Abstract
Explosion seismic experiments were carried out in 1980 for the investigation of the crustal structure in the northeastern part of Shikoku. Sixty-three seismograms were obtained at 42 temporary stations aligned on the two N-S trending parallel profiles crossing the Median Tectonic Line which is the most prominent geotectonic line and the greatest active fault in Japan. A P-wave velocity structure of the surface and granitic layers was obtained from the first arrival time data. A structure of the deeper part of the crust was also roughly estimated from the later arrivals. The Median Tectonic Line was estimated to be a north-depressed fault with a vertical offset of up to 2km in the shallow velocity profile. A possibility of the extension of the offset further downward to the deeper crust is also suggested.
