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Crustal Structure in Northern Kwanto District by Explosion Seismic Observations

1958; Seismological Society of Japan; Volume: 11; Issue: 2 Linguagem: Inglês

10.4294/zisin1948.11.2_102

2186-599X

Research Group for Explosion Seismolgy,

Earthquake Detection and Analysis

At 01h 05m, Nov. 14, 1954 and at 01h 05m, Aug. 15, 1955, large amounts of explosives were fired near the Lake Nozori, Gumma Prefecture. At 01h 05m, Dec. 5, 1956, 1 ton of explosives was fired near Hokota town, Ibaragi Prefecture. 18 temporary observation stations for the Nozori explosions and 15 stations for the Hokota explosion were set up along the line connecting the Nozori and Hokota shot points. Each station was equipped with high-sensitive electro-magnetic seismometers with amplifiers. By these explosion-experiments the most probable crustal structure of nearly east-west section in the northern part of Kwanto District was deduced. It is shown in Fig. 7a. The depth of the Mohorovicic discontinuity was determined to be 25-30km. The depth of earthquake foci near Mt. Tukuba is generally found to be greater than 30km. Consequently earthquakes near Tukuba evidently occur in the upper part of the mantle.