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Pre- and post-seismic deformation related to the 2015, M_w 7.8 Gorkha earthquake, Nepal

Gualandi, Adriano and Avouac, Jean-Philippe and Galetzka, John and Genrich, Joachim F. and Blewitt, Geoffrey and Adhikari, Lok Bijaya and Koirala, Bharat Prasad and Gupta, Ratnamani and Upreti, Bishal Nath and Pratt-Sitaula, Beth and Liu-Zeng, Jing (2017) Pre- and post-seismic deformation related to the 2015, M_w 7.8 Gorkha earthquake, Nepal. Tectonophysics, 714-715 . pp. 90-106. ISSN 0040-1951. doi:10.1016/j.tecto.2016.06.014.

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We analyze time series from continuously recording GPS stations in Nepal spanning the pre- and post-seismic period associated to the M_w7.8 Gorkha earthquake which ruptured the Main Himalayan Thrust (MHT) fault on April 25th, 2015. The records show strong seasonal variations due to surface hydrology. After corrections for these variations, the time series covering the pre- and post-seismic periods do not show any detectable transient pre-seismic displacement. By contrast, a transient post-seismic signal is clear. The observed signal shows southward displacements consistent with afterslip on the MHT. Using additional data from stations deployed after the mainshock, we invert the time series for the spatio-temporal evolution of slip on the MHT. This modelling indicates afterslip dominantly downdip of the mainshock rupture. Two other regions show significant afterslip: a more minor zone updip of the rupture, and a region between the mainshock and the largest aftershock ruptures. Afterslip in the first ~ 7 months after the mainshock released a moment of [12.8 ± 0.5] × 10^(19) Nm which represents 17.8 ± 0.8% of the co-seismic moment. The moment released by aftershocks over that period of time is estimated to 2.98 × 10^(19) Nm. Geodetically observed post-seismic deformation after co-seismic offset correction was thus 76.7 ± 1.0% aseismic. The logarithmic time evolution of afterslip is consistent with rate-strengthening frictional sliding. According to this theory, and assuming a long-term loading velocity modulated on the basis of the coupling map of the region and the long term slip rate of 20.2 ± 1.1 mm/yr, afterslip should release about 34.0 ± 1.4% of the co-seismic moment after full relaxation of post-seismic deformation. Afterslip contributed to loading the shallower portion of the MHT which did not rupture in 2015 and stayed locked afterwards. The risk for further large earthquakes in Nepal remains high both updip of the rupture area of the Gorkha earthquake and West of Kathmandu where the MHT has remained locked and where no earthquake larger than M_w7.5 has occurred since 1505.

Item Type:Article
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Gualandi, Adriano0000-0002-3100-8932
Avouac, Jean-Philippe0000-0002-3060-8442
Additional Information:© 2016 Published by Elsevier B.V. Received 13 February 2016, Revised 7 June 2016, Accepted 9 June 2016, Available online 16 June 2016. The geodetic array of the Department of Mines and Geology (Nepal) was constructed and maintained thanks to Jean-Philippe Avouac's startup funds at the California Institute of Technology, and support from the Gordon and Betty Moore foundation to the Tectonics Observatory at Caltech. We also acknowledge support from the Départment Analyse et Surveillance de l'Environnement (CEA, France). This work would not have been possible without the datasets acquired under two awards: (1) NSF EAR 1345136 to J.P. Avouac and N. Lapusta, at the California Institute of Technology (Galetzka et al., 2015); and (2) a NASA-funded supplement to the GAGE Facility award, under a request framed by J.P. Avouac for UNAVCO engineering support, data recovery and data services. UNAVCO is supported to operate the GAGE Facility by the National Science Foundation (NSF) and National Aeronautics and Space Administration (NASA) under NSF Cooperative Agreement No. EAR-1261833. The Department For Foreign International Development and the National Environment Research Council (UK) also provided support for the post-seismic response. Some of the figures have been created using the Generic Mapping Tools (GMT) software (Wessel and Smith, 1998). Victoria Stevens provided the coupling model and the fault geometry used in this work. Mathilde Radiguet provided some scripts used in the inversion of the geodetic data. We thank Romain Jolivet for discussion and Kristel Chanard for her insight regarding the modelling of the seasonal deformation. We thank the guest editor, Gavin P. Hayes, as well as Roland Bürgmann and one anonymous reviewer for the comments which improved the manuscript.
Group:Seismological Laboratory
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
Départment Analyse et Surveillance de l'EnvironnementUNSPECIFIED
Subject Keywords:Gorkha; Afterslip; ICA; Rate-strengthening; Pre-seismic; Post-seismic; GPS
Record Number:CaltechAUTHORS:20171109-110007329
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Official Citation:Adriano Gualandi, Jean-Philippe Avouac, John Galetzka, Joachim F. Genrich, Geoffrey Blewitt, Lok Bijaya Adhikari, Bharat Prasad Koirala, Ratnamani Gupta, Bishal Nath Upreti, Beth Pratt-Sitaula, Jing Liu-Zeng, Pre- and post-seismic deformation related to the 2015, Mw7.8 Gorkha earthquake, Nepal, In Tectonophysics, Volumes 714–715, 2017, Pages 90-106, ISSN 0040-1951, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83105
Deposited By: Tony Diaz
Deposited On:09 Nov 2017 22:45
Last Modified:15 Nov 2021 19:55

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