Xiaoyong Wu

High-precision and high-resolution surface deformation provide crucial constraints for studying the kinematic characteristics and dynamic mechanisms of crustal movement. Considering the limitations of existing geodetic observations, we used Sentinel-1 SAR images and accurate GNSS velocity to obtain a high-resolution three-dimensional (3D) surface velocity map across the Laohushan segment and the 1920 Haiyuan earthquake rupture zone of the Haiyuan Fault on the northeastern Tibetan Plateau. We tied the InSAR LOS (Line of Sight) velocity to the stable Eurasian reference frame adopted by GNSS. Using Kriging interpolation constrained by GNSS north–south components, we decomposed the ascending and descending InSAR velocities into east–west and vertical components to derive a high-resolution 3D deformation. We found that a sharp velocity gradient extending ~45 km along the strike of the Laohushan segment, with a differential movement of ~3 mm/a across the fault, manifests in the east–west velocity component, suggesting that shallow creep has propagated to the surface. However, the east–west velocity component did not exhibit an abrupt discontinuity in the rupture zone of the Haiyuan earthquake. Subsidence caused by anthropogenic and hydrological processes in the region, such as groundwater extraction, coal mining, and hydrologic effects, exhibited distinct distribution characteristics in the vertical velocity component. Our study provides valuable insights into the crustal movement in this region.

In the early stages, uncontrolled groundwater extraction led to the Hangjiahu (HJH) Plain becoming one of the areas with the most severe land subsidence in China. Since the beginning of this century, comprehensive measures have been taken to control the continuous aggravation of large land subsidence patterns in some areas; however, urban land subsidence issues, influenced by various factors, still persist and exhibit complex geographical distribution characteristics. In this study, we utilized Sentinel-1A images and the SBAS-InSAR technique to capture surface deformation over the HJH Plain in Zhejiang from 16 March 2017 to 20 January 2023. Through a comparative analysis with geological conditions, changes in surface mass loading, rainfall and groundwater, and land use types, we discussed the contributions of natural and anthropogenic factors to land subsidence. Augmented with optical remote sensing images and field investigations, we conducted a correlation analysis of the land subsidence status. The preliminary findings suggest that changes in surface mass loading and short-term heavy rainfall under extreme weather conditions can lead to periodic land subsidence changes in the region. Additionally, extensive infrastructure construction triggered by urbanization has resulted in significant and sustained land subsidence deformation. The research findings play an important guiding role in formulating scientifically effective strategies for land subsidence prevention and control, as well as urban planning and construction.

We have calculated the deformation velocity field for the Makran subduction and North Tibet region with the spatial range of [25°N - 31°N; 55°E-67°E] and [30N°-41°N; 85°E-97°E], respectively. There are two significant deformation signals in the epicenter of the 2013 Mw 7.7 Balochistan earthquake and the 2001 Mw 7.8 Kokoxili earthquake. For the Balochistan earthquake, we found that the 7-year post-seismic deformation was due to the widespread aseismic slip along the megathrust and not due to the viscoelastic relaxation. For the Kokoxili earthquake, we probed whether the viscoelastic relaxation of 2001 Kokoxili earthquake is still continuing. We first simulate the deformation caused by the interseismic slip along the major active faults in Tibet. By comparing the simulated deformation and the observed deformation, we found the maximum ratio of the simulated deformation to the observation is 42%, which means that the viscoelastic relaxation of 2001 Kokoxili earthquake is still continuing. The effective viscosities of lower crust and upper mantle are inverted as 1.78*1019Pas and 1.78 * 1020Pas, respectively.