Backarc deformation along the eastern Japan Sea margin, offshore northern Honshu

Abstract

The structural evolution of the eastern Japan Sea margin offshore northern Honshu, is discussed on the basis of single-channel seismic profiles. Backarc structures evolved in response to late Oligocene–Middle Miocene extension, which was generated at high angles to the arc/trench system. The evolution of a Late Miocene–Recent compressional plate-tectonic regime resulted in widespread basement inversion. The eastern Japan Sea margin is characterized by variable inverted half graben systems, which are obliquely oriented to the island arc. The area is underlain by three major structural blocks, which are separated by a NW- and a WNW-trending structural discontinuity. These blocks experienced a northward increase in extension. The two southern blocks contain NNE–NE oriented reverse faults, while the northern block is underlain by N–NNW trending reverse faults. The orientation and geometry of basement faults compares well with faults mapped onshore Honshu. The evaluation of the eastern Japan Sea margin can be explained by Early Miocene ESE-directed extension followed by a Middle Miocene SSE-directed extension. Pliocene–Recent east-dipping reverse faults extend along the base of the continental slope and form a discontinuous thrust front, which is characterized by minor fault offsets. These reverse faults are locally associated with small active arc volcanoes.