Evidence for faulting and fluid-driven earthquake processes from seismic attenuation variations beneath Los Angeles

Chiara Nardoni, & Patricia Persaud

Under Review April 6, 2024, SCEC Contribution #13447

Seismicity in the Los Angeles metropolitan area has been primarily attributed to the regional stress loading. Below the urban areas, earthquake sequences have occurred over time showing migration off the faults and providing evidence that secondary processes may be involved in their evolution. Combining high-frequency seismic attenuation with other geophysical observations is a powerful tool for understanding which Earth properties distinguish regions with ongoing seismicity. We develop the first high-resolution 3D seismic attenuation models across the region east of downtown Los Angeles using 5,300 three-component seismograms from local earthquakes recorded by a dense seismic array. We present frequency-dependent peak delay and coda-attenuation tomography as proxies for seismic scattering and absorption, respectively. The scattering models show high sensitivity to the seismicity. High scattering volumes align with zones of profuse seismicity, such as across the Cucamonga and San Andreas faults, while a channel of low scattering extends from near the San Andreas fault westward. In the vicinity of the Fontana seismic sequence, high absorption, low scattering, and seismicity migration across a fault network suggest fluid-driven processes. Our attenuation and fault network imaging characterize near-fault zones and rock-fluid properties beneath the study area for future improvements in seismic hazard evaluation.

Citation
Nardoni, C., & Persaud, P. (2024). Evidence for faulting and fluid-driven earthquake processes from seismic attenuation variations beneath Los Angeles. Scientific Reports, (under review). doi: 10.21203/rs.3.rs-4228640/v1.