Four earthquakes of M=2.8, 2.9, 4.0, and 4.1 occurred at the north part of Osaka Pref. in Japan, which were accompanied by many aftershocks. The great part of energy of each aftershock sequence was released within a day after the respective main shocks. The focal mechanism of the aftershocks was similar to that of the respective main shocks, but different types were also found.
The “b” was examined on each aftershock sequence, and 0.53, 0.87 and 0.70 were obtained. It is supposed that those values are related to the focal depth.