Detection of Geomagnetic Signals as Precursors to Some Earthquakes in China

Abstract

Extracting weak seismic-magnetic signals from strong electromagnetic backgrounds has always been an important part of seismic-electromagnetic research. Based on the data of D/H/Z components measured through a three-axis ring-core-type fluxgate magnetometer in GLM (Geermu), JYG (Jiayuguan), and KSH (Kashi) observatories, we analyzed geomagnetic signals as precursors to some earthquakes in China using the polarization method. The most effective main frequency of seismic-electromagnetic emission was determined according to the skin effect. The results showed that only 5 out of 37 earthquakes were found to have probable signals of seismomagnetic anomalies before them. Further research revealed that the significant enhancements of polarization ratios of YZH and YZG (YZH, the spectral power ratio of Z to H and YZG, the spectral power ratio of Z to G) occurred five days prior to the Jinta earthquake (Ms5.4) and continued for about two months. The polarization ratio of YZH reached an abnormally high value about one month before some earthquakes (Ms7.4, Ms6.7, Ms6.7) near the KSH station and lasted for about one week to half a month, then returned to the normal value. Similarly, some enhancements of polarization ratios of YZH and YZG occurred two months before the Haixi earthquake (Ms5.0) and lasted for about one month. Analysis results showed that the enhancements prior to earthquake events may be closely related to the Jinta earthquake and a series of earthquakes near the KSH station; however, the high value of YZH and YZG in GLM station had nothing to do with the Haixi earthquake.

Anomalous geomagnetic activities before the Karangasem - Bali, Indonesia earthquakes on December 13, 2022

“…In addition, this study is remarkably similar to an earlier study, which discovered that earthquakes with the relationship M ≥ 0.011R + 4.175 will exhibit geomagnetic anomalies prior to their occurrence. This relationship is based on a statistical analysis of 37 M ≥ 5 earthquakes observed in China from 2008 to 2017 [24].…”

Assessment of Ultra-Low Frequency (Ulf) Geomagnetic Phenomena Associated With Earthquakes in the Western Part of Java Island, Indonesia During 2020

“…The EQ preparation process is correlated with the induced magnetic field, which reflects changes in the electrical structure. However, it has a weak intensity and is usually combined with environmental disturbance and external geomagnetic variation (Yao et al, 2022). In the EQ precursor studies, the use of ULF (0.01-0.1 Hz) data could prevent the external geomagnetic variation produced by lightning discharge and ionospheric heating radiation from interfering with EQ precursor analysis (Yusof et al, 2021).…”

“…. This is due to the low attenuation and deep penetration capability of the ULF geomagnetic signal (Han et al, 2014;Yusof et al, 2021;Yao et al, 2022). Assessment of EQ precursors using the geomagnetic method has also been developed in Indonesia for EQs with Mw ≥ 5 (Febriani et al, 2014(Febriani et al, , 2020Ramadhani et al, 2019;Sokacana et al, 2019;Dewi et al, 2020Dewi et al, , 2022Marzuki et al, 2022).…”

Nonlinear Statistical Features of the Seismicity in the Subduction Zone of Tehuantepec Isthmus, Southern México

“…The subduction mechanism could be explained as a complex dynamical system, and then attending to what the SOC theory [2] explains, the possibility of predicting earthquakes is scarce (see also [20]). Nevertheless, there are numerous published works dealing on the possibility of statistically identifying precursory signals associated with earthquakes; these signals are associated with the state of stress of the area where a rupture will occur, and they can be linked to changes in the electric and magnetic fields of the subsoil [21][22][23][24][25]; analyses in natural-time of data series in particular have been very successful in such characterizations [24]. The same type of analysis has been used for the characterization of data point processes such as earthquakes, which has allowed the use of the nowcasting method to assess the risk level of an earthquake that exceeds a given magnitude.…”