Triggering Intensity Changes over Time and Space in Southern California

Huiyun Guo, Emily E. Brodsky, & Masatoshi Miyazawa

Submitted September 8, 2024, SCEC Contribution #13783, 2024 SCEC Annual Meeting Poster #033

Dynamic triggering of earthquakes is when seismic waves from earthquakes induce seismic activity at a distance. The observability of the seismic wave stresses and their results presents a unique opportunity to understand earthquake interactions and associated hazard implications. The extent and timing of dynamic triggering at given specific stress changes still remain inadequately predicted due to limited studies and datasets. In particular, the requirement for complete, well-characterized catalogs to detect triggering systematically seriously limits the types of studies possible. To address this, we utilized 7-year continuous waveform data from 239 stations in southern California and used PhaseNet for phase picking to identify local earthquakes and measure triggering without constructing any earthquake catalog. We map the triggering intensity over the region and find that overall, the Mojave segment of the San Andreas is the most easily triggered region. However, the spatial pattern changes after the Ridgecrest earthquake and the area becomes much less prone to triggering. The sensitivity to dynamic triggering in Southern California shows that the stress state was changed by the MW 7.1 Ridgecrest earthquake, particularly for seismic active regions. For a while, at least, Southern California appears safer, possibly due to the transient triggering of the population of faults that had previously been near failure. We further observe a slow decay rate of dynamic triggering and conclude that low-frequency waves (0.04-0.1 Hz) may be more effective in dynamic triggering than high-frequency waves (1-3 Hz) which is consistent with a rate-state assisted aseismic creep or hydrological triggering mechanism.

Key Words
Earthquakes, Faults, Seismology, Dynamic triggering, Stress state

Citation
Guo, H., Brodsky, E. E., & Miyazawa, M. (2024, 09). Triggering Intensity Changes over Time and Space in Southern California . Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology