Stress and strain characteristics in the seismic region of the M6. 1 Nakchu earthquake on March 19, 2021 and their geodynamic implications

The M6. 1 earthquake occurred on March 19, 2021, in Nakchu, Tibet. Stress-strain environment and stress evolution in the seismic region are of great significance for understanding the background of earthquake preparation and seismogenic mechanism. After the earthquake, we quickly collected stress data and focal mechanism solutions around the epicenter as well as GPS data to perform regional tectonic stress field inversion and strain rate calculation. Based on the dislocation model of historic strong earthquakes, we employed the PSGRN/PSCMP program to calculate the Coulomb stress changes at the epicenter of the M6. 1 earthquake caused by the surrounding strong earthquakes. The preliminary results show that the maximum principal compressive stress axis of the tectonic stress field around the epicenter is NNE trending, which is subparallel to the strike of the seismogenic fault plane, making this earthquake characterized by the dominated normal fault activity. The azimuth of the maximum principal compressive strain rate is consistent with the axis of maximum principal compressive stress, and the earthquake lies in the gradient zone of the maximum shear strain rate. The occurrence of the 1950 M8. 7 Chayu earthquake caused the co- and post-seismic stress changes at the epicenter to increase by 1.9X10(4) Pa and 8.27X10(4) Pa, respectively. Meanwhile, the cumulative Coulomb stress change at the epicenter caused by the nine historic strong earthquakes since the M7(2)/(3) southern Damxung earthquake in 1411 increased by 9.06X10(4) Pa, indicating that the M6. 1 Nakchu earthquake occurred in a context of the continuous convergence between the Indian and Eurasian plates, and the regional historic strong earthquakes promote its occurrence. This study provides a theoretical basis for understanding the seismogenic background and dynamics of the Nakchu earthquake.