Fig. 12.

Change in Coulomb failure stress (ΔCFS) in, and around, the quiescence and the activation anomalies. The rectangle is a projection onto the ground surface of the assumed fault plane of the LSSE model. (a) ΔCFS at a depth of 60 km. Open black circles indicate the epicenters at depths from 50 to 90 km in the volume of Anomaly 1. The focal mechanism of receiver earthquakes is assumed to be strike = 270°, dip = 20°, and rake = 110°. (b) ΔCFS at a depth of 40 km. Open white circles indicate the epicenters at depths from 0 to 50 km in the volume of Anomaly 2. The focal mechanism of receiver earthquakes is assumed to be strike = 200°, dip = 20°, and rake = 100°. (c) ΔCFS at a depth of 20 km. The white star and black dots show the hypocenter of the 2008 Ibaraki-oki main shock and its aftershocks determined by JMA, respectively. The focal mechanism of receiver earthquakes is assumed to be the same as the 2008 Ibaraki-oki main shock determined by Nagoya University (2008): strike = 205°, dip = 17°, and slip = 87°. (d) and (e) are ΔCFS histograms for earthquakes in the activation and the quiescence areas, respectively. ΔCFSs are calculated based on the focal mechanisms determined by NIED for each earthquake.