S42C-08
Postseismic Deformation Following the April 2015 M7.8 Nepal Earthquake Measured Using Sentinel-1A Interferometry
Thursday, 17 December 2015: 12:05
305 (Moscone South)
Thomas Francis Ingleby1, Tim J Wright2, Pablo J González3, Andrew J Hooper3 and John R Elliott4, (1)University of Leeds, Leeds, United Kingdom, (2)University of Leeds, COMET, School of Earth and Environment, Leeds, LS2, United Kingdom, (3)University of Leeds, COMET, School of Earth and Environment, Leeds, United Kingdom, (4)University of Oxford, COMET, Department of Earth Sciences, Oxford, United Kingdom
Abstract:
The evolution of postseismic deformation following large earthquakes plays a significant role in determining future regional seismic hazard. Patches of the coseismic fault plane that failed to rupture in the initial earthquake may fail in future damaging earthquakes or release stress by slipping aseismically. Furthermore, postseismic deformation offers a rare opportunity to probe the rheology of fault zones, providing important constraints for models of the earthquake deformation cycle.
The April 2015 M7.8 Gorkha (Nepal) earthquake ruptured a major thrust fault beneath central Nepal. Rupture began at ~15 km depth and appears to have propagated laterally along a shallow decollement. Geodetic and seismological observations suggest that most coseismic slip occurred on the deepest half of the fault plane, between the ramp under the high Himalaya and Kathmandu. 50 km of the fault south from Kathmandu to the Main Frontal Thrust did not fail coseismically, consistent with a lack of clear surface ruptures.
Analysis of GPS data suggests the entire Main Himalayan Thrust (MHT) is locked from the surface to the depth of the Gorkha earthquake. The behaviour of the MHT to the west and up-dip of the Gorkha earthquake in the postseismic period is essential for our understanding of the ongoing seismic hazard. These sections of the fault may be relieving stresses aseismically or still be accumulating stresses which could be released in future, large earthquakes. Attempting to answer why these sections of the fault are behaving as they are will also place constraints on fault zone rheology.
The launch of ESA's Sentinal-1A allows for monitoring of postseismic deformation every 12 days over a large area. This short repeat time and large coverage allows us to investigate the spatial and temporal evolution of postseismic deformation in great detail and complements GPS results from the region. We will present a preliminary analysis of postseismic deformation in the 6 months following the earthquake using data from Sentinel-1A. Preliminary results suggest little postseismic deformation up-dip of the 2015 rupture.
