[SCG57-P07] Seismic reflection profiling across the Median Tectonic Line (MTL) active fault system in Ehime and Tokushima Prefectures
Three seismic lines were deployed perpendicular to the MTL and major geologic boundaries. The length of seismic lines is 11 km (Saijo area, Ehime), 4.8 km (Wakimachi area, Tokushima) and 6.4 km (Awa area, Tokushima). To obtain a high-resolution seismic image of the shallow part of MTL, a 10-m spacing receiver array was formed using offline recorders. The seismic source was vibroseis trucks. The sweep signals (5-100 Hz for high resolution reflection profiling, 5-40 Hz for refraction profiling) were recorded 10 Hz vertical geophones. The seismic data were processed using conventional CMP-reflection methods.
The high-energy shot gathers at Saijo seismic line clearly demonstrate the reflectors at 1.5, 2-3, 4 sec. (Two-way travel time). The reflectors from 2-3 s (TWT) are interpreted as northward dipping Sambagawa Metamorphic belt. The seismic sections portray the seismic image down to 2 km in Wakimachi and Awa area. The reflectors are interpreted as northward dipping Sambagawa Metamorphic belt. These structural characters found in the seismic section may show that the deeper extension of MTL shows northward dipping in Shikoku.