To determine paleoseismic events from trench walls of active faults, precise observation of displaced horizon by fault are very important. However, fault traces in humic soil and peat are sometimes very difficult to detect. X-radiography was used to identify the fault plane in the samples from the Kamishiro trench across the Itoigawa-Shizuoka Tectonic Line.

The fault which is hardly identified on the eyes was succesfully identified by X-radiography. We described the detailed sampling method and condition of X-radiography. X-radiography is useful tool for the precise determination of paleoseismic event form trench walls.