5-17 Imaging of active faults by seismic reflection profiling and long-term crustal deformation

 

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 central and Southwestern Japan 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 (Fig.2) 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 and active growth fold by blind thrust (Fig.3).

 

Fig.1. Location of shallow reflection seismic profiles acquired by cooperative projects.

Fig. 2. Seismic reflection profile across the Matsumoto-Bonchi-Toen fault, central Honshu, Japan.

Fig. 3. Seismic reflection profile across the Umaoi Hills, eastern edge of Ishikari Low Land, Hokkaido, Japan