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Strong along-strike variation in aftershock distribution and rupture propagation of 2015 Mw 7.8 Gorkha earthquake in Nepal

Abhijit Ghosh, Bo LI, & Manuel M. Mendoza

Published August 15, 2016, SCEC Contribution #6938, 2016 SCEC Annual Meeting Poster #251

Gorkha earthquake presents a unique opportunity to study active tectonics, earthquake dynamics and fault structure in the Himalayas in Nepal. We use four large aperture seismic arrays at teleseismic distances to image the rupture propagation of the mainshock and aftershock activities immediately following it. In addition, a dense local network of 45 seismic stations is deployed after the mainshock covering the entire rupture area to capture the aftershock activities.

We calibrate and combine four large aperture seismic arrays to image rupture propagation in unprecedented resolution. It shows rupture complexities and branching near the end of this damaging quake. Moreover, we solely use the arrays to detect and locate aftershock activities immediately following the mainshock. The aftershock distribution determined only by the arrays matches well with the standard global earthquake catalog, but detects more than twice as many aftershocks during the same time period. It shows that existing seismic arrays alone can be used to rapidly detect more aftershocks and determine their spatiotemporal distribution to help hazard assessment and fast response right after a destructive earthquake.

Furthermore, we use the dense local seismic network to detect and locate aftershock activities with local magnitude as low as 0.3. Relative relocations of microseismicity provide a high-resolution image of the fault structure in this area. They illuminate a gently dipping decollement with several steeply dipping faults, which are responsible for majority of the aftershock production. Moreover, there is a sharp along-strike variation in aftershock distribution, possibly related to the mainshock rupture and underlying structure. This study is providing new insights into the dynamics of the Gorkha earthquake, structures in the Himalayan fault system and their implications in the seismic hazards in this region.

Key Words
Gorkha, Nepal, aftershock, array, rupture

Ghosh, A., LI, B., & Mendoza, M. M. (2016, 08). Strong along-strike variation in aftershock distribution and rupture propagation of 2015 Mw 7.8 Gorkha earthquake in Nepal. Poster Presentation at 2016 SCEC Annual Meeting.

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