GEOMAGNETIC DATA AS A PRECURSOR OF THE SEPTEMBER 5, 2018 EARTHQUAKE IN JAPAN (MW= 6.6)

Magnetic anomalies have been discussed long ago as an earthquake precursor. Any parameter that changes before the occurrence of the earthquake, so that a precise investigation of these changes could predict the earthquake, is called a precursor. In this study, the characteristic curves are obtained by frequent over plotting of magnetic data in a 24-hour time frame, for three geomagnetic stations and in Japan (MMB, KAK, KNY). All three components (Z, Y, X) or (Z, D, H) were processed in a period of one year. In order to increase the intensity and distinction of the anomalies observed before the earthquake in comparison with the original data, we tried to eliminate the effect of daily variation of the magnetic field by this method. The changes in the magnetic field associated with the change in stresses were first observed by Stacey (1963) andNagata (1969). Nagata introduced tectonomagnetism for the first time. Tectonomagnetism involves the variation of the magnetic field associated with the occurrence of the earthquake. Reiki Taki (1976) and Melon et al. (1998) studied the geomagnetic effect of earthquakes. Comparison of simultaneous data of a geomagnetic network of seismic magnetic effects is quite evident (Liu et al., 2006). The data are from the INTERMAGNET site and the station's distances are less than 500 kilometers (Figure 1 left).Among the various magnetic components, the X components are usually more suitable for the proposed process. The characteristic curve can be seen in (Figure 1 right), the middle solid line which is surrounded by dash lines which show its uncertainty. After removing daily changes from each of the components, we can observe anomalies related to the earthquakes more distinctly in Figure 2. In this figure, the raw record is presented at left. The processed record at right shows more distinct anomaly prior to the earthquake

Keywords:

Magnetic field , Characteristic curve , Magnetic anomaly , Earthquake