Delayed Triggering of small Local Earthquakes near the San Jacinto Fault after the 2014 Mw 7.2 Papanoa Earthquake

Bo Li, & Abhijit Ghosh

Submitted August 14, 2018, SCEC Contribution #8606, 2018 SCEC Annual Meeting Poster #070

We find evidence of delayed triggering of small earthquakes off San Jacinto Fault (SJF) near the Anza Gap. We develop a move max matched-filter method to analyze seismicity that occurred near the SJF one month before and after the 2014 Mw 7.2 Papanoa earthquake. During this period, there are 880 local events in this area recorded by the Advanced National Seismic System (ANSS) and the Southern California Seismic Network (SCSN) catalog. Using the catalog events as templates, the move max matched-filter method detects 5.4 times of catalog earthquakes, while the matched-filter method only distinguishes 3.2 times of catalog events using the same detection threshold. The seismicity rate increases significantly few hours after the passage of the seismic waves of the Papanoa earthquake and the high seismic rate persists for about one week. Interestingly, the most heightened seismicity is located west to the SJF (off SJF) and city Anza, on an apparently unmapped blind fault that strikes nearly perpendicular to the SJF and steeply dips to the northwest. We speculate that more than one mechanisms may be responsible for this delayed triggering. The transient dynamic stresses may have triggered a slow slip or fault creep, and lead to the increased and protracted seismicity along the San Jacinto Fault (SJF). Alternatively, a time-dependent acceleration to failure process initiated by the dynamic stress change may result in the enhanced seismicity on the blind fault. The newly discovered fault points out existence of additional fault structure (off SJF), which may be capable of producing damaging earthquakes near or within the Anza seismic gap.

Li, B., & Ghosh, A. (2018, 08). Delayed Triggering of small Local Earthquakes near the San Jacinto Fault after the 2014 Mw 7.2 Papanoa Earthquake. Poster Presentation at 2018 SCEC Annual Meeting.

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