郷土資料と陸地測量部による正式2万分の1地形図に基づく布田川断層帯北甘木断層の位置の再検討と2016年熊本地震に伴い出現した地震断層

抄録

　 Precise location and distribution of active faults provide essential information for predicting damage caused by fault displacement. However, in regions where human activity continues for a long time, faulted landforms indicative of the fault trace might have been destroyed or modified by past land improvement, which makes precise mapping of the active faults difficult. Examinations of local documents concerning the intense cultivated land consolidation works carried out in the late 1920s and old 1: 20,000 topographic maps issued by Japanese Imperial Land Survey in the 1900s allow us to revise the location of the Kita-amagi fault, a structural element of the Uto section of the Futagawa fault zone in central Kyushu, which has been mapped primarily based on interpretation of aerial photographs taken in the 1940s or later. Validity of the revision is verified by appearance of the surface ruptures on the Kita-amagi fault formed in association with the 2016 Kumamoto earthquake sequence, although the surficial slips are small and scattering. To assess whether the tectonic landforms along the Kita-amagi fault have been created by repetition of small and faint surficial slips as observed during the 2016 event or repetition (or combination) of other events that has been accompanied by more large and continuous surface deformation, further comprehensive investigations including paleoseismic trenching should be needed.