抄録
Subsurface fluid migration through cracks is controled by the state of stress. It is widely believed that reverse-faulting regime of stress prevails in folding. However, our recent field observations revealed that there are unexpectedly many strike-slip faults in the central part of the Niigata fold belt. A latest stress inversion technique showed that the sigma-3 axis was horizontal and parallel to fold axis at least the observed shallow levels of the crust in the area.
This paper firstly reviews the methodological development of stress inversion for the last 30 years. Secondly, the application of the multiple inverse method, one of the latest inverse methods, to the Niigata fold belt is introduced. It is suggested that vertical fluid migration was more rapid than expected in the area due to the opening of pre-existing vertical fractures by the horizontal sigma-3 axis.
