Changes of apparent resistivity before the 2022 Ms 6.9 Menyuan，Qinghai earthquake revealed by fault virtual dislocation model

A major earthquake (Ms 6.9) struck the Menyuan county of Haibei prefecture, Qinghai Province, China. There are nine apparent resistivity observation stations within 400km of the epicenter. In this study, observation data with high quality and stable annual variation was selected to extract anomalies by removing the normal annual dynamics under the influence of soil water and soil temperature. The results show that the EW direction at Jinyintan station, the NS and EW direction at Wuwei station, and the EW and N45°W direction at Shandan station were found anomalies and exhibit anisotropic characteristics. According to the fault virtual dislocation model, a negative anomaly was found in EW direction of Jinyintan station, which is located in the pre-earthquake compression zone. Meanwhile, the NS direction of Wuwei station also showed mainly negative anomalies in the early stages of the earthquake preparation, but a normal anomalies was demonstrated in the late phase of strong earthquake preparation, while the EW direction shows a normal anomalies in the impending earthquake stage; A positive anomaly was observed with the EW direction of Shandan station one year prior to the apparent earthquake, and the array of N45°W direction has continued to be quite positive since August 2020, and exceeding the threshold value in August. The NS direction of Dingxi station is also in the expansion zone, and it is close to the abnormal threshold from September to November ,2020. In accordance with the experimental results and theoretical models, the temporal and spatial characteristics of the variation of apparent resistivity before the M_s6.9 Menyuan earthquake are consistent with the accumulation of stress-strain in the epicenter and gradual attenuation toward the periphery. Therefore, the spatio-temporal variation of apparent resistivity before the M_s6.9 Menyuan earthquake may be related to regional medium deformation and stress state.