InSAR coseismic deformation field and tectonic implications of the 2023 MS 5.5 Subei Earthquake, Gansu, China

Objective On October 24, 2023, an MS 5.5 earthquake occurred in Subei County, Jiuquan City, Gansu Province. The epicenter was located in the Qilian mountain seismic belt at the northeastern margin of the Qinghai-Tibet Plateau. Understanding the seismogenic mechanism of this earthquake and its relationship with the tectonic stress field is crucial for analyzing the seismic hazard in the region. Methods The InSAR coseismic deformation field of the MS5.5 earthquake in Subei was obtained using ascending and descending Sentinel-1 SAR data, and the parameters of the seismogenic fault were determined based on a uniform slip model. Subsequently, a distributed slip inversion method was applied to obtain a detailed slip distribution of the seismogenic fault. Furthermore, the earthquake-induced changes in the Coulomb stress and the regional interseismic strain rate were determined. Results The results indicate that the surface deformation values generated by this earthquake reached 12 cm and 9 cm in the ascending and descending InSAR line of sight, respectively. The deformation primarily manifests as surface uplift; the seismogenic fault is a concealed fault located between the Shule Nanshan Fault and the northern margin fault of the Central Qilian, the strike is approximately 166.97°, the dip angle is around 68.69°, and the slip angle is about 110.39°; the fault slip is primarily concentrated within the depth range of 1.2 km to 4.9 km, with a maximum slip of 0.58 m occurring at a depth of approximately 2.56 km; the moment magnitude obtained from the inversion is MW 5.6, and the coseismic rupture is primarily characterized by thrust motion with a minor component of right-lateral strike-slip. This seismic event resulted in regional Coulomb stress changes between the northern margin fault of the Central Qilian and the Shule Nanshan Fault, as well as in the northern area of the Shule River Fault Zone. Additionally, the regional surface strain rate exhibited a distinct compressive trend before the earthquake, with higher surface strain and maximum shear strain rates observed on the northern side of the seismic zone. Conclusion The continuous accumulation of strain leads to an increased seismic hazard, with historical earthquakes often occurring in gradient zones where strain values transition from high to low. Considering the regional strain distribution characteristics and seismic activity, the seismic hazard in this area remains significant in the future and should not be overlooked. [Significance] The research findings have a certain guiding significance for understanding the tectonic background of the Qilian Block and its seismic hazard.