# Characterizing Micro-Displacements on Active Faults in the Gobi Desert with Time-Series InSAR
## 1 Introduction  
Beishan lies in northwest China and is strategically important for nuclear safety, as it is a potential site for a geological disposal facility (GDF) to permanently isolate and dispose of high-level radioactive waste (HLW) by burial in an engineered underground facility in the local granite region. The Jiujing granite region at Beishan was chosen for investigation through the application of the persistent scatterer Interferometric synthetic aperture radar technique (PSI). This area is dominated by the Gobi Desert and by several large, east-west elongated granite plutons including Jiujing, Xinchang, Jiijicao, Yemaquan, Suanjingzi, and Shazaoyuan. A detailed understanding of the local structural geology is essential and is achieved by identifying, mapping, quantifying, and characterising the active faults. The term 'wrench fault' refers to a high angle strike-slip fault of great linear extent, which formed in response to horizontal pure shear [1]. Such faults are characterised by the attributes of lateral-slip evidence, steep fault plane, and complex deformation zonesof subsidiary faults, and they often occur in regional-scale basement rocks. The collision between the Eurasian and Indian Plates along the Himalayan Mountain belt has resulted in prominent compressional wrench faulting in the Jiujing region of northwest China [2]. Active faults are frequently detected with differential InSAR (DInSAR), if the displacement is sudden or significant, or with time-series InSAR techniques such as PSI, if displacements are small or slowly developing. The details will be explained in Section 3.2. Chronologically, the following are a series of studies investigating the tectonic faults through time-series InSAR techniques. [PERSON] [3] first detected the differences in ground subsidence over the Rio\(-\)Antirio area in Western Greece and suggested that the subsidence rates at Rio (\(-1.8\) to \(-6.2\) mm a\({}^{-1}\)) were much higher than those at Antirio (\(-2.0\) mm a\({}^{-1}\) or less). It is suggested that subsidence was mainly attributed to the presence of active faults in the centre, with Rio located in the hanging wall side of the fault zone. Then, [PERSON] [4] monitored the crustal deformation in the L'Aquila area in central Italy based on deformation gradients and identified that most active faults were NW-SE striking and dipped to the SW. After that, [PERSON] [5] observed the interseismic deformation along the Longitudinal Valley Fault (LVF) in Eastern Taiwan, China and found that there was a clear velocity discontinuity along the fault, with a 3 mm a\({}^{-1}\) velocity offset due to shallow interseismic creep. This improved the mapping of local active tectonic structures. At the same time, [PERSON] [6] measured a 10 mm a\({}^{-1}\) average velocity difference between the hanging wall and footwall sides of the Central Camionera Fault and a maximum land subsidence around 7-8 mm a\({}^{-1}\) in Morelia, Mexico. However, it was concluded that this was the result of groundwater overexploitation rather than tectonic fault activity, where the fault planes in Morelia only acted as a barrier to the horizontal migration of groundwater. Two years later in 2014, [PERSON] [7] investigated the impacts of groundwater exploitation and fault activity on ground subsidence in Datong Basin, China, using the small baseline subset (SBAS) method, and measured a 6 mm a\({}^{-1}\) subsidence difference between the two sides of F8 ground fissure, indicating the local ground subsidence was controlled by the Kou-Quan and Datong-Yanggao Faults and surrounding fissures. In a different study [8], the ground deformation in Taiyuan Basin was also investigated, and it was suggested that the local subsidence was also a result of fault activity.