Reactivation of an old plate interface as a strike-slip fault in a slip-partitioned system: Median Tectonic Line, SW Japan

Evolution of the Sea of Japan back-arc and some unsolved issues

“…One of these faults which runs through SW Japan, the MTL, is an important data point in any reconstruction ( Figure 2). Recently, it has been re-interpreted as an ancient subduction megathrust based on new seismic imaging that shows a 40°dip Sato et al, 2015a). If we accept a megathrust origin for the moderately-dipping MTL, then it would have been a major structural feature along the pre-rift continental margin, and not necessarily a natural extension of other regional strike-slip faults, particularly those more nearly vertical.…”

Cambrian plutonism in Northeast Japan and its significance for the earliest arc-trench system of proto-Japan: New U–Pb zircon ages of the oldest granitoids in the Kitakami and Ou Mountains

“…For example, the MTL in SW Japan was re-evaluated as a strike-slip fault activated not during the Cretaceous as previously believed, but merely in the Quaternary (Isozaki, 1996;Sato et al, 2015). A recent seismic profile clearly illustrated the north-dipping sub-horizontal structure of the MTL that transected and dissected the entire arc crust of SW Japan (Ito et al, 2009), and this post-late Cretaceous structure is inconsistent with the claimed Cretaceous oblique subduction and resultant large-scale dislocation.…”

“…A recent seismic profile clearly illustrated the north-dipping sub-horizontal structure of the MTL that transected and dissected the entire arc crust of SW Japan (Ito et al, 2009), and this post-late Cretaceous structure is inconsistent with the claimed Cretaceous oblique subduction and resultant large-scale dislocation. The MTL is better explicable as a low-angle thrust that was activated during the Miocene back-arc (Japan Sea) opening associated with across-arc contraction in the fore-arc (Isozaki, 1996;Isozaki et al, 2010;Aoki et al, 2011;Sato et al, 2015). Under the circumstances, we need another feasible and more viable explanation for the disappearance of the old arc granitic belt.…”

Three-Dimensional Architecture of the Median Tectonic Line in Southwest Japan Based on Detailed Reflection Seismic and Drilling Surveys

“…Before the national project, detailed geologic surveys including the excavation of surface ruptures [6] have been used to describe the superficial deformation pattern along the fault, and a series of offshore [7] and onshore [8] seismic studies have been presented as useful profiles across the fault. As for the western half of the peninsula, a tectonic model has been proposed to strike a balance between the fault structure and its dominant motion senses [9]. However, the threedimensional architecture of the MTL, one of the largest intraplate faults in the world, has never been addressed by means of detailed seismic data with a reliable stratigraphic control on deep boreholes; this theme was the focus of the present study.…”