← Back to Sessions

Signatures of Seismic Waveguides in Los Angeles From Numerical Simulations and Noise Cross Correlations

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

Waveguides are confined geological units capable of channeling and focusing seismic energy over long distances. In the Los Angeles (LA) area, 3D simulations (e.g., TeraShake, ShakeOut) suggest that the presence of such waveguides caused by the connectivity of the sedimentary basins (Los Angeles - San Gabriel – Chino – San Bernardino) strongly increases ground motion predictions for large, northwestward ruptures on the southern San Andreas fault (SAF). However, the efficiency in focusing and increase in ground motions due to the waveguides depend on the accuracy of the basin structure in the velocity models.

In this project, we attempt to validate the presence of several waveguides in the LA region, as indicated by 3D earthquake simulations, with observed data from earthquakes and ambient noise. Using over 700 temporary (nodal and broadband) and permanent (SCSN) stations as receivers, and 14 station sources located along the SAF as virtual sources, we calculate and compare all 9 components of the correlation and Green’s function tensor. We calculate over ~40,000 correlations. We compare the numerical and empirical surface-to-surface Green tensors for small earthquakes that are located nearby stations, and for virtual sources located on the SAF. The regions of large peak motions caused by waveguide focusing in the simulations show generally good agreement with increases in the Green tensor amplitudes, supporting the presence of two separate waveguides in greater LA. Analysis of the cross terms and particle motions confirm that 0.1-0.5 Hz (2-10s) surface waves play the most important role in the waveguide focusing.

Presenting Author: Nan Wang

Student Presenter: Yes

Authors