Coseismic fault-propagation folding during the 2015 Mw 5.7 Dajal earthquake on the Sulaiman Fold and Thrust belt from Sentinel 1A
Year: 2021
Type: conference-paper
Abstract: The continental collision at the western boundary of the Indian continent formed the tectonically \ncomplex transpressional zones of the Sulaiman Fold Thrust (SFT) and Kirthar Fold Thrust (KFT) belts. \nSeismic hazard around the SFT is considered elevated, but shortening across its eastern boundary is \npoorly understood because of the scarcity of moderate-sized earthquakes in the last decades. Here, \nwe use Sentinel-1A interferometry to analyze the coseismic crustal deformation and source fault \ngeometry associated with the 2015 moment magnitude (Mw) 5.7 Dajal earthquake that occurred on \nthe boundary thrust in the SFT belt. The line-of-sight displacements amount to ~45 and ~50 mm for \nthe ascending and descending interferograms, respectively, due to thrust-dominated slip over a blind \nfault. The inverted InSAR measurements fit well with USGS and ISC model parameters, except for the \ndepth of the fault that is found to be shallower. A simplified fault model shows a dip of 41°, strike of \n194° and rake of 79°, with a large aspect ratio of the seismogenic fault, due to a narrow ruptured \nfault width compared to the ruptured length. The InSAR inverted fault source parameters are used \nto determine the seismic moment (Mo = 3.94 × 1017 Nm), with the shear modulus (μ = 32 GPa), \ncorresponding to a moment magnitude Mw = 5.7 that is consistent with seismological estimates. We \nalso perform the sensitivity analysis to understand the geometry of a possible ramp-décollement or \ndécollement-ramp-décollement fault system using finite fault inversion. Finite fault modeling \nindicates the presence of a shallow décollement branching into a shallow ramp and décollement at \napproximately 7 km depth. We also incorporate the flexural slip over axial surface during coseismic \ndeformation. The Dajal earthquake seems to have propagated along the base of the ramp and \nassociated axial surface, that stops at the tip of the ramp. A few aftershocks occurred in the \nsurrounding anticline. We suggest that folding of the shallow sediments by flexural slip at the eastern \nboundary of the SFT belt may have restricted the rupture propagation.
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3204497797