The Fifth Explosion Seismic Observations carried out in the North-eastern Japan.

In the present experiment, effort of observation was concentrated in a region to the south of the blast point and with ⊿ within 300km. From P waves, a layer of 6.05km./sec. should overlie a lower layer of 7.2 or 7.6km./sec. with a corresponding thickness of 22 or 25km. This result is sufficiently supported by the observation of reflected waves. From S waves, a layer of 3.46km./sec. should overlie a layer of 4.5 or 4.8km./sec. with a corresponding thickness of 32 or 36km. As stated before, discrepancies in the results of the past several experiments arise probably from the inadequate assumption that the crustal structure is uniformly horizontal. The accumulation of data made so far may be sufficient for deduction of a more complicated structure which must be nearer the real state. This deduction should be made with all the available data by taking the geological and gravitational evidences into consideration.1953年9月13日に日鉄鉱業釜石鉱業所に於いて前回の1952年12月7日の大爆破に引続き第2回の爆破作業が実施せられた.爆破は前回同様落盤による災害発生防止のため脈石除去を目的とし,場所は前回の隣接地点で薬量は総計約42tonである.但し爆発は計画によれば20msづつおいて7段に分けてなされ,観測によると初段より終段まで84msを要した.爆破時刻は前回迄と同様な方法により,オッシログラムより3h04m57.074sと求められた