Determination of Seismic Origin by means of Omori's formula

[摘要] In this paper, the seismic origin means an underground point where the seismic disturbance sets in earliest. The formula given by Prof. F. Omori showing the relation between the distance of this point from the place of observation and the duration T of the preliminary tremor, is Δ=7.42T, where Δ is measured in km. and T in sec., which is applicable for 0<Δ<1000km. The author applied this formula to find the seismic origin of the Great Kwantô Earthquake of Sept. 1. 1923, referring to the seven seismograms taken at the meteorological observatories at Kôhu, Numadu, Tôkyô, Kumagae, Maebasi, Matumoto and Kôbe, and also to another obtained at the Geophysical Observatory of the University, Sendai. Eight spheres with radii of the calculated Δ's for, and centers at the respective plac_??_s of observation meet together nearly at a point as shown in the figure shown in p. 115, with a depth of 40 km. Thence the author concludes that the seismic origin was situated at a point a little north of Mount Fuzi, and also that the formula of Prof. Omori is exact. (S. F.)

[学科分类] 大气科学