断層の診断 (1) -山崎断層系-

The normal faulting outcrops are ordinarily observed at a region along the Sanda-Yamasakitectonic line, Southwest Japan. On the contrary, the results of the measurements of the crustalstress and studies of the mechanism of microearthquakes indicate that the horizontal and com-pressive stress acts in EW direction around this region. From these measurements and studies,it is expected that strike-slip faulting is observed at the outcrops. The normal faults observedat the outcrops are discordant with the stress which creates a strike-slip faults. This discordantis solved by the observation of a new outcrops in the Sanda region where the ground is preparedfor a housing. The sedimental layer was removed. On the new outcrops, we can observeda normal and reversal faults at the same time. The movement of a fault, concealedunder ground, brings about various kinds of breaks on the loose sedimental layer. Some ofbreaks are observed as a normal and reversal faults on the surface of the earth. Therefore,original type of fault has to be a reversal one, and a reversal fault has been worn away by erosionand streams. On the other hand, a normal fault holds its shape on the outcrop, because thehigher slope of a normal fault is stable. It is the reason why the observable outcrop is a normalfault in topography.