1969年9月9日岐阜県中部地震の余震活動
1971 年 24 巻 2 号 p. 117-128
詳細
1971 年 24 巻 2 号 p. 117-128
An aftershock sequence accompanied by the earthquake occurred at the central part of Gifu Prefecture on Sept. 9, 1969 was studied. Because of short epicentral distances, a number of shocks were recorded at the Inuyama seismological network from the beginning of the main shock to the end of the November of 1970. These data were useful for the long-term investigation of the aftershock sequence. Those data recorded at Takayama seismological station and temporary stations at Hirayu and Okuzumi were also used in this study. The following results were obtained:
1) Epicenters of aftershocks were distributed along NW-SE direction. It was likely that they were represented by a two dimensional normal distribution with standard deviations of 2.2-3.5km and 3.5-5.0km across and along an assumed fault, respectively. The epicentral region was found to spread gradually towards both sides of the fault.
2) With the use of both data recorded at Inuyama and J. M. A. networks, the epicenter of the main shock was recalculated to the point where aftershocks were clustered.
3) The daily frequency of aftershocks for 450 days from two hours later from the main shock was well represented by single formula, n(t)=k·t-p, with p=0.95.
