Precursory migration of anomalous seismic activity revealed by the pattern informatics method: A case study of the 2011 Tohoku earthquake, Japan

Anomalous seismicity patterns in epicentral and surrounding areas have been shown to occur prior to large earthquakes, although the processes determining the spatial distribution and migration patterns of such seismicity are still poorly understood. We applied the improved pattern informatics (PI) method to earthquake data maintained by the Japan Meteorological Agency (JMA) for a broad region including northeastern inland Japan and the source area of the 2011 Tohoku earthquake, in order to reveal the precursory processes of the earthquake and its related statistical features. In particular, we focused on the spatial distribution and migration patterns of PI hotspots, which highlight areas of anomalous seismic activity. Our results show that such hotspots had been approaching the epicenter of the 2011 Tohoku earthquake from 2000 until the earthquake occurred. The possibility that this result was obtained by chance was rejected at the 95% confidence level based on Molchan's error diagram. Our result supports the hypothesis that the preparatory processes of the 2011 Tohoku earthquake included anomalous seismic activity and its migration toward the epicenter of the earthquake.