## 1 Introduction  
Previous studies on geomagnetic numerical simulations have shown that in magnetic field signals with frequency bands of 10\({}^{-2}\)\(\sim\)10\({}^{2}\) Hz, the amplitude of the vertical component of the primary source from the magnetic signal inside the crust observed at the surface is greater than or close to the amplitude of the horizontal component (e.g., [1]). The ratio of the amplitude of the vertical component to the horizontal component of the magnetic field from the Earth's crust is greater than or close to one. However, based on electromagnetic induction theory, the ratio of the amplitude of the vertical component to the horizontal component of the magnetic signal from the outer space of the ionosphere is less than one. [PERSON] et al. [2] developed the method of geomagnetic vertical intensity polarization (GVIP) to extract the high amplitude ratio of the geomagnetic vertical component to the horizontal component and obtain the magnetic field signal from the subsurface. By analyzing the changes in polarization values before and after the Mw 8.0 earthquake in Guam on 8 August 1993, and using magnetic fluxgate magnetometer observations at the Guam Geomagnetic Station, which is located 65 km away from Guam, studies found that the polarization value in the 0.01-0.05 Hz (100-20 s) band gradually increased in the two months before the earthquake, reaching a maximum at the time of the earthquake, and gradually recovered after the earthquake (e.g., [2]). Numerous seismic events have since been identified anomalously through high polarization values in the days to three months prior to the earthquake (e.g., [3; 4; 5; 6; 7]). [PERSON] et al. [8] subjected the polarization results to a more refined frequency segmentation, and more significant anomalous signals of polarization values were extracted in the frequency bands of 0.02-0.022 Hz (50-45 s) and 0.05-0.1 Hz (20-10 s) before the 1997 Guam Mw 8.0 earthquake and the 2000 Izu swarm earthquakes. Based on fluctuation theory, a three-dimensional anomalous body model was constructed, and the seismic geomagnetic disturbance signal coinciding with the anomalous polarization value was obtained by numerical simulation (e.g., [8]). [PERSON] et al. [9] found that geomagnetic vertical intensity polarization has an annual variation characteristic and eliminated it before extracting the high value of the polarization anomaly. The high value of the polarization anomaly at the Kashi station after eliminating the annual variation corresponds well to the earthquakes around the station that occur 2 months after it, with most of the earthquakes occurring within 1 month [9]. Although some earthquake predictions have been obtained by the GVIP anomaly method, the reliability of this method for extracting information on seismic geomagnetic anomalies is still unknown. First, selecting data at midnight does not fully prevent the influence of the magnetospheric current system on the elevated polarization values, even though many studies have demonstrated that high polarization values are negatively correlated with the geomagnetic activity index (e.g., [9; 10; 11; 12; 13]). Second, due to the limitations of station observation data quality and station spacing, pre-seismic anomalies usually exist only at the single station with the closest epicenter, and the reliability of pre-seismic anomalies is often questioned when data interference cannot be excluded. However, based on the small-aperture array observation data established in northwest Yunnan, [PERSON] et al. [12] extracted the pre-seismic polarization anomalies at several stations using the polarization method. Their results showed that the polarization values of each station had abnormally high fluctuations half a month before the earthquakes occurred and returned to normal one week before the earthquake, and the amplitude of the anomalies gradually decreased with increasing distance from the epicenter, which was consistent with the attenuation characteristics of seismic electromagnetic disturbance signals (e.g., [14]).