关键词: 古冶Ms5.1地震, 地电阻率, 地电场, 极低频, 电磁异常

Abstract: In this study, the data of geo-electric resistivity, geo-electric field, and extremely low frequency(ELF) observation within 400km of the Guye Ms5.1 earthquake on July 12th, 2020, is analyzed using a combination of time-domain waveform analysis, sliding Fourier subtract annual variation analysis, normalized variation rate method(NVRM), and geo-electric azimuthal method. After eliminating the influencing factors such as operation status, observational environment, and the spatially electromagnetic effect, we consider that 6 geo-electric resistivity stations exhibit a variation of “trend decrease--accelerated decrease--postseismic recovery” and 7 stations with a threshold value of the normalized variation rate exceeding±2.4 within one year before the earthquake. In Luan county, the intensity of the geoelectric field in north-south and north-western directions decrease and then rise back prior to the earthquake. In addition, the azimuth shifts to the direction of the Guye earthquake in the preseismic period, and then returns to the direction of the Luan-Leting fault. The ELF stations in Wen’an and Fengning has precisely recorded the coseismic change of the 16Hz natural magnetic field, in which the variation of the vertical component is twice larger than that of the horizontal component. Under the condition of large subsurface structure difference beneath the stations, the observed electric values from the two stations are distinctively different; moreover, the coseismic disturbance is submerged by the background noise. By inversing the data collected from the ELF stations in the capital area, the subsurface electric structure is obtained. The structure indicates that Guye earthquake occurs near the boundary where the electric property changes. Meanwhile, it shows high electric resistivity in northern areas, low electric resistivity in southwestern areas, and partially low electric resisitivity in Baodi and Wen’an. Further, the characteristics of the electromagnetic phenomenon of Guye earthquake are preliminarily analyzed. With regard to the problem of anomalously spatial selectivity, we believe it may be related to the two main conjugated structure directions in the capital area, which lie in NEE and NW, respectively. Finally, the study also enlighten researchers that the investigation of the mechanism of seismic electromagnetic anomaly should be started from the coseismic phenomenon, and then deepened through the aspect of seismic signal source and propagation path.

Key words: Guye Ms5.1 earthquake, georesistivity, geoelectricity field, extremely low frequency(ELF), electromagnetic anomaly