Yasuhiro Suzuki

Surface ruptures associated with the 2014 Kamishiro fault earthquake (Mj 6.7), appeared along the Itoigawa-Shizuoka Tectonic line active fault system in the northern part of Nagano Prefecture, central Japan. We photographed it with digital cameras mounted on an unmanned aerial vehicle (UAV). Digital surface models (DSMs) were generated from the acquired photographs by applying SfM-MVS technology. The UAVs used in this study were the F450 and Phantom 2 manufactured by DJI Inc., and the cameras were the GR model manufactured by RICOH Inc. and were attached to each UAV for aerial photography. The ground control points required for generating DSMs using SfM-MVS analysis were measured using an RTK-GNSS (Leica GPS900), and the topographic profiles used for the accuracy assessment of the DSMs were measured in situ using a total station (Leica TCR705) and digital auto level (SOKKIA SDL50).<BR>As a result, we were able to create DSMs and ortho-photographs at the resolution of a few centimeters. The accuracy was assessed by comparing the topographic profiles measured by the total station and leveling with those generated by the DSMs. Validation against the nine topographic profiles revealed that the DSM had a relative height error of 4.0cm with an average standard deviation.<BR>Taking photographs from a UAV is one of the quickest and most cost-effective methods to record detailed surface topography. Generating a DSM of surface ruptures using UAV photography with SfM-MVS is particularly advantageous because ruptures will change their features quickly, and surface topographic variations of 10 cm or less cannot be recognized in field observations.

<p>The 2014 M 6.7 Naganoken-hokubu earthquake was caused by movement of the Kamishiro fault located in the northernmost part of the Itoigawa-Shizuoka Tectonic Line (ISTL) active fault system, central Japan. We conducted a series of field research immediately after the earthquake to describe coseismic surface ruptures. Our description methods were: 1) field reconnaissance using pre- and post-earthquake airphotos; 2) quick measurement using staff; 3) topographic profiling using Auto Level and Total Station; and, 4) UAV and highpole SfM measurement. We identified 9-km-long coseismic surface rupture, most of which was located along the pre-existing surface trace of the Kamishiro fault. The maximum value of coseismic vertical offset was ca. 1 m or more, which was recorded at Oide in the northern part of the rupture. Based on comparison of the 2014 coseismic slip distribution with the long-term slip rate distribution, both 2014 slip amount and cumulative offset amounts of L2 and L3 terrace surfaces are larger in the northern end of the ruptures. This implies that the subsurface coseismic slip during pre-2014 earthquakes continued toward the north, similar to that during the 2014 earthquake. In addition, both coseismic slip and long-term slip rate becomes smaller toward the south, indicating that the Kamishiro area is one of the segment boundaries in the northern part of the ISTL active fault system. Further investigations of the 2014 earthquake and the Kamishiro fault are needed to understand formation of tectonic landforms, landscape development, or earthquake prediction model of active faults.</p>