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Mapping the 3D Structure of the San Gabriel and San Bernardino Basins, Greater Los Angeles Area From Seismic and Gravity Measurements

The Basin Amplification Seismic Investigation (BASIN) project focuses on improving the seismic velocity model of the San Gabriel and San Bernardino basins. In the event of the anticipated magnitude 7.8 San Andreas fault earthquake rupture, these northern basins are thought to amplify propagating seismic waves and channel them towards the densely populated Los Angeles area. To investigate this amplification effect and improve ground shaking models, a better understanding of the subsurface structure of these basins is necessary. Here, we incorporate gravity data and receiver function interpretations, along the 10 seismic profiles of the project, to map the 3-dimensional structure of the San Gabriel and San Bernardino basins. The travel time to the sediment-basement interface obtained from P-to-S receiver functions was combined with Bouguer gravity data to determine the basin depth along the seismic profiles. We then extrapolated the 2D results to a complete 3D structure of the basins using the residual Bouguer gravity anomaly as a constraint. The basement interface shows a variable structure, with the deepest part of the basins near the San Jacinto fault on the southeastern side of the San Bernardino basin. In the western San Gabriel basin, the gravity data show a sharp increase near the active Raymond fault. Modeling of this abrupt change in the residual gravity anomaly aided the identification of a possible fault-related offset in the sediment-basement interface in one of our N-S trending receiver function profiles. Thus, the inclusion of gravity data with seismic measurements aids in identifying subsurface interfaces and can delineate subtle faults.

Presenting Author: Valeria Villa

Student Presenter: Yes

Day: 4/21/2021

Time: 9:45 AM - 11:00 AM Pacific

Additional Authors