Group , Poster #213, Seismology

Long-base seismic interferometry reveals a hidden slow-slip event near the Anza seismic gap

Yixiao Sheng, Aurélien Mordret, Korbinian Sager, Florent Brenguier, Pierre Boué, Baptiste Rousset, Frank L. Vernon, & Yehuda Ben-Zion
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Poster Presentation

2021 SCEC Annual Meeting, Poster #213, SCEC Contribution #11435 VIEW PDF
Aseismic slip, now recognized as a ubiquitous phenomenon, has been observed at all kinds of plate boundaries. Slow-slip events occurring along active faults can accommodate a large portion of the slip budget, and their occurrence has also been recognized as a potential driving mechanism for major earthquakes. Despite substantial improvements in geodetic observations, the noise level inhibits the detection of small SSEs, impeding our ability to describe the complete spectrum of transient slips and their role in seismic cycles. On the other hand, anthropogenic seismic sources, such as freight trains and cars, have attracted more and more attention. They generate strong seismic signals, especia...lly at high-frequency bands, valuable for inverting velocity structures and monitoring changes. We use the freight trains running through the Coachella Valley as repeating sources and perform 10-year seismic velocity monitoring of the San Jacinto Fault near the Anza area, CA. We detect and map a 2-month episode of seismic velocity change. We interpret this velocity perturbation as a result of a slow-slip event that happened near the edge of the Anza seismic gap. We further validate this interpretation using numerical simulations. The preferred dislocation occurred near the bottom of the geodetic locking depth, which supports the existence of a transition zone with heterogeneous frictional prosperities between the shallow velocity-weakening and the deep velocity-strengthening regions. Our approach opens up a new prospect for continuously monitoring fault systems. It will contribute to understand the interaction between aseismic and seismic slips and provide more complete characterizations of earthquake hazards.
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