A nested fault system with block rotation caused by left-lateral faulting: the Neodani and Atera faults, central Japan

Abstract

A detailed study of outcrops existing around the Neodani and Atera faults, which are large-scale, left-lateral faults oriented NW-SE in central Japan, revealed they were accompanied by two distinct fault systems of different scale and slip sense; intermediate-scale, parallel, right-lateral faults and small-scale, parallel, left-lateral, kink bands or faults. A nested fault model with different geometric scales is proposed to explain the hierarchical occurrence of the fault systems. In this model, the secondary fault system is contained within the primary fault system as a mirror image of it. Left-lateral movement of the Atera or Neodani fault induces right-lateral movement of intermediate-scale faults and results in counterclockwise rotation of the blocks between the faults. This right-lateral movement in turn induces left-lateral movement of small-scale faults or kink bands, which causes clockwise rotation of the small blocks between them. Since the angle of the counterclockwise rotation of the primary fault systems is the same as that of the clockwise rotation of the secondary fault system, these rotations cancel each other. While the large-scale fault movements cause block rotation, the small blocks eventually show no rotation.