Permanent Co-seismic Deformation of the 2013 MW7.7 Baluchistan, Pakistan Earthquake from High-resolution Surface Strain Analysis

Earthquake-generating faults are commonly surrounded by features such as topography and damage zones that indicate that earthquakes induce some degrees of permanent (inelastic) deformation. Quantifying the magnitude and extent of co-seismic inelastic deformation within single earthquakes has been a long-standing goal in earthquake research as a means to relate single earthquakes to the long-term faulting record . Recent advances in geodetic imaging approaches with optical imagery and high-resolution topography provide new approaches to address this question. In this study, we detail c o-seismic permanent deformation using surface strain magnitudes inferred from imaging geodesy observations. We invert SPOT-5 and WorldView optical imagery pixel-tracking displacements for 30-m resolution co-seismic surface strain fields of the 2013 Mw7.7 Baluchistan, Pakistan strike-slip earthquake. We observe near-fault positive dilatation strains, indicative of co-seismic fault zone expansion. We define permanent fault zone width (PFZW) as the near-fault extent where strain magnitude exceeds the elastic yield limit for common rocks (~0.5%). We show that inelastic failure is localized within a zone of consistent 100-120 m width along the rupture trace. The PFZW does not show clear correlation to varing off-fault deformation or surficial material types. Instead, by comparing our results to those calculated from other recent earthquakes, we found that the PFZW is consistent with scaling relationships between fault maturity (as defined by cumulative offset) and damage zone width. Therefore, we argue that the observed permanent deformation zone reflects active deformation of the fault damage zone.