Reconciling Fault Geometry in Nepal Himalaya using the “NAMASTE” Seismic Network

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

Submitted August 15, 2017, SCEC Contribution #7862, 2017 SCEC Annual Meeting Poster #060

The Mw 7.8 Gorkha earthquake in April of 2015 produced ~8 m of peak co-seismic slip as the Main Himalayan Thrust (MHT) fault ruptured 130 km east, under dense population centers such as Kathmandu. The mainshock and subsequent aftershocks killed over 9,000 people and left more than 2 million displaced from their home, from a combination of infrastructure failure and triggered landslides. Since the MHT did not fully rupture to the surface, there is continued concern that another large damaging earthquake in this region is likely to occur in the very near future. To rapidly assess the evolving state of stress in Nepal, we developed and deployed a dense, 45-station, seismic network (“NAMASTE”) that operated from June 2015 to May 2016. Composed of broadband, short-period, and strong motion sensors, each separated by ~20 km, NAMASTE captured the dynamic sequence of aftershock behavior by blanketing the 27,650 km2 rupture area. With one years worth of data, we generate a high-resolution earthquake catalog using the Antelope software environment, and the relative relocation capabilities of HypoDD [Waldhauser & Ellsworth, 2000]. We obtain over 7,000 precisely located earthquakes that tightly cluster to illuminate the complex Himalayan fault system with unprecedented resolution. We observe the MHT to lie between depths of 10 to 20 km in the rupture area, as it extends down-dip beneath the Eurasian plate. Moreover, we observe steeply dipping faults that collectively resemble a duplex structure above the MHT, which may have been previously undetected due to seismic inactivity or lack of instrumentation in the past. The patterns in seismicity imaged in this study are possibly reflecting structural and frictional heterogeneities along the Indian-Eurasian plate boundary, providing greater insight on complex fault structures and physical processes controlling the earthquake cycle in Nepal.

Mendoza, M. M., Ghosh, A., Karplus, M. S., Nabelek, J., Sapkota, S. S., Adhikari, L. B., Klemperer, S. L., & Velasco, A. A. (2017, 08). Reconciling Fault Geometry in Nepal Himalaya using the “NAMASTE” Seismic Network. Poster Presentation at 2017 SCEC Annual Meeting.

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