[S-GD03] 地殻変動

[SGD03-P10] Estimated Seismic Source Parameters for 2020 M_W 5.6 Dingri, Southern Tibetan Plateau Earthquake and Study on the Stress Triggering

*Qi Li¹ (1.Institute of Seismology, China Earthquake Administration)

キーワード： InSAR deformation, slip distribution, Nepal earthquake, Dingri earthquake

The 20 March 2020 M_W 5.6 Dingri earthquake occurred in the southwestern margin of the Tibetan Plateau, about 250 km away from the 2015 Nepal M_W 7.9 earthquake. Whether the Nepal earthquake triggered the Dingri earthquake remains to be studied. Because the rough focal mechanism solutions and source locations based on seismic wave data reported by several institutes are different, they cannot be used to create a reliable fault model for inverting the slip distribution. Here, Interferometric Synthetic Aperture Radar and regional seismic data were combined to learn about the rupture features of the Dingri earthquake. We first utilized the near-field displacements together with 15 broadband seismic waveforms to reveal the uniform slip model by using a Bayesian bootstrap optimization nonlinear inversion method. Then, we created a fault plane based on the geometrical parameters and inverted the slip distribution. Analysis of the data based on a finite fault model indicates that the coseismic slip occurred on a subsurface plane of 5.6 km × 4.4 km in size with a dip of ~ 51° to the east and a strike of ~ 334°. The peak slip was ~ 1.27 m, which occurred at a depth of ~ 3.786 km. The earthquake released a seismic moment of ~ 3.33 × 10¹⁷ N·m, corresponding to M_W 5.6. The slip was mainly confined between ~ 2.0 and 5.5 km in depth and was characterized predominantly by normal slip with slight right-lateral strike-slip components, which suggested that the Indian plate compresses the Eurasian plate northeastward, which produces near East-West tension in southern Tibet Plateau. The study of Coulomb stress change shown that the Nepal M_W 7.9 earthquake and its aftershocks, together with four historical earthquakes in Dingri area, triggered the 2020 Dingri M_W 5.6 earthquake. The Coulomb stress change caused by afterslip in two years of the Nepal earthquake accounts for ~ 40%, which indicates that the role of the afterslip in seismic risk assessment cannot be ignored.