On the Velocity of Propagation of the Preliminary Tremors of the Great Kwanto Earthquake and the Area of the Seismic Origin

[摘要] From the durations of the preliminary tremors observed at various stations, the author, in his previous paper, located the seismic origin of the Great Kwanto Earthquake at a point to the north of Mt. Fuzi. In the present paper, he found the following two equations representing the relation between the distance of each station from the above point and the time of arrival of the first shock at that station in which Δ is the distance in kilometer and t the time in second measured from its origin assumed at 11h 58m, Sept. 1st, 1923. The first and second equations are well satisfied by the observed values of t and Δ at stations respectively in western and eastern Japan, the greatest discrepancy between the culculated and observed t being 2.7 seconds, while the total value of t ranges between 39-86 seconds. If the above equations are correct, there must be a time difference of 7 seconds for the commencements of the earthquake shocks at the seismic origin for the two waves, one travelling to the east and the other to the west. The author considers a highly strained state of earth crust, in a finite area near the origin, existing before the great earthquake and supposes that the waves actually started from the both sides of the area, whose diameter is about 50km, so that the apparent difference of time is accounted for.

[学科分类] 大气科学