Seismic Structure Beneath Los Angeles From the BASIN Experiment

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications
Type: Oral
Date: 4/28/2020
Time: 08:30 AM
Room: 110 + 140
Description: 

The Basin Amplification Seismic INvestigation (BASIN) project is a multicomponent earthquake hazard project between LSU, Caltech, Harvard, Cal Poly Pomona and SDSU that focuses on characterizing the amplification of seismic waves as they travel through sedimentary basins. Our goal is to first map the structure of the San Gabriel and San Bernardino basins that are known to amplify seismic waves in the Los Angeles area and to integrate the basins’ structure into computer simulations of ground motion. As part of the BASIN project, we have deployed 744 nodal seismometers along 10 densely-spaced seismic profiles in the greater Los Angeles area starting in 2017. We launched the fourth and final phase of the BASIN seismic deployments in November 2019 with 262 nodes installed. These surveys are a new type of rapid, low-cost deployment that might be called urban seismology in which the nodes are mostly installed by volunteers who obtain direct approval from Los Angeles residents.

The 3-component data from the BASIN surveys along with other data sets are being used to construct a detailed 3D seismic velocity model toward the goal of better predicting strong ground motions in greater Los Angeles from events on the San Andreas fault. We will present results on the following components of the BASIN project. Receiver functions are used to map the Moho discontinuity, the sediment–basement interface, intermediary sedimentary layers and to identify possible fault offsets. Ambient noise spectral ratio measurements help constrain amplification and the depth to shallow interfaces with large impedance contrasts. Ambient noise correlations with the node stations and nearby SCSN stations produce Rayleigh and Love waves that are used to determine the shear wave speed structure as well as local and long-range amplification effects in the basin. Finally, we will compare our velocity models and empirical ground motion estimates to the Southern California Earthquake Center Community Velocity Models (CVMs) and resulting ground motion estimates, respectively.

Presenting Author: Patricia Persaud

Authors