Remarkable variations in geomagnetic disturbances preceding the 2017 M 7.1 Jiuzhaigou earthquake

With the rapid development of geomagnetic observation networks and the increased availability of geomagnetic data in China over the past decade, multistation geomagnetic data analyses have become widely used in studies of earthquake precursors with magnitudes >6. Building on the single-station polarization algorithm, we propose a multistation daily sliding polarization correlation algorithm for detecting regional geomagnetic anomalies. This method can be applied to analyze the spatiotemporal evolution of geomagnetic field anomalies that are related to seismogenic processes before major earthquakes. In this study, we calculate polarization correlation time series data before and after the 2017 M 7.1 Jiuzhaigou earthquake. The results show that following the appearance of polarization anomalies, the regional correlations increase, then decrease, and subsequently increase again. Earthquakes occurred at the inflection points of these correlation trends. Our analysis suggests that changes in multistation polarization correlations directly reflect regional geomagnetic field anomalies that are caused by tectonic activity, thereby capturing the dynamic evolution during earthquake preparation. This method offers valuable insights into the mechanisms linking geomagnetic polarization anomalies with seismic events.