Postseismic deformation following the 2013 Mw 7.7 Balochistan (Pakistan) earthquake observed with Sentinel-1 Interferometry

Kang Wang, & Yuri Fialko

Published August 5, 2017, SCEC Contribution #7416, 2017 SCEC Annual Meeting Poster #101

The Mw 7.7 Balochistan earthquake occurred on September 24th, 2013 in southwestern Pakistan. The earthquake rupture was characterized by mostly left-lateral strike slip, with a limited thrust component, on a system of curved, non-vertical (dip angle of 45-75 deg.) faults, including the Hoshab fault, and the Chaman fault at the North-East end of the rupture. We used Interferometric Synthetic Aperture Radar (InSAR) data from Sentinel-1 mission to derive the timeseries of postseismic displacements due to the 2013 Balochistan earthquake. Data from one ascending and two descending satellite tracks reveal robust post-seismic deformation during the observation period (October 2014 to April 2017). The postseismic InSAR observations are characterized by the line of sight (LOS) displacements primarily on the hanging wall side of the fault. The LOS displacements have different signs in data from the ascending and descending tracks (decreases and increases in the radar range, respectively), indicating that the postseismic deformation following the 2013 Balochistan earthquake was dominated by horizontal motion with the same sense as the coseismic motion. Kinematic inversions show that the observed InSAR LOS displacements are well explained by the left-lateral afterslip downdip of the high coseismic slip area. Contributions from the viscoelastic relaxation and poroelastic rebound seem to be negligible during the observation period. We also observe a sharp discontinuity in the postseismic displacement field on the North-East continuation of the 2013 rupture, along the Chaman fault. We verify that this discontinuity is not due to aftershocks, as the relative LOS velocities across this discontinuity show a gradually decelerating motion throughout the observation period. These observations are indicative of a creeping fault segment at the North-East end of the 2013 earthquake rupture that likely acted as a barrier to the rupture propagation. Analysis of Envisat data acquired prior to the 2013 event (2004-2010) confirms creep on the respective fault segment at a rate of 5-6 mm/yr. The creep rate has increased by more than an order of magnitude after the 2013 event. The inferred along-strike variations in the degree of fault locking may be analogous to those on the central section of the San Andreas fault in California.

Key Words
Postseismic relaxation; fault creep

Citation
Wang, K., & Fialko, Y. (2017, 08). Postseismic deformation following the 2013 Mw 7.7 Balochistan (Pakistan) earthquake observed with Sentinel-1 Interferometry. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy