Principal component analysis of geomagnetic diurnal variation associated with earthquakes:case study of the M6.1 Iwate-ken Nairiku Hokubu earthquake

This study provides a new seismomagnetic data processing method by combining principal component analysis (PCA) and geomagnetic diurnal variation analysis.As a case study, we investigated the geomagnetic data observed at Matsukawa,Kakioka,and Memambetsu stations and discussed their relationship with the M6.1 Iwate-ken Nairiku Hokubu earthquake occurred in 1998.The results showed that there is a clear anomaly of the geomagnetic diurnal variations about two weeks before the mainshock at Matsukawa station,which is only 15 km away from the epicenter.After applying the PCA method to the geomagnetic diurnal data,we investigated the temporal variations of the contribution of each principal component.The results indicated that the contribution of the 2~(nd) principal components,which may relate with the local underground conductivity structure and/or the local electromagnetic disturbance possibly due to the local seismogenic process,increased significantly about two weeks before the earthquake. These results are consistent with those obtained independently from the previous case studies by using polarization analysis method.This study may strengthen the understanding of seismoelectromagnetic phenomena.