破砕帯の動きと直下の地震活動

阿武山での観測結果より

抄録

The movements of the fracture zone (strike N20°E, dip angle 20°W and thickness 1m) in the observational vault at Abuyama Seismological Observatory have been monitored by the two extensometers acrossing this zone. The movements of this zone are analyzed in this paper with special reference to the temporal variation of activity of small and microearthquakes occurring under the fracture zone.
The secular movement of this fracture zone is extension in approximately E-W direction with slightly left lateral component. Before the high seismic activity, however, it returns to contraction with slightly right lateral component. And after this temporal high seismicity, the fracture zone returns to extension.
The principal axis of compressional stress obtained by seismological and geodetical data lies constantly in E-W direction. The change of movement of the fracture zone may reflect the variation of stress in the high seismic layer (depth of 5-20km) under the fracture zone.