Coseismic and postseismic deformation of the 2001 MW7.8 Kunlun Mountain earthquake and its loading effect on the 2021 MW7.3 Madoi earthquake

The Bayan Har block in the north-central Tibetan Plateau has been the main seismic region in west China in recent years, and a series of major earthquakes with M-W > 7.0 have occurred around this block. Its northern boundary, the East Kunlun fault, is an active large-scale fault zone with a total length of similar to 2000 km. The 2001 M(W)7.8 Kunlun Mountain(Hoh Xil)earthquake occurred in the middle segment of the East Kunlun fault(or Kunlun fault), and the M(W)7.3 Madoi earthquake occurred on a secondary fault inside the Bayan Har block, similar to 450 km southeast of the Kunlun Mountain earthquake. The Madoi earthquake challenges the previous long-held view that strong earthquakes are more likely to occur on the boundary faults of the Bayan Har block. This earthquake also provides an opportunity to study the relationship among the boundary faults and secondary faults, and earthquakes triggering within the block. This paper explores the potential relationship between the Kunlun Mountain earthquake and the Madoi earthquake using postseismic InSAR observations and the Coulomb stress change, which are obtained from a large amount of SAR data acquired after the Kunlun Mountain earthquake. The InSAR postseismic deformation shows a widespread asymmetric pattern along the rupture zone, and the deformation width and magnitude of the southern part are significantly larger than the northern one. The deformation width of the southern part reaches 250 km, and the near-field deformation rate reaches > 20 mm center dot a(-1). The decay of displacement rate on the southern part is insignificant, implying that the postseismic deformation forms a enduring eastward loading effect on the Bayan Har block, and will be partitioned into a series of secondary faults inside the block. The stress loading increases the seismic potential of the secondary faults. The interseismic strain map during 2015-2020 shows a high strain rate zone along the secondary fault, the Kunlun Mountain Pass-Jiangcuo fault. We calculate the cumulative Coulomb stress change caused by the coseismic rupture and postseismic processes of the Kunlun Mountain earthquake. The results show that the stress variation on the seismogenic fault of the Madoi earthquake, the Kunlun PassJiangcuo Fault, is significant. Based on these results, we suggest that the coseismic and postseismic deformation of the Kunlun Mountain earthquake may enhance the eastward motion of the Bayan Har block and thus contribute to the occurrence of the Madoi earthquake.