Abstract：Based on the mobile geomagnetic observation data of four consecutive periods from 2020 to 2023 in the border area of Hebei and Shandong, this paper analyzes the temporal and spatial variation characteristics of the regional lithospheric magnetic field and its relationship with the Pingyuan MS5.5
earthquake on August 6, 2023. Combined with the laboratory results of rock magnetism and the theory of fault meta-instability, it discusses the meta-instability characteristics before the plain earthquake and the seismogenic mechanism.The results show that:1) The spatial and temporal variation characteristics of the lithospheric magnetic field in the study area have obvious anomalies before the Pingyuan MS5.5 earthquake. There is always a weakening area of the horizontal vector near the epicentre from 2020 to 2023, and with the passage of time, the weakening area with horizontal vector gradually approaches the epicentre; there is always a 0 value line of the total geomagnetic intensity, magnetic declination and vertical component near the epicentre. 2)The time series variation of the observation points near the epicentre in 2020-2021 is highly consistent, which better reflects the synergistic activity state of the faults near the observation points, and may be used as one of the characteristics to identify the sub-instability stage of the faults.3) By analyzing the relationship between stress and magnetic field intensity, it can be seen that the total intensity of geomagnetic field in the middle and eastern segment of Linnan fault and the north-eastern segment of Liaocheng-Lankao fault increases, and the crustal stress should be in a release state; the total intensity of geomagnetic field in the western segment of Linnan fault and Tangyi fault decreases, and the crustal stress should be in an accumulation state. The stress release of the former can promote the stress accumulation of the latter, which may lead to the instantaneous increase of the shear stress of the latter and instability when it exceeds its strength, thus triggering the plain earthquake.
ZHANG Haiyang. Abnormal Variation of Lithospheric Magnetic Field before the Pingyuan MS5.5 Earthquake in Shandong Province and Its Seismogenic Mechanism[J]. jgg, 2024, 44(9): 892-898.
