We excavated a trench across the Kawakami fault, one of the segments of the Median Tectonic Line Fault Zone in southwest Japan. Three faults appeared on the trench walls. The sense of apparent displacement across the fault zone is down to the north, consistent with the fault scarps around the trench site. The sediments exposed on the trench walls contain evidence for three episodes of surface-rupturing earthquakes. The most recent seismic event, event I, on the Kawakami fault occurred after AD 1405. The penultimate seismic event, event II, occurred sometime during 790 BC-AD 65. Another seismic event, event III, occurred sometime during c.a. 29,000 yBP-560 BC. The timing of these seismic events is consistent with that revealed by previous trenching studies. The ages of the most recent and penultimate events are better constrained in this study. By combining this study with previous study results, the timing of paleoseismic events on the Kawakami fault is summarized as follows. The most recent seismic event, event 1, occurred between AD 1405 and AD 1780. The timing of the event is consistent with the 1596 Keicho-earthquake. The penultimate seismic event, event 2, occurred during AD 25-AD 1000. Other events occurred during 790 BC-AD 65 and during c.a. 29,000 yBP. -560 BC. Given that the 1596 Keicho-earthquake is the latest faulting event of the Kawakami fault, the average recurrence intervals are inferred to be 765-1193 years.
The 1957 M8.3 Gobi-Altay, Mongolia, earthquake was caused by the rupture of the eastern part of the Gobi-Altay active fault zone and produced 260-km-long surface ruptures with maximum horizontal and vertical displacement of 7 m and 5 m, respectively. We mapped these rupture traces based on geomorphic stereo analysis of CORONA satellite imagery and compared our map with the previously-reported detailed distribution map of the ruptures. We identified active fault traces that moved during the 1957 earthquake based on displacement of modern river beds or very young fluvial surfaces adjacent to them. We conclude that 1) we are able to identify the 1957 surface ruptures using CORONA imagery, 2) we are able to clearly interpret branch directions along surface ruptures. However, we are occasionally not able to detect the surface ruptures because of a) small vertical displacement of less than 1 m that is less than the threshold to identify any surface ruptures using CORONA imagery, b) distortion that impedes stereo analysis itself as well as scale reduction in the edge portion of CORONA imagery, and c) weak geomorphic expression due to small amounts of both coseismic and cumulative displacement. This study demonstrate that geomorphic stereo analysis using CORONA satellite imagery enables us to reconstruct details of recent surface ruptures that appeared several-ten years before the imagery was taken during AD 1959 and 1972, or perhaps several-hundred years before that period in arid areas where external geomorphic processes do not work so frequently.
We photographed for the geomorphometry of the Midori fault scarp formed by the 1891 Nobi Earthquake in Motosu City, Gifu Prefecture (Japan) by using multirotor radio control helicopters as a small unmanned aerial vehicle (sUAV), and we analysed these images. A digital surface model (DSM) of 0.09 m mesh and an orthophoto with a resolution of 0.03 m were generated from these images by PhotoScan software produced by structure from motion (SfM). A topographic map with 1 m interval contours and a cross-section profile were processed using a DSM produced by ArcGIS. These results were compared with the same type of map and profile processed by LiDAR with a resolution of 5 m. The terrain was able to be measured by using the DSM derived by SfM with precision at least as high as that of the LiDAR. We expect that the new technology will be applied to tectonic landform survey and geomorphological research. In addition, our results should help to ensure flight safety and compliance with the law.
The Atera fault zone is a left-lateral active fault zone in central Japan which is about 70 km in length and strikes NW-SE and NNW-SSE. The Kashimo area which is located in the central part of the Atera fault zone indicates the most complicated fault geometries. In this area at least two active faults, the Atera and the Owachi faults, are aligned parallel in a narrow range. In order to understand the developmental process of this fault zone, it is important to clarify the activities and the histories of each active fault in this zone. In this study, we have identified some faulting events in a newly found outcrop at Nagahora site in Kashimo area. The occurrence of the undoubted faulting event was about 3,500-4,800 years ago (Event 3). The occurrences of uncertain faulting events were about 2,800-4,800 years ago (Event 2), and after about 3,200 years ago (Event 1), although the possibilities that these two events had occurred at the same time with Event 3 have remained. It was considered that the faulting events have repeated at least 50,000 years at this site, because the occurrence of another event was identified during the deposition of sediment of M2 terraces.