Abstract:
On January 30, 2023, a
MS6.1 earthquake occurred in Xinjiang Shaya in the northern Tarim basin. The
MS6.0 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
MS6.1 Shaya earthquake and 2012
MS6.0 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 results indicate that the 2023
MS6.1 Shaya earthquake is a strike-slip event with strike, dip, rake of 251°, 68°, 6° and 159°, 84°, 158° for nodal planes Ⅰ and Ⅱ respectively, for which the P-axis azimuth is 207° and plunge angle is 11°, and that of the 2012
MS6.0 Luopu earthquake is a thrust event with strike, dip, rake of 274°, 61°, 67° and 135°, 36°, 125° for nodal planes Ⅰ and Ⅱ respectively, for which the P-axis azimuth is 20° and plunge angle is 13°. The P axis azimuths both show the consistance 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\subseteq 10
17 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\subseteq 10
17 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 sliding angle 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 existing studies, it is speculated that the node plane Ⅱ of the focal mechanism 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 maybe 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 strike and SW dip 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.