Investigation of earthquake precursors using magnetometric stations in Japan

Earthquakes are one of the most devastating natural disasters, and their impact on human society, in terms of casualties and economic damage, has been significant throughout history. Earthquake prediction can aid in preparing for this major event, and its purpose is to identify earthquake-prone areas and reduce their financial and human losses. Any parameter that changes before the earthquake in a way that one can predict the earthquake with a careful study of its variations is called a precursor. Recently, more attention has been paid to geophysical, geomagnetic, geoelectrical, and electromagnetic precursors. In the present study, the geomagnetic data of three stations, obtained through INTERMAGNET, with a distance of less than 500 km to the 5 Sep. Japan earthquake are investigated. Then the method of characteristic curves is used to remove the effect of diurnal variation of the geomagnetic field. After that, by examining the anomalies which are more distinct after implementation of the method, the cases are matched with the seismic activities of the region. By separating the noise from the desired signal, a pure anomaly can be observed. Among the various magnetic components, the horizontal components are more suitable than the others for the proposed process because of more variations in the geomagnetic field in the vertical direction due to the presence of the geomagnetic gradient. In the present study, one year of magnetic data, including three stations and for X, Y, and Z components, and seismic data for Japan are used to implement this method. The method is based on plotting different magnetic field components in specific time intervals in the same 24 hours frame. This will lead to a plot which shows the geomagnetic nature of each component of the geomagnetic field for each station After averaging the values for every point at the horizontal axis of the plot, which is a unit of time depending on the sampling (hourly mean, minute mean, etc.) a curve will be obtained which is called the characteristic curve. Then we reduce the characteristic curve values from geomagnetic data to reveal the anomalies, free of diurnal variation noise so that the possible anomalies related to earthquakes will be shown more distinctly. After drawing the components of the magnetic field and removing the daily changes from each of the components, we can observe the anomalies related to the earthquakes to justify the observed anomalies better and considering the standard deviation for each component, pre-seismic anomalies have a more significant distinction than the original data for being studied as a seismic precursor. After all, further investigation revealed the presence of a magnetic storm during the time period under investigation. This led to uncertainty in the feasibility of using the geomagnetic data in the present study as a precursor. However, several other pieces of evidence confirm the existence of precursory geomagnetic phenomena before earthquakes. Thus based on the current data and results, it is not possible to conclude the applicability of precursory geomagnetic studies and further data and studies are required.