Lateral Variations of Interseismic Coupling along the Himalayan Arc in Bhutan : Clues from Time Series Analysis of Sentinel-1 InSAR Data ?

Abstract

A recent GPS study suggests interseismic coupling variations along the Main Himalayan Thrust in Bhutan, with implications on the regional seismic potential (Maréchal et al., 2016). We use the complete Sentinel-1 radar data acquired since 2014 along descending and ascending orbits to provide average velocity maps across the front range in Bhutan, based on radar interferometry (InSAR). We compare results from time series analysis from a Small Baseline Subset approach (NSBAS, Doin et al., 2011, Grandin, 2015) and Distributed Scatterers Interferometry techniques to better assess and mitigate the various sources of noise in our data set (Ansari et al., 2018, De Zan et al., 2015). We correct tropospheric delays using global atmospheric models (ERA5, ECMWF) and ionospheric delays with split-spectrum technique (Gomba et al., 2016), to improve the quality of the deformation signal especially at large scale. We finally confront GPS and InSAR velocity profiles across range through simple 2D elastic modelling to better constrain the displacement rate across the range and discuss the existence of shallow creep in eastern Bhutan, as suggested by GPS data.