5.上高地付近に発生した地震群について

概要

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On August 31 of 1969, a small earthquake activity occurred near Kamikochi, Nagano Prefecture and almost completely ceased toward the end of September. Magnitude of the largest shock was 5.0 by JMA. We analysed fifty-four earthquakes of this activity recorded at Hokushin Seismological Observatory and its satellite stations. Results of analysis are as follows. (1) Epicenters are located around the site 137°38:7E, 36°13:5N, 5km to the east of Mt. Yake. The dimension of the active region is about 5 km. (2) Daily frequency of the shocks did not show the feature of a swarm, but decayed following the formula, n=n1t-h, as in the case of typical aftershock sequences. (3) The value of "b" is 0.57±0.09, which is considerably less than that of earthquake swarms. (4) The direction of the compression axis is considered to be N125°E from the push-pull distribution of initial motions.
1970-03-31