Moment tensor inversion and source fault determination of the 2023 M_S6.1 Shaya earthquake and the 2012 M_S6.0 Luopu earthquake

On January 30, 2023, a M_S6.1 earthquake occurred in Xinjiang Shaya in the northern Tarim basin. The M_S6.0 Luopu earthquake on March 9, 2012 was the latest strong earthquake near the Shaya epicenter. These two earthquakes both occurred in the Bachu uplift to Awati depression tectonic belt. The moment tensor solutions of 2023 M_S6.1 Shaya earthquake and 2012 M_S6.0 Luopu earthquake were determined by gCAP method. The relationship between focal mechanisms of Shaya and Luopu earthquakes and regional stress regime was analyzed. Finally, the source faults were preliminarily determined. Moment tensor inversion results indicate that the 2023 M_S6.1 Shaya earthquake is a strike-slip event with strike 251°, dip 68°, rake 6° for nodal plane Ⅰ and 159°, 84°, 158° for nodal plane Ⅱ, respectively, the Paxis azimuth is 207° and plunge angle is 11°, and that of the 2012 M_S6.0 Luopu earthquake is a thrust event with strike 274°, dip 61°, rake 67° for nodal plane Ⅰ and 135°, 36°, 125° for nodal plane Ⅱ, respectively, the P-axis azimuth is 20° and plunge angle is 13°. The P-axis azimuths are both consistant with the principal compressive stress direction in the NNE direction of the tectonic stress field in the Bachu uplift to Awati depression belt. The results of the full moment tensor solutions show that for Shaya earthquake the seismic moment M₀ is 7.798×10¹⁷ N·m while the moment tensor solutions M_rr, M_tt, M_pp, M_rt, M_rp, M_tp are −0.081, −0.821, 0.342, 0.064, −0.358, 0.685, and for Luopu earthquake the seismic moment M₀ is 9.076×10¹⁷ N·m while the moment tensor solutions M_rr, M_tt, M_pp, M_rt, M_rp, M_tp are 0.517, −0.910, −0.353, −0.491, −0.180, 0.341, and that both Shaya and Luopu earthquakes belong to typical natural tectonic seismic events. The relationship between the focal mechanisms and the stress regime of the two earthquakes reveals that the relative shear stress of the focal mechanism plane is almost the maximum, and the difference between the rake of the focal mechanism and that of the shear stress is small, indicating that the two earthquakes almost both occurred at the optimal release plane of the tectonic stress field, and are mainly affected by the shear stress. Combined with the previous studies, it is speculated that the nodal plane Ⅱ of the focal mechanism solution of the two earthquakes is the possible seismogenic rupture plane. The seismogenic structure of the 2023 Shaya earthquake may be a high-dip transition tear fault on the NW strike above the 30 km deep detachment tectonic belt of the middle crust of Awati depression, and the earthquake dislocation mode may be right-lateral strike-slip. It belongs to the tearing between NW trending translational fault blocks caused by deep subduction from the northern Tarim Craton to the southern Tianshan tectonic belt. The 2012 Luopu earthquake may be related to the NW striking and SW dipping seismogenic fault generated by the overthrust of the hanging wall of Bachu uplift which is in the NE direction above the footwall of Awati depression.