Abstract
At 01h 35m, 03h 35m on May 1, and again at 01h 35m, 03h 35m on May 3, 1954, four explosions were fired near Kamaisi Mine following the two former explosions of Dec. 7, 1952 and Sept. 13, 1953 in the same locality. The amount of charge of 01h 35m and 03h 35m explosion was 0.1 and 1.0ton respectively. 17 temporary observation stations were spread towards west and south for about 30km from Kamaisi City. Each station was equipped with high-sensitive electro-magnetic seismometers with amplifiers. These explosions were planned in order to ascertain the results obtained by the former five explosions about the crustal structure of the north-eastern part of Honsyû, i. e., the interface between the layers specified by the velocities 5.8km/sec and 6.1km/sec of P wave is shallower towards east and come across the earth surface near Kamaisi City. By the present explosion experiments these results were confirmed. It has become certain that there is an anticline of the layer with velocity 5.8km/sec of P wave, the axis of which is under the line connecting the shot points B and C and parallel to it. The final conclusion is graphically shown in Fig. 9.
