Coseismic Folding During Ramp Failure at the Front of the Sulaiman Fold‐and‐Thrust Belt

Abstract

The Sulaiman Fold Thrust (SFT) in Central Pakistan formed during the India-Eurasia collision in the late Cenozoic. However, the mechanics of shortening of the brittle crust at time scales of seismic cycles is still poorly understood. Here, we use radar interferometry to analyze the deformation associated with the 2015 magnitude (Mw) 5.7 Dajal blind earthquake at the eastern boundary of the SFT. We use kinematic inversions to determine the distribution of slip on the frontal ramp and of flexural slip along active axial surfaces for the forward- and backward-verging two end-member models: a double fault-bend-fold system and a fault-propagation-fold. In both models, a décollement branches into a shallow ramp at approximately 7.5 km depth with coseismic folding in the hanging wall. The Dajal earthquake ruptured the base of the Boundary Thrust buried under the sediment from the Indus-River floodplain, representing fault-bend or fault-propagation folding some 30 km off its nearest surface exposure.