POSTSEISMIC DEFORMATION FOLLOWING THE APRIL 25, 2015 GORKHA EARTHQUAKE: AFTERSLIP VERSUS VISCOUS RELAXATION
François Jouanne  1@  , Ananta Gajurel, Jean Louis Mugnier, Laurent Bollinger, Lok Bijaya Adhikari, Bharat Koirala, Nathalie Cotte, Pascale Bascou, Pascale Huyghe  1@  
1 : Institut des sciences de la Terre  (ISTerre)  -  Website
CNRS : UMR5275, IFSTTAR, IFSTTAR-GERS, Université de Savoie, Université Joseph Fourier - Grenoble I, INSU, OSUG, Institut de recherche pour le développement [IRD] : UR219, PRES Université de Grenoble
BP 53 38041 Grenoble cedex 9 -  France

The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.8) is estimated in this paper based on a cGNSS network installed prior to the earthquake and supplemented by cGNSS stations installed after the main shock. Postseismic velocities are obtained from recorded velocities corrected for interseismic deformation and seasonal variations. The maximum postseismic displacement is found north of the rupture area, where locally it reached 100 mm between the date of the earthquake and late 2016. The postseismic deformation affects the northern part of the rupture area but not the southern part, along the southern part of the Main Himalayan Thrust. Three hypotheses for the mechanisms controlling postseismic deformation are tested through numerical simulations of the postseismic time series: (i) viscous relaxation, (ii) afterslip, or (iii) a combination of these two mechanisms. We can exclude postseismic deformation controlled by viscous relaxation of a thick deformation zone along the northern and lower flat of the MHT. However, it is impossible to discriminate between postseismic deformation controlled by either afterslip along the MHT (northern part of the rupture zone, crustal ramp, and lower flat of the MHT) or a combination of afterslip along the MHT (northern part of the rupture zone, crustal ramp) and viscous relaxation along a thin (~3 km thick) low-viscosity body centered on the lower flat of the MHT.


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