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A Systematic Investigation into Dynamic and Delayed Earthquake Triggering in a Seismically Hazardous Himalayan Fault Segment

Manuel M. Mendoza, Bo Li, Abhijit Ghosh, & Shyam S. Rai

Published August 15, 2019, SCEC Contribution #9859, 2019 SCEC Annual Meeting Poster #082

Observations of remote earthquake triggering by the passage of teleseismic waves is well-documented [e.g. Prejean et al., 2015; Ghosh et al., 2009]; however, the mechanisms driving both the “dynamic” and “delayed” facets of this phenomenon remain largely unclear. Therefore, it is imperative to garner a holistic understanding of the physical interactions between teleseismic waves and critically-stressed faults. In this study, we investigate a 500-km seismically-quiescent fault segment in the Himalayas — what is known specifically as the “central Himalaya seismic gap” where a major (or great) earthquake is overdue — that exhibits an inordinate sensitivity to dynamic stresses imparted by large distant earthquakes [Mendoza et al., 2016]. With the development of a robust earthquake catalog obtained from a broadband seismic network that blanketed the state of Uttarakhand, India, between 2006 and 2008, we observe and closely examine four instances of teleseismic events triggering heightened local seismicity. The catalog is then expanded upon using the matched-filter technique to detect and locate considerably more triggered events. In this preliminary catalog, we note three immediate and interesting features amongst each of those four triggering instances: (1) for a period of time, earthquakes are tightly clustered in space; (2) are occurring at depths below 30 km; and (3) decay in frequency down to ambient seismicity levels in an Omori-law-like manner. Following these observations, earthquake moment tensor solutions are computed to identify the type of faulting (i.e. orientation and sense of slip of the fault plane) that makes this region susceptible to triggering. Lastly, we quantify the dynamic stresses of the four teleseismic events that caused triggering, and those that did not, to approximate a minimum stress threshold for triggering in this thrust fault regime. This study sets out to investigate the state of stress of faults and the combination of conditions that cause them to fail, through the lens of remote triggering, while also providing valuable insight into tectonic processes governing the future seismic hazard of this prevailing unruptured Himalayan fault segment.

Mendoza, M. M., Li, B., Ghosh, A., & Rai, S. S. (2019, 08). A Systematic Investigation into Dynamic and Delayed Earthquake Triggering in a Seismically Hazardous Himalayan Fault Segment. Poster Presentation at 2019 SCEC Annual Meeting.

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