Group B, Poster #092, Earthquake Geology
A New 3D Fault Model of the Southern San Joaquin Fold and Thrust Belt, California, and its implications for Regional Earthquake Hazards
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Poster Presentation
2024 SCEC Annual Meeting, Poster #092, SCEC Contribution #13651 VIEW PDF
3D model of the structures in the region, including fault segments along strike from the 1980s earthquake sequences (Kettleman Middle and South Domes, Lost Hills) and within the Temblor Range. This model is based on analysis of industry seismic data depth-converted using the SCEC Community Velocity Model and coupled with horizon picks from CalGEM Oil and Gas Well Data, Cal DWR groundwater wells, CPT data, as well as a relocated seismicity catalog and focal mechanism solutions. To constrain activity in the Pleistocene and Holocene section, we leverage our near-surface well data and portions of our seismic data. Our model reveals that along strike, the system changes from a structural wedge to a composite growth fault-bend fold. Additionally, where the structural styles change along strike, we observe distinct variations in the easternmost extent of deformation in the basin. Specifically, those segments characterized by fault-bend folding send slip into the basin on an upper detachment, which is manifest in both detachment folds and additional thrust ramps that have been active through the Late Pleistocene. At depth, these fault segments sole to two major basal detachment levels that extend west beneath the Temblor Ranges. Folding of Pleistocene strata along axial surfaces that define the transition from ramps to detachments suggests that past earthquakes were not limited to the fault segments that ruptured in the 1980s but rather may have involved detachments and other thrust ramps in the Temblor Range and San Joaquin basin. Such multi-segment/multi-fault events in the broader San Joaquin Fold and Thrust Belt would pose considerable seismic hazards.
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