Relation between the crustal structure type and the distribution of the crustal deformation in the Japan Sea back-arc basins and its margins

Abstract:

The Japan Sea located in the northwestern Pacific has three major back-arc basins. Based on previous results, it is suggested that the back-arc opening of the Japan Sea was taken from the Early Oligocene to the Middle Miocene (e.g., Tamaki et al., 1992). From 3.5 Ma, in the eastern and southwestern margins, the crustal shortening by a strong compression occurred (Tamaki, 1988; Sato, 1994). Because of this opening and this shortening, the deformation such as active faults and folds has developed in these margins (e.g., Okamura et al., 2007). The Japan Sea has a unique tectonic setting to clarify the relationship between the back-arc opening process and the crustal deformation. However, we have little information concerning with a crustal structure formed by the back-arc opening and distribution of the crustal deformation. To obtain this information, we have been carrying out active-source seismic surveys using ocean bottom seismographs (OBSs) and multi-channel streamer system (MCS) to cover these margins of the Japan Sea.

The margin of the southern part of the Japan Sea has two crustal types. One is a thicker oceanic crust in the basin area (Yamato Basin), and the other is the rifted continental crust in the continental shelf in comparison with crustal structures of typical oceanic type (White et al., 1992) and of the northeastern Japan Island arc (Iwasaki et al., 2001). On the other hand, in the margin of the northern part of this Sea, the crust is divided into three types; the oceanic crust in the basin area (Japan Basin), the thicker oceanic crust in the transition area from the basin to the continental shelf, and the rifted continental crust in the continental shelf (No et al., 2014). In the distribution of the crustal deformation, the southern part differs from the northern one, like the crustal structure type. These might show that the distribution of the crustal deformation is related to the crustal structure types.