Co- and Post-seismic deformation due to the 2016 moderate earthquake sequence at the Chaman fault

The Chaman fault system forms a transform boundary between Indian and Eurasian plates in Pakistan and Afghanistan. Previous geological surveys find the relative velocity of the Indian plate to the Eurasian plate at around 40mm/yr. However, no large earthquakes (M>7) have been observed on the Chaman fault which is a ~900km long major sinistral strike-slip fault in the system. Low seismicity results from either a long recurrence interval or aseismic creeping. Recent studies suggest a heterogeneous distribution of locked and creeping segments along the fault (Fattahi and Amelung, 2016; Barnhart, 2016). In a previous work, Furuya and Satyabala(2008) showed a long lasting and spreading afterslip following a moderate earthquake (M5) in 2005 on the fault , where no creeping signals were detected prior to the earthquake.

We focus on two moderate events occurred on May 13 and July 10 in 2016 on the fault, which were first M5-class events since the 2005 M5 event examined by Furuya and Satyabala (2008). We use ascending Sentinel-1 SAR data from December 2, 2015 to March 2, 2017. We generate InSAR images that suggest the co- and post-seismic, cumulative deformation of left-lateral strike-slip. Especially the second July 10 event has very similar behavior with the result in Furuya and Satyabala (2008).

Because of the short wave length, our interferograms are still affected by atmospheric noises even after averaging some images using different master dates. We next perform InSAR time series analysis to separate deformation signals from other temporally random errors. InSAR time series analysis is based on a linear least squares inversion which translates the set of interferograms into a range change time series. We will use 55 interferograms from 11 SAR data to obtain LOS vectors, following a method from Schmidt and Bürgmann (2003).