[S08-P] Poster

[S08-P-01] Description and interpretation of the surface ruptures in northwest of the outer rim of the Aso caldera triggered by Kumamoto Earthquake

^○Hiroshi Une¹, Takayuki Nakano¹, Satoshi Fujiwara¹, Tomokazu Kobayashi¹, Yu Morishita¹, Kazumi Iwata¹, Hiroshi, P. Sato², Hiroshi Yagi³ (1.Geospatial Information Authority of Japan, Tsukuba, Japan, 2.Nihon University, Tokyo, Japan, 3.Yamagata University, Yamagata, Japan)

Associated with the 2016 Kumamoto Earthquake, many surface ruptures were emerged in northwest area of the outer rim of the Aso caldera, which were located apart from the Futagawa and Hinagu Fault System, considered as the source fault of the earthquake,　and rarely accompanied by seismicity. Overall distribution and deformation patterns of the surface ruptures in this area were shown by satellite radar interferometry analysis using ALOS-2 data, suggesting half-graben-like normal faulting triggered by north-south tensional stress field derived secondarily from the stress changes associated with the main source faulting (Fujiwara et. al. 2016, Morishita et. al. 2016). We carried out field surveys and identified characteristic surface ruptures at many places. Some of those have characteristics in shape that can be misread as surface earthquake faults. Recently such passive, or “accompanied" deformation of existing structure triggered by the change of stress field or seismic motion associated with earthquakes have been often reported since SAR interferometry has enabled the seamless and detailed understanding of surface deformation. These passive deformation might have occurred not specially for the reported events but universally in nature. Such passive deformation may be possibly included in the list of past surface earthquake faults and events recognized by trench surveys. We should start the discussion on the issue of reexamination of identification of characteristic earthquake events of active faults.