An Improved Source Model of the 2021 Mw 6.1 Yangbi Earthquake (Southwest China) Based on InSAR and BOI Datasets

Abstract

The azimuth displacement derived by pixel offset tracking (POT) or multiple aperture InSAR (MAI) measurements is usually used to characterize the north-south coseismic deformation caused by large earthquakes (M > 6.5), but its application in the source parameter inversion of moderate-magnitude earthquakes (~M 6.0) is rare due to the insensitive observation accuracy. Conventional line-of-sight (LOS) displacements derived by the Interferometric Synthetic Aperture Radar (InSAR) have limited ability to constrain the source parameters of the earthquake with near north-south striking. On 21 May 2021, an Mw 6.1 near north-south striking earthquake occurred in Yangbi County, Yunnan Province, China. In this study, we derive both the coseismic LOS displacement and the burst overlap interferometry (BOI) displacement from the Sentinel-1 data to constrain the source model of this event. We construct a single-segment fault geometry and estimate the coseismic slip distribution by inverting the derived LOS and BOI-derived azimuth displacements. Inversion results show that adding the BOI-derived azimuth displacements to source modeling can improve the resolution of the slip model by ~15% compared with using the LOS displacements only. The coseismic slip is mainly distributed 2 to 11 km deep, with a maximum slip of approximately 1.1 m. Coulomb stress calculation shows a maximum Coulomb stress increment of ~0.05 Mpa at the north-central sub-region of the Red River Fault. In addition, there is a small Coulomb stress increase at the Southern end of the Weixi-Weishan fault. The potential seismic risks on the Weixi-Weishan and Northwest section of the Red River faults should be continuously monitored.

Crustal structure and the seismogenic environment in Yunnan imaged by double-difference tomography

“…Figure 13 shows that the center of the Yangbi earthquake is located in the boundary of high-and low-Vp anomalies, which is consistent with the result of Lv et al (2022) and Hu et al (2021). The relocation of the Ms 6.4 Yangbi earthquake sequence shows that the sequence is about 3-13 km away from the nearest known Weixi-Qiaohou fault (Figure 13D), (Li et al, 2022;Lu et al, 2022), indicating that the Yangbi earthquake occurred in the shallow area of the upper crust (Long et al, 2021). Meanwhile, the stress transmitted into the surrounding tectonics caused by the Yangbi earthquake affects the magnitude of Coulomb stress in the southeastern section of the Weixi-Qiaohou fault, significantly increasing the stress in this fracture zone.…”