Crustal Structure in the Central Hokkaido, Japan, from a Seismic Refraction Experiment

The tectonic structure of Hokkaido is interpreted as forming by plate motions and associated secondary movements. Especially the Modern Kurile arc-trench system between Okhotsk and Pacific plates and also westward movement of Outer Kurile Arc has an important role on the tectonic evaluation in Hokkaido. To contribute to better understanding of this subject, a seismic refraction experiment was carried out by the Research Group of Explosion Seismology of Japan in Hokkaido in the autumn of 1992. The profile extends from Tsubetsu in the northwest of Hokkaido to Monbetsu in the southeast, running through the main tectonic belts: Sorachi-Yezo, Hidaka Mountains and Tokoro belts, from west to east. Four shots varying in size from 450 kg to 700 kg of explosives were detonated along the 180 km-long profile. The shots were recorded in mostly digital form at 184 recording sites. The results from this study indicate very complex structure under the Central Hokkaido. The upper part of the crust down to 20 km is resolved well by the refraction data