Quantitative influence of Pc4 geomagnetic pulsations on geomagnetic polarization analysis

Geomagnetic polarization analysis is a widely utilized geophysical method that plays a critical role in the research of earthquake precursors. However, the lack of comprehensive discussion regarding its applicability has resulted in enduring controversies surrounding its research outcomes. This paper aims to address these controversies. Using continuous geomagnetic pulsations of the Pc4 type as a case study, we quantitatively investigate their influence on polarization analysis results based on data collected from geomagnetic stations across various latitudes in mainland China. Our findings reveal that the impact of Pc4 pulsations on polarization results is significantly influenced by several factors, including the observation component, frequency range, geographic latitude, background noise, and the level of geomagnetic activity. Specifically, we observe that Pc4 pulsations markedly increase the power spectral density (PSD) of the SH, SD, SZ and SG within the corresponding frequency range, while simultaneously decreasing the polarization values YZH and YZG. Furthermore, the influence on SD and YZD intensifies with increasing latitude, whereas the effects on SZ and YZH are more closely related to the background noise levels. Notably, a lower background noise level results in a more pronounced effect on SZ but a diminished effect on YZH. Additionally, the influence of Pc4 pulsations on polarization values is more significant during periods of weaker geomagnetic activity. Based on these findings, we propose several recommendations for the application of seismo-geomagnetic polarization analysis, specifically concerning the selection of observation components, frequency ranges, and geographic latitudes. This study provide valuable insights for employing the polarization analysis method in earthquake precursor research.