Large crustal deformations have occurred in the Northeast Japan arc due to the earthquake off the Pacific coast of Tohoku (Mw 9.0) on March 11, 2011. Along with this massive earthquake occurred in the Japan Trench, the condition for failure on the Northeast Japan arc and surrounding active faults across Japan has changed. Identifying the detail deformation pattern is the key to minimizing the danger they pose. To date, the deformation pattern investigation in the Futaba fault zone is considered to be limited. Previous studies that delineated the fault trace was constructed based on interpretation from aerial topography and small scale topographic map which has significant limitation and uncertainty due to dense vegetation. This study examined the Haramachi segment focusing on the area where it is lacking of detail investigation and to validate the timing of the most recent faulting event more broadly.
Geomorphic features associated with active fault deformation of the Haramachi segment have been examined by utilizing high resolution DEM and several types of topographic anaglyph images. Subtle surface expression of deformation associated with faulting such as deformed terrace surface, deflected drainages, deformed ridge, and linear valley can be identified. Several new fault strands are identified in this study, which is supported by fault outcrops found in the field that confirms the evidence of displacement. The most prominent fault scarp was observed near Uda River and Shiode Mountain area. The fault displaced the lowest fluvial terrace surface indicating most recent surface rupturing event. In attempt to validate the timing of the deformation, borehole survey on this terrace tread was conducted to collect the material suitable for radiocarbon dating. The soil organic material was analyzed using AMS method is yielding 3694 y.BP, which indicated the maximum elapsed time since the most recent surface rupturing event on the Haramachi segment.
Keywords: Tectonic Geomorphology, Haramachi Segment, Futaba Fault Zone, Northeast Japan
