ULF geomagnetic anomalous changes related to large earthquakes: Case and statistical studies

In order to verify and clarify the ULF seismo-magnetic phenomena, a statistical investigation of the relation between magnetic anomalies and local seismicity has been performed. Geomagnetic data observed during 2001~2010 at the Kakioka observation (JMA), Izu and Boso stations have been analyzed. Energy of ULF geomagnetic signals at the frequency around 0.01Hz has been investigated by wavelet transform analysis. To identify anomalous changes induced by ionospheric disturbances, the adequate station has been chosen as a reference station. Statistical studies by superposed epoch analysis (SEA) have indicated that before a sizeable earthquake there are clearly higher probabilities of ULF anomalies than that after the earthquake: statistical results of daily counts were found significant, which suggests a correlation between ULF geomagnetic anomalies and local seismicity.