InSAR Time-series Analysis of Afterslip from the 2017 Mw 7.3 Sarpol-e Zahab (Darbandikhan) Earthquake: Imaging Sub-surface Structure from Geodesy and Analytical and Numerical Models

Abstract:

In November 2017, the Mw 7.3 Sarpol-e Zahab (Darbandikhan) earthquake ruptured a blind basement fault beneath the Zagros fold and thrust belt of Iran. Aseismic afterslip immediately followed the earthquake and produced surface deformation measurable through InSAR time series analysis. Previous studies of this post-seismic signal suggested that triggered afterslip occurred up-dip of the earthquake on the basal decollement of the Zagros Mountains. A currently unresolved issue is whether afterslip also occured on additional structures, such as down-dip of the co-seismic. Another key problem is that, given that the afterslip faults are blind, inversions of InSAR time series displacements for the causative fault geometry of afterslip are non-unique, and the surface displacements can be fit by a range of reasonable fault configurations that each have important implications for sub-surface structure in the Zagros. In this study, we use InSAR time series analysis from the Sentinel-1 satellite to generate a time-series spanning two years of afterslip deformation. We invert surface displacements for the time varying slip distribution of afterslip on a suite of candidate fault geometries. We additionally present a suite of mechanical models that are designed to both explore the frictional properties of the faults on which afterslip occurs, as well as to discriminate between different fault geometry configurations that are not uniquely constrained by the fault slip inversions alone. This research represents an effort to undertake structural imaging with geodetic observations by combining analytical and numerical modeling approaches.