Characteristics and mechanisms of near-surface atmospheric electric field negative anomalies preceding the 5 September, 2022, Ms6.8 Luding earthquake, China
Abstract. A Ms6.8 strike-slip earthquake (EQ) occurred in Luding, Sichuan province, China, on 5 September, 2022, causing great losses to the surrounding Ganzi Prefecture and Ya’an City. In this research, the near-surface atmospheric electric field (AEF), recorded at four discretely distributed sites 15d before the Luding EQ, were analyzed and discriminated by using multi-source auxiliary data including precipitation, cloud base height and low cloud cover, and nine possible seismic AEF anomalies at four sites were obtained preliminarily. Accordingly, surface microwave brightness temperature (MBT), which is very sensitive to the surface dielectrics and closely related to the air ionization, together with surface soil moisture, lithology, and 3D-simulated crustal stress field, was jointly analyzed for confirming the seismic relations of the obtained negative AEF anomalies. The geophysical environment for crustal high-stress concentration, positive charge carriers transfer and surface accumulation was demonstrated to exist and satisfy the conditions of generating locally the negative AEF anomalies. Furthermore, to deal with the spatial disparities in sites and regions with potential atmospheric ionization, the data of near-surface wind field was employed to scrutinize the reliability of the AEF anomalies by comprehensively considering the spatial relationships among surface charges accumulation areas, wind direction and speed, as well as the AEF site. Finally, four negative AEF anomalies were deemed to be closely related to the Luding EQ, and the remaining five anomalies were ruled out. The mechanism of negative AEF anomalies before the Luding EQ were believed to be: positive charge carriers were generated from the underground high stress concentration areas, and then transferred to and accumulated on the ground surface and to ionize the surface air, thus disturbing the aground AEF. This study offers an approach to identify and analyze the seismic AEF anomalies, and is also helpful to study the pre-shocking coupling process between coversphere and atmosphere.
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