomputing clusters. Third, the basin model will be iteratively improved using the results of the numerical simulations in a procedure known as adjoint tomography. The resultant three-dimensional structure will be interpreted in the context of the local active tectonics, such as the delamination of the adjacent Sierra Nevada. Results from the earthquake simulations will be used to assess the seismic hazard in the San Joaquin basin. The Great Valley lies west of the Sierra Nevada and east of the Coast Ranges. It is the largest agricultural producer in the United States, a major oil producer, and home to more than 6.5 million people. The southern portion of the valley, the San Joaquin basin, is filled with several kilometers of sediment that makes the valley prone to enhanced and prolonged shaking during earthquakes. The region is surrounded by active faults, including the San Andreas fault to the west and the White Wolf and Garlock faults to the south. The basin is one of the most prominent tectonic features in southern California, yet its structure and seismic response are not well known. The findings of both the seismic hazard and the active tectonics will be conveyed to the communities of the San Joaquin basin, with emphasis on Bakersfield, which has the largest population and greatest seismic risk.