[M-IS04] Interdisciplinary studies on pre-earthquake processes

[MIS04-P01] Statistical analysis and Evaluation of ULF seismo-magnetic phenomena at Kakioka, Japan, during 1983-2017

*Kei Takahashi¹, Katsumi Hattori², Peng Han³ (1.Faculty of Science, Chiba University, 2.Graduate School of Science, Chiba University, 3.Southern University of Science and Technology, China)

To clarify and verify the ultralow frequency (ULF) seismo-magnetic phenomena, we have performed statistical studies on the geomagnetic data observed at the Kakioka (KAK) station, Japan, during 1983-2017. We investigated the energy of ULF geomagnetic signals of the frequency around 0.01 Hz using wavelet transform analysis. To minimize the influences of artificial noises and global magnetic perturbations, we used only the geomagnetic data observed at midnight time (LT 2:30 A.M. to 4:00 A.M.).We define the geomagnetic anomalies when the Z components of geomagnetic data exceeds median + 1.5 IQR, where IQR is the interquartile range. Considering that ionospheric disturbances may also lead to enhancements in the Z component, we exclude the anomaly when the energy of H component exceeds median + 3.0 IQR. Statistical analysis of superposed epoch analysis have indicated that ULF magnetic anomalies are more likely to appear before sizable isolated earthquake events (Es parameter which is higher than 8th power of 10 and no earthquake events during ±45 days ) rather than after them, especially 6-10 days before the events. Finally, we have evaluated the precursory information of ULF geomagnetic signals for local sizable earthquakes using Molchan’s error diagram. The above results have indicated that the ULF seismo-magnetic phenomena at Kakioka clearly contain precursory information and have a possibility of improving forecasting of large earthquakes.