[S-SS07] Environmental Seismology: from deep earth to surface process

[SSS07-P11] Spatiotemporal Dependence of Foreshock-Mainshock Sequences in South California

*Hong Peng¹, James Mori² (1.The Institute of Statistical Mathematics, 2.Kyoto University)

Keywords:Foreshock, ETAS, Prediction

Foreshock-mainshock sequences are one of the most prevalent phenomena in seismology. However, distinguishing the foreshocks from universal seismicity remains significant challenging, particularly in the existence of frequent aftershocks. The underlying physical mechanisms which driving the foreshock-mainshock sequences are not yet fully understood. Here we use a high-resolution earthquake catalog (Quake Template Matching) in conjunction with the epidemic-type aftershock sequences model (ETAS model) to investigate the foreshock-mainshock sequences in southern California. Our analyses of over 800 Mw >= 3.5 mainshocks reveal that most foreshocks typically occur within distances of less than 3 km and times up to 90 days prior. It is possible to use a power law decay to estimate the spatial and temporal distributions of potential foreshocks. The results suggest that foreshock-mainshock sequences are primarily triggered by the stresses that extending over a few kilometers and persisting for months, but showing limited dependence on mainshock magnitude. Additionally, we present quantitative estimations of foreshock occurrence rates across various distance and time intervals, which can provide enhancements for the earthquake hazard assessments.