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Capturing Frictional Asperities along the Complex Structure of the Main Himalayan Thrust in Nepal after the 2015 Mw 7.8 Gorkha Earthquake

Manuel M. Mendoza, Bo Li, Abhijit Ghosh, Marianne S. Karplus, John Nabelek, Soma N. Sapkota, Lok B. Adhikari, Simon L. Klemperer, & Aaron A. Velasco

Published August 15, 2018, SCEC Contribution #8806, 2018 SCEC Annual Meeting Poster #092

The 2015 Mw 7.8 Gorkha earthquake produced 4 m of peak co-seismic slip as the Main Himalaya Thrust (MHT) ruptured eastward under the dense population centers, such as Kathmandu. The aftermath of destruction left over 9,000 people killed, and more than 2 million displaced from their homes due to both infrastructure failure and seismically triggered landslides throughout the High Himalaya. There is concern that since the MHT did not fully release much of its strain by rupturing to the surface, that another large damaging earthquake could occur. Our group, in collaboration with other institutions, rapidly assessed the evolving state of stress in the region via the deployment of “NAMASTE”, a 45-station seismic network composed of a mix of broadband, short-period, and strong motion sensors, that operated from June 2015 to May 2016. Blanketing the 27,650 km2 rupture area, and beyond, we obtain a catalog containing over 7,000 precisely located earthquakes that range in local magnitude from 0.3 to 6.5. A result of particular interest from these locations, is the illumination of both a shallow dipping MHT, and a set of high-angle faults that we infer to be components for a duplex structure. The investigation presented here aims to understand the frictional properties of the duplex structure with relation to the MHT, through analyses of b-value mapping and repeating earthquakes. The b-value has been observed to vary laterally and with depth in this area; in particular, we observe a significantly low b-value area in the easternmost end of the network where the duplex structure is illuminated, which could be reflecting the presence of asperities, or stress concentrations. In addition, using the catalog events, we find many repeating earthquakes. Repeating earthquakes are inferred to occur as a result of repeated failure of small asperities that are surrounded by a stable and continuous sliding area along the fault. By reconciling a relationship in both space and time between areas of low b-value and where repeating earthquakes occur, our goal is to gain valuable insights into the frictional properties along the MHT that may control the recurrence of the next large event in Nepal, Himalaya.

Mendoza, M. M., Li, B., Ghosh, A., Karplus, M. S., Nabelek, J., Sapkota, S. N., Adhikari, L. B., Klemperer, S. L., & Velasco, A. A. (2018, 08). Capturing Frictional Asperities along the Complex Structure of the Main Himalayan Thrust in Nepal after the 2015 Mw 7.8 Gorkha Earthquake. Poster Presentation at 2018 SCEC Annual Meeting.

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