Stress field estimation and evaluation in eastern Hokkaido, northernmost Japan

In eastern Hokkaido, a volcanic front extends in the northeast–southwest direction, and small eruptions have occurred in recent years. Although eastern Hokkaido is a low-seismicity region, we estimated the stress field using a larger dataset than those employed previously to understand the stress field in the volcanic region. Furthermore, to assess the validity of the estimated stress field, we conducted: (1) an examination of the reproducibility of the slip direction using the estimated stress field, and (2) a comparison between the estimated horizontal compressional stress direction and the shortening strain direction. Solutions for the focal mechanisms of strike-slip faults are widespread in eastern Hokkaido, Japan. The reverse fault-type focal mechanisms occurred south of the Meakan-dake volcano, and several normal fault-type focal mechanisms occurred in the Kussharo Caldera. The results of the estimated stress field revealed a compressive stress axis aligned with the NW–SE axis in eastern Hokkaido. This compressional stress direction is consistent with the shortening strain direction observed in the GNSS data. The stress field favoring strike-slip faulting was widely distributed in the study area. We also revealed that the presence of a stress field favors reverse faulting around south of Meakan-dake volcano. These estimated stress fields reproduced the slip directions of the focal mechanism solutions that actually occurred in each region. Furthermore, the slip directions of the normal fault-type focal mechanisms within the Kussharo Caldera were reproduced by the estimated strike-slip faults of the stress fields. This indicates that normal faulting is possible under the estimated stress field. Given the presence of multiple active volcanoes near the plate boundary, the detailed stress-field distribution revealed in this study provides important constraints for understanding future seismic and volcanic activity in eastern Hokkaido.