糸魚川-静岡構造線活断層系神城断層の浅層および極浅層反射法地震探査

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The Kamishiro fault forms the northern-most part of the Itoigawa-Shizuoka Tectonic Line (ISTL) active fault system. This fault displaced young lake deposits in the Kamishiro basin, and the shallow (less than 20m) structure of the fault and an average long-term vertical slip rate of 2.2－2.7m/kyr were revealed by drilling and geomorphological investigations. To reveal the subsurface structure of this fault system and estimate long-term net slip rate, we carried out S- and P-wave high-resolution shallow seismic reflection profiling across the Kamishiro fault. The S-wave seismic line is 200m, the receiver point intervals are 1m, and the shot point intervals are 2m. We used a 192-channel seismic system with a mini-vibrator to image the depth range of 5 to 70m. The P-wave seismic line is 2.1km, the receiver point intervals are 10m, and the shot point intervals are 10m. We used a 176-channel seismic system with a mini-vibrator to image the depth range of 50 to 800m. From these experiments, it is clarified that the Kamishiro fault cut and fold the lacustrine deposit. The deformation is associated with fault development near the surface. Given the dip angle of the Kamishiro fault determined by S-wave seismic profiling to be approximately 30°, the average dip slip-rate is calculated to be 4.4-5.4m/kyr. And, the Kamishiro fault corresponds to cutting across the anticline rather than the deformation front on the P-wave seismic profile. The fold is related to blind thrust fault, fold propagation fold, or drag structure.
東京大学の論文
2007-08-20

糸魚川-静岡構造線活断層系神城断層の浅層および極浅層反射法地震探査

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