Revealing the distribution of active submarine faults off the coast of Oga Peninsula using high-resolution stereoscopic topographic images

Abstract

This study aims to elucidate the importance of a combination of tectonic geomorphological interpretations using high-resolution stereoscopic topographic images and seismic profile interpretations as methodological standards for organizing maps of the distribution of active submarine faults. Furthermore, we provide topographic evidence of active submarine reverse faults off the coast of the Oga Peninsula, which lies on the eastern margin of the Japan Sea. First, the study reprocessed the point cloud data of multi-beam bathymetry data and produced a new digital bathymetry model and anaglyph images. These images and contour maps enabled the identification of broad deformation and other small-scale tectonic landforms, such as fault scarp, fault scarp on the flat surface of a basin, and flexure scarp. We first described detailed tectonic landforms along the NE–SW trending northwest-dipping faults across the Mogami Trough, which was identified by previous geological studies, to demonstrate the effectiveness of the proposed method. Moreover, we applied the method as an applicable example for tectonic landforms in the east-dipping fault at the offshore of the Oga Peninsula with seismic profile interpretation. The result demonstrated that an active fault across the central part of the Mogami Trough can be recognized on the bases of geology and topography. However, identifying an active fault that extends to the area with poor sediment deposition at the northern end of the trough is difficult. The study found that detecting active fault distribution by tectonic geomorphological interpretation is practical and effective using a stereoscopic image from high-resolution topographical data. Moreover, a new east-dipping reverse fault, that is, the Kyurokujima-nansei-oki fault, was discovered along the eastern margin of the northwestern part of the Mogami Trough by identifying flexure scarp and comparison with seismic profiles. The strike of the Kyurokujima-nansei-oki fault is parallel to that of the aftershock distribution of the southwest part of the 1983 Central Japan Sea Earthquake and resembles an east-dipping structure. Thus, this fault should be considered one of the source faults during assessments of seismic and tsunami hazards.