微小地震観測網から求めた和歌山地方の地震の発震機構 (第2報)

抄録

On the bases of the fault plane solutions that have been obtained in the first paper, a statistical study has been made on the state of stresses that generated those earthquakes and the types of faultings both for the shallower earthquakes (H<20km) and the deeper earthquakes (H≥20km) in Wakayama region.
The average direction of P axes (the maximum pressure axes) for the shallower earthquakes was oriented horizontally along N 122.9°E direction. It has been inferred that the shallower earthquakes in Wakayama-Arida region showed components of thrust faultings and the stress state in this region might be σ₁>σ₂≈σ₃ and that the shallower earthquakes in Hidaka region were characterized by strike slip faultings.
Because number of the fault plane solutions of the deeper earthquakes was 23, we could not discuss in detail the stress state in the upper mantle of this region. But the solutions of 23 earthquakes have suggested that the T axes (the maximum tesion axes) might change their orientations from E-W to NE-SW according to the shift of their location from the Kii channel to the central part of the Kii peninsula and that the P axes might be in the N-S direction in the Kii channel and be in the same direction as that of the P axes of the shallower earthquakes in the central part of the Kii peninsula.