The Itoigawa-Shizuoka tectonic line (ISTL), which is located between the NE and SW Japan arcs, is one of the most major tectonic lines in Japan. The N-S trending Kamishiro fault located in the northern part of the ISTL active fault system is an east dipping reverse fault. Near the southern part of the fault, the alluvial fan formed by a river flowing toward the southeast is tilted to the west by faulting. To reveal shallow subsurface deformation structure above a depth of 5 m, we carried out ground penetrating radar (GPR) profiling along two survey lines, whose lengths are 50 m and 130 m, respectively, across the fault. The GPR data was collected by common-offset modes using the control unit SIR-3000 (Geophysical Survey System Inc.) and the 200 MHz antenna Model-5106(Geophysical Survey System Inc.), and the station spacing was 0.01 m. The depth converted GPR sections after careful data processing are very concordant with the geological section based on drilling and trenching surveys conducted near the GPR survey. The GPR sections show deformation structure of the fan deposits in detail. The vertical displacement of the top of the fan gravel deformed by the Kamishiro fault is over 3.0 m during the last faulting event.
