Knowledge of the subsurface geometry of active faults, especially the geometry of seismogenic
faults, is key to understanding active tectonic processes and assessing the future's destructive
earthquakes. To reveal the relationship between surface active-faults and deep seismogenic faults, a
seismic reflection profiling system was introduced to the Earthquake Research Institute after the
Hyogo-ken Nanbu earthquake of 1995. Since 1996 seismic reflection profiling across active faults has
been carried out under cooperation with groups of Japanese universities and government research
institutions (Fig. 1). The active faults in Northern Honshu and Hokkaido have been focused as one of
the programs of multidisciplinary investigations on deformation processes of island arc crust. Seismic
reflection profiles were also acquired from active faults which show the higher slip rate, such as
Itoigawa-Shizuoka Tectonic line and Median Tectonic line active fault systems. Through seismic
reflection profiling, subsurface geometry of active faults has been revealed, such as a flat and ramp
structure in the upper most crust (Fig. 2) and active growth fold by blind thrust (Fig.3).