A new method for extracting geomagnetic perturbation anomalies preceding the M7.4 Maduo earthquake

Although the single-station geomagnetic polarization method is typically used for predicting impending earthquakes, newly constructed multiple-station geomagnetic networks exhibit more advantages in predicting the exact times and epicenters of events. In this study, the polarization method for extracting geomagnetic radiation anomalies before the M7.4 Maduo earthquake was greatly improved, and mathematical treatments such as normalization and interpolation were carried out via second-sampled observations from multiple geomagnetic stations in western China. In addition, the spatial polarization map was upgraded from the original single-station map to a multiple-station map. The improved spatiotemporal G'-value method can intuitively determine the distribution of anomalies preceding strong earthquakes. Our results showed that (1) two polarization highs occurred near the epicenter 7 months and 15 days before the M7.4 earthquake, and the epicenter was near the core of the high anomaly; (2) the two G" maximum stations are both Qinghai Dulan (DUL) stations, within an epicenter distance of 191 km; the areas of high G"-value zones greater than 0.2 are 58 × 104 km² and 112 × 104 km², respectively. This method provides new insights into identifying seismomagnetic anomalies preceding large earthquake epicenters, which is helpful for in-depth research on characterizing electromagnetic radiation from earthquakes.