Fig. 2.

(a) Seismographic stations used in the relocation of hypocenters. The rectangle with the bold solid line indicates the study area. Arrival times of P-waves only at the stations indicated by open and closed triangles are used. Arrival times of both P- and S-waves are used at the stations indicated by closed circles. Magnitudes are calculated from the maximum amplitude at the stations indicated by closed circles and closed triangles. (b) P-wave velocity structure used for hypocenter location in the study area, which is the same as that used for the hypocenter calculation in the ERI data processing system. Poisson’s ratio is assumed to be 0.25 in each layer.