In April 2015, the lower locked portion of the Main Himalayan Thrust ruptured beneath Nepal, causing the disastrous Mw 7.8 Gorkha earthquake. Elucidating the enigmatic geometry of this plate boundary fault is important for understanding the nucleation and arrest of large earthquake ruptures as well as the seismic hazard, topography and tectonics of the Himalaya. Here we interpret the geometry of the Main Himalayan Thrust from the spatial distribution and rupture patterns of a dynamic sequence of aftershocks following the Gorkha earthquake, which were recorded by a rapidly deployed dense seismic network. We find that the thrust comprises two north-dipping subhorizontal planes that are connected by a system of bounded imbricate thrust faults; this structure is known as a duplex. We propose that this duplex acts as an impediment to plate convergence and accommodates tectonic stress along its complex system of faults. Such a prominent structure to the Main Himalayan Thrust is consistent with surface geological studies but challenges geophysically derived conventional models with simpler geometries.
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The waveform dataset and metadata are unrestricted and freely available through the IRIS Data Management Center website (https://ds.iris.edu/ds/nodes/dmc/) under network code ‘XQ: Rapid Response to the Mw 7.9 earthquake of April 25, 2015 in Nepal’. The data that support the findings of this study can be obtained by referring to the supplementary information or contacting the author.
Codes used to generate the results of this study are available through the contact information from the original publications. Requests for further materials should be directed to the corresponding author.
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We thank the Department of Mines and Geology in Nepal for the opportunity to collaborate on science that will help build communities that are more resilient to future earthquakes. This experiment was made possible by the field crew who helped install and maintain the seismic network, including C. Timsina, D. R. Tiwari, M. Pant, K. Pandey, N. Thapa, J. Braunmiller, K. Galvan, V. Kuna, J. Nakai, E. Patlan and many more Nepalese geologists and geophysicists. Special thanks to J. Nábělek for participating in the fieldwork and many stimulating discussions. We thank D. Robinson and D. Hazarika for their constructive comments, which helped to greatly improve the manuscript. The seismic instruments were provided by IRIS through the PASSCAL Instrument Center at New Mexico Tech and participating universities. This collaborative project is funded by the NSF-RAPID and NSF Geophysics programmes, award numbers 1620655 and 1546622.
The authors declare no competing interests.
Peer review information Primary Handling Editor(s): Melissa Plail; Stefan Lachowycz.
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Mendoza, M.M., Ghosh, A., Karplus, M.S. et al. Duplex in the Main Himalayan Thrust illuminated by aftershocks of the 2015 Mw 7.8 Gorkha earthquake. Nat. Geosci. 12, 1018–1022 (2019). https://doi.org/10.1038/s41561-019-0474-8
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