Geological indicators associated with paleoearthquakes: Focusing on the geomorphological evidences

In this study, I have categorized the evidences into two groups; geomorphological evidences (macroscale) related with surficial expressions and stratigraphic evidences (micro-scale) which is obtained from trench studies. This study is focusing on the geomorphological evidences to find the location of fault, to prove the existence of large earthquakes or not in the past from the geological point of view. Geomorphological evidences which are obtained from aerial photography and geological field excursion have been done for Tachikawa Fault, Itoigawa-Shizuoka Tectonic Line Active Fault System, and Sekiya Fault to test the reliability of geomorphological features indicating fault on the surface. Some of the evidences which are topographic altitude differences between both sides of the fault, displaced landforms, drainage patterns cut and displaced by main fault, geological unit differences, and lineament analysis have been investigated by using the aerial photographs for study areas. Other evidences which are used to check the reliability of data coming from aerial photography study, detailed geological unit description to find the deformation pattern produced by fault and to determine the exact location of fault, and preparation of geological map to define the boundary of units have been obtained by geological field excursion. For three study areas, firstly aerial photography study has been done to get the general idea about areas. Secondly, field excursion has been carried out to control the data from aerial photos and to obtain new evidences by using the geological evidences. Also, to examine the recent surficial expressions, Iwate-Miyagi Earthquake area is selected and geomorphological study has been carried out to discuss the critical situation for paleoseismology.