地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
地表近くで発生した極微小地震 (M=-3)
1984年長野県西部地震の余震
飯尾 能久
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ジャーナル フリー

1986 年 39 巻 4 号 p. 645-652

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We observed ultramicroearthquakes with a magnitude (J. M. A. scale) down to -3, by the highly sentitive aftershock observation of the Western Nagano Prefecture Earthquake of Sep. 14, 1984 (M=6.8).
The seismometer used is a 2Hz velocity-type transducer with flat response up to about 1kHz. Signals were recorded continuously on an analog data recorder. The overall frequency response of the observation system is flat from 2 to about 270Hz (-3dB point). Its highest sensitivity for the ground velocity was 18300V/(cm/s).
About 10, 000 earthquakes were recorded for the period of the observation. From them, the shocks of which S-P times <0.6s were chosen and analyzed. The total number of the earthquakes analyzed is 183. Their frequency-magnitude distribution and frequency-S-P time distribution were investigated. The earthquakes analyzed are distributed in magnitude down to -3. Their S-P times are distributed down to 0.05s.

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© 社団法人日本地震学会
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