Tectonic Context of the Study Area

Abstract

The tectonic setting of the study area, the Osaka sedimentary basin, is described from the viewpoint of changes in the plate motion around the northwestern Pacific that have occurred over the last one hundred million years and a sequence of epoch-making migration and deformation events along the southwestern Japan arc that has been investigated based on paleomagnetism and seismic interpretation. The ongoing active but subtle deformation of the island arc is also evaluated using high-resolution remote sensing data. The considerable diversity in geomorphological features and the uneven development of active faults point to the existence of a buffer zone of strong crustal strain in southwest Japan (i.e., the Kinki Triangle), where the Osaka basin is located. The dimensions of the sedimentary basin were assessed based on the gradient tensor analysis of gravity anomaly data, which revealed a deep-rooted basin morphology controlled by the architecture of major faults. To unravel the paradox of the Osaka basin having developed at a confining bend or the step of an arc-bisecting transcurrent fault, numerical modeling was used to replicate the pattern of uplift and subsidence. Such a simulation is useful for the detection of tectonically significant faults in the basin-forming process.