Fig. 9

Bouguer gravity anomaly in the Hakodate Plain. a The Bouguer anomaly map drawn utilizing the Gravity database of Japan (GSJ 2013). The assumed density is 2.30 g/cm³. The small dots represent gravity observation points collected in the database. b The theoretical gravity anomaly based on the J-SHIS V2 model (Fujiwara et al. 2012). c The theoretical gravity anomaly map based on the new velocity structure model of this study. The open triangles and open circles indicate the control points for the mictotremor array surveys and the reflection surveys, respectively