Fig. 4

Bouguer anomaly map for the study area (modified from Geological Survey of Japan, 2013). A density of 2.67 g/cm³ was used for calculating Bouguer anomalies. The contour interval is 2 mGal. The white line shows the coastline. The black dashed rectangle indicates the distributional range of the aftershocks used in the stress tensor inversion by Ohtani and Imanishi (2019). The big double arrows indicate the locations of large-scale N–S-striking structure (Yamamoto 2005). There are many small-scale structures, among which some are shown with small double arrows