Post-earthquake airborne LiDAR DEM and field investigation reveal the details of the northernmost trace of previously reported surface rupture zone associated with the 2008 Iwate-Miyagi Nairiku earthquake, which displaced the southern slopes of the densely forested Mt. Kunimi, Oshu City, Iwate Prefecture. The LiDAR DEM allows us to unveil the distribution and slip sense of the fresh ruptures that occurred on the mountainous area. Field observation and in-situ digital surveying show that the rupture is characterized by i) curvilinear traces composed of the N-S-trending east-facing scarp with no lateral offset to the south and the NW-SE-trending northeast-facing scarp with sinistral offset to the north, ii) the uphill-facing flexure scarps that move up the southwestward-sloping mountain block toward the upslope direction with ＜1.0 m vertical offsets, iii) shortening deformation manifested by intrusion of trees on downthrown side into the upthrown side, and iv) continuous trace extending over 2 km in length. These features suggest that the rupture is a west dipping reverse fault accommodating W-E to WNW-ESE trending compression, which is consistent with several proposed source fault models inferred from seismological and geodetical studies. The location of the surface rupture corresponds to the zone of abrupt change in displacement gradient illuminated by SAR analyses. Furthermore, the large slippage at the northernmost part of the 2008 rupture zone well corresponds to the location of one of large slip patches on the causative fault as derived from waveform inversion. Together with the detail topographic measurements and trench excavations, we identified evidence for the past faulting behavior suggestive of the same slip sense along the rupture zone. We thus conclude that this portion of the surface rupture is tectonic origin reflecting the westdipping seismogenic reverse faulting.
