Surface crustal deformation is often used to explore physical processes within the interior of the Earth. The observable surface changes can reflect variable subsurface physical processes that are usually inaccessible to modern instruments. For example, surface displacement observations have been widely used to study the geometric parameters of faults and slip distributions of earthquakes, to estimate interseismic slip rates and locking depths of active faults, and to constrain the physical properties of rock at depth. Therefore, a comprehensive knowledge of crustal deformation plays a key role in evaluating the seismic hazard probability in areas with active faults, particularly for heavily populated areas such as the North-South (Nanbei) Seismic Belt in western China.
The two most widely used techniques for monitoring crustal movement are the Global Navigation Satellite System (GNSS) and interferometric synthetic aperture radar (InSAR). The former involves extensive fieldwork and is only applicable at locations with convenient transportation facilities. The latter can cover a relatively large region at significantly lower cost. With the increase of SAR data since the launch of Sentinel-1A satellite in 2014, InSAR has been the preferred tool for monitoring crustal deformation. Thus, there is an urgent need for a proficient application of this technique. Based on the iGPS time series analysis package, we developed a suite of programs that incorporate the open source InSAR software-GMTSAR to automate and facilitate the processing procedure of time series InSAR analysis. It can automatically download data, organize the interferometric processing tasks, perform time series, conduct data analysis, and visualize results. We first introduce the interferometric functionalities of GMTSAR and iGPS software. The processing flowchart is described in detail by deriving the present-day slow crustal deformation of the western Tibetan Plateau as an example. Owing to high coherence inherently for the Tibetan Plateau, using Sentinel-1 ascending track T12 data collected during June 2015 to September 2022, we demonstrated that a dense InSAR average velocity map of high accuracy could be obtained for a vast area spanning over 1000 km. The InSAR results showed that the eastward extrusion of the Tibetan Plateau resulted in rapid shear slip within a narrow belt between the Altyn Tagh and Margai Caka-Kunlun fault zones, absorbing over half of the relative motion between the Tarim Basin and Tibetan Plateau.
This study systematically introduced how to perform automated small baseline subset (SBAS) InSAR processing using open-access SAR data and InSAR software to detect subtle crustal deformation. In the future, InSAR operators can apply this method to conduct their own processing chains for crustal deformation studies with limited inputs.