Three-dimensional crustal deformation and strain partitioning before the MS 6.9 Qinghai Menyuan earthquake on January 8, 2022

The M(s)6.9 Qinghai Menyuan earthquake, occurred on Jan. 8, 2022, was located in the central to eastern segment of the Qilianshan fault zone. However, the 3D crustal deformation and seismic potential in this region were poorly studied to date. We here determine the fault slip rates and analyze 3D crustal deformation and seismic potential before this event based on the accurate GPS and leveling observations. The results show that, first, crustal deformation in this area is mainly featured by strong shear and contraction, with the latter accommodated by crustal uplift. Second, sinistral, contraction and vertical rates of the Tuolaishan fault are 2. 5 perpendicular to 0. 3 mm circle a (1), 1.3 +/- 0.4 mm circle a (1) and 1.2 +/- 0.6 mm circle a (1), which are larger than those of Minle-Damaying fault of 1.1 +/- 0.3 mm circle a(1), 0.8 +/- 0.3 mm circle a (1), and 0.5 +/- 0.5 mm circle a (1), respectively. The sinistral and contraction rates of the Lenglongling fault are 3.1 +/- 10.7 mm circle a (1) and 3.0 +/- 10. 6 mm circle a (1). Combined with strain rate field, we suggest that upper crust in this region is characterized by distributed deformation. Third, shear and compressional strain in the hypocentral region accumulated significantly before this earthquake, in which part of compressional strain was released by the 2016 M(s)6.9 Menyuan earthquake. While negligible vertical deformation in the south of the Tuolaishan and Lenglongling faults indicate the increase of strain rate. Additionally, GPS velocity profile presents clear interseismic locking along the Tuolaishan fault with a locking depth of 15.0 +/- 7. 8 km, which indicates a high seismic potential.