Abnormal variation of dominant azimuth and load/unload response ratio of geoelectric field before the Menyuan MS6.9 earthquake

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    An MS6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. Based on the observation data of the electric field within 300 km of the epicenter in recent 5 years, 9 observation stations were analyzed and selected. According to the seepage (movement) model of rock fissure water (charge), the dominant azimuth of the geoelectric field was calculated. The loading and unloading response ratio (LURR) value of the geoelectric field was calculated through the LURR calculation method of Coulomb stress-triggered model. The results showed that: (1) The stations with geoelectric field anomalies calculated by the two different methods are consistent in spatial distribution. Among them, the dominant azimuth and LURR of the geoelectric field at Gufeng, Huangyangchuan, Sitan, and Lanzhou stations showed abnormal changes before the earthquake, while those at Shandan and other stations did not show obvious anomalies. (2) The time series changes of Lanzhou and Sitan stations using the two calculation methods are consistent, showing quasi synchronization. Combined with the focal mechanism solution, the correlation between the dominant azimuth of abnormal stations and the principal compressive stress P-axis direction was analyzed, and the results basically conform to the petrophysics theory. The two calculation methods of geoelectric field dominant azimuth and LURR value are related in mechanism, and a comprehensive analysis of their abnormal evolution characteristics may help to further understand the physical process of earthquake preparation.

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  • Online: April 07,2022
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