Group B, Poster #008, Seismology

Internal Structure of Southern San Andreas Fault Zone from Traffic Signals recorded by a Dense Seismic Array

Hao Zhang, Haoran Meng, & Yehuda Ben-Zion
Poster Image: 

Poster Presentation

2022 SCEC Annual Meeting, Poster #008, SCEC Contribution #12000 VIEW PDF
We derive detailed properties of the shallow seismic structure across the southern San Andreas fault zone (SoSAFZ) in the Coachella Valley, using signals generated by freight trains and trucks and recorded by a dense nodal array near the Thousand Palms Oasis Preserve. The array consisted of a 4-km-long linear section with over 150 nodes and two 2-D subarrays with over 100 nodes each centered on the Banning Fault (BF) and Mission Creek Fault (MCF) strands of the SoSAFZ. Particle motion analyses indicate that the moving freight trains and trucks can be approximated by point sources that generate primarily Rayleigh waves. To model the movement of the trains and trucks, we back-project the Rayle...igh wave propagation in the two 2-D subarrays to the railway using the vertical component waveforms in a series of moving windows. We then stably measure the Rayleigh wave velocity according to the delay time and wave propagation direction for each neighboring station pair by averaging through multiple time windows. The results indicate a low-velocity zone around BF and a velocity reduction of over 45% across MCF towards the northeast. We further resolve about 10% density reduction using the amplitude ratio as well as incident and refracted angles across the bi-material interface at MCF. By employing the resolved Rayleigh wave velocity, we further model the amplitude decay and estimate the attenuation structure across the linear array. The derived Q-values show strong attenuation around the two fault strands as well as in the sediments of a local riverbed.