Research on the characteristics of the Maerkang MS6.0 earthquake based on the joint analysis of annual changes in gravity and magnetic fields

Abstract

Using multi-period ground gravity and geomagnetic observation data from 2017 to 2021 in western Sichuan, the MS6.0 earthquake in Maerkang was analyzed. The results from the annual variation normalization fusion analysis of gravity and magnetic fields were applied to study the seismic location of the earthquake. A correlation between these fusion analysis results and elements of the Maerkang earthquake was established. The findings indicate that regional gravity field anomalies are closely related to fault zones in western Sichuan. In the epicentral area of the Maerkang earthquake, gravity field changes were relatively weak, with the change contour consistently near the zero line, while surrounding areas experienced significant change. The annual variation of the lithospheric magnetic field revealed that the horizontal vector of the magnetic field weakened overall before the earthquake, with the epicentral region continuing to weaken and the periphery converging, followed by a reverse weakening. The weak variations were small in magnitude and directionally scattered. By integrating normalized annual variation data of gravity and magnetic fields from the year before the earthquake, the interval range for strong earthquake occurrence was determined based on the overlap of the kernel density curve and the condition of small peak differences (30°N～33°N, 101°E～104°E). Notably, the MS6.1 Lushan earthquake and the MS6.0 Maerkang earthquake both occurred within this interval range in June 2022. After dividing the western Sichuan region into 1°×1° grids, it was found that the peak difference in the gravity and magnetic variation kernel density curve in the Maerkang area decreased year by year, reaching its minimum before the earthquake. The changes in magnetic susceptibility of both the gravity and lithospheric magnetic fields in the Maerkang region showed year-to-year consistency during the seismogenic process. This consistency suggests the exchange and dynamic interaction of matter and energy within the region, leading to material changes and structural deformation of active faults, which in turn caused corresponding changes in the gravity and magnetic fields in the lithosphere. The fusion analysis of annual variations in gravity and magnetic fields offers valuable guidance for determining the locations of strong earthquakes.

Keywords

• gravity anomaly
• normalization
• kernel density curve
• total strength of lithospheric magnetic field