Analysis of the Basin Amplification Seismic Investigation (BASIN) project in Los Angeles, California

Abstract:

In this presentation, we summarize the results of several studies using data recorded as part of the BASIN seismic survey carried out in 2017-19 in the greater Los Angeles, California area. This experiment involves dense node arrays deployed across the San Gabriel (SG) and San Bernardino (SB) Basins on the northern edge of Los Angeles. The motivation for the study is that the SG and SB basins act as a waveguide that channels energy from the S. San Andreas Fault into downtown Los Angeles. The shear wave velocities and location of the basement interface contribute to understanding the channel structure, and hence its contribution to the seismic hazard of Los Angeles.

We use ambient noise correlations between the nodes and between the nearby Southern California Seismic Network (SCSN) broadband stations, to map the shear wave velocity in the top 2 km. Key to obtaining the necessary depth resolution is the correct mode identification of the surface waves (SW). The correlations are also used to image SW-SW scattering (reflections) to map faults and discontinuities.

Receiver functions and autocorrelations along the 10 profiles are used to determine the depth of basement and Moho. We then use gravity measurements to extend the profiles to a full mesh of basement depths that span the SG and SB basins. Gravity also helps to resolve the interface identification in the receiver function profiles. The basement-sediment mesh and the enclosed shear-wave velocities are main components of the model for the SG and SB basins.