Abstract
During the last 120 years, several large (M>7.5) continental earthquakes (Fig. 1), such as the 1905 Tsetserleg (Mw 7.9)-Bolnay (Mw 8.3) earthquakes and 1957 Mw 8.1 Bogd earthquake, occurred in the East Asia where several important active fault zones exist (e.g. Tibetan Plateau region). Large earthquakes induce a stress change in the ductile lower crust and upper mantle which is relaxed viscoelastically in the years to decades following these events. The viscoelastic relaxation process offers a good opportunity to investigate the rheological structure of the lithosphere. What's more, apparent viscosities are often seen to increase with time since the earthquake. Thus, exploring the viscosities from the 2015 to 2020 post-seismic deformation and combining them with previous studies help us construct the evolution of the regional rheology. Here, we use Sentinel-1 data acquired over ascending and descending orbits during the years 2015-2020 to study the post-seismic deformation for the Bogd earthquake, the Tsetserleg-Bolnay earthquakes and other big (M>7.5) East Asia earthquakes, and explore the lithospheric rheology of these regions. Now, we obtained the LOS displacements from ascending and descending orbits for the Bogd earthquake (Fig. 2a), Tsetserleg-Bolnay earthquakes (Fig. 2b), Manyi earthquake (Fig. 2c) and Balochistan earthquake (Fig. 2d). For the Bogd earthquake, the descending data shows a lobe of up to 1 cm of LOS decrease at the south of the fault. For the Tsetserleg-Bolnay earthquakes, there is a lobe of up to 4 cm of LOS decrease at the southwest of Bolnay fault and the north of fault shows a up to 8 cm of LOS increase. The ascending data for the Manyi earthquake shows an opposite LOS displacement at the both sides of the fault, but there is no significant post-seismic signal for the descending data. For the Balochistan earthquake, the ascending data shows lobes of both LOS increase and decrease (up to 15 cm) and the descending data shows a lobe of up to 10 cm of LOS decrease. Next, we will obtain the post-seismic deformation for other earthquakes (Fig. 1). Then the forward simulations of post-seismic displacements will be generated using RELAX software. Finally, the optimal viscosity values that best fit the observation data from 2015 to 2020 will be solved using a grid search approach among various forward simulations.