Imaging the high b-value anomalies within the subducting Pacific plate in the Hokkaido corner

The frequency-magnitude distribution (b-value) for seismicity within the Pacific plate is not definitely homogeneous. An anomaly of b-value higher than 0.9 is detected within the descending Pacific plate in the Hokkaido corner. In the western Hokkaido, the anomaly exists at a depth of about 150 km, which is directly beneath active volcanoes. In the eastern Hokkaido, the anomalies exist at approximately 200 and 300 km depths, which is tens of kilometers sideways from active volcanoes. The results obtained in this paper are more reliable than previous studies on b-value heterogeneity within descending plates, since I used a catalog homogeneous, both in time and space, which was obtained through re-examination of all seismograms and relocation of hypocentral parameters based on arrival times from fixed seismic stations.