The Northern Miyagi Earthquake, which was slightly destructive around the epicentral region, occurred in the northern part of the Miyagi Prefecture, Northeastern Japan, at 02h26 m GMT, April 30th, 1962. The magnitude of the earthquake was estimated at 6.4 by the Sendai District Meteorological Observatory, Japan Meteorological Agency, and at 6.2 by the Earthquake Research Institute. Aftershocks of this earthquake were investigated on the basis of the observational data at the seismological station at Mt. Tsukuba of the Earthquake Research Institute, about 300 km distant from the epicentre. Daily numbers of earthquakes observed with the ""HES 1-1"" seismograph (Vmax≒30,000, T1 = 1.0 sec, T2 = 1.0sec) and ""HES 1-0.2"" seismsgraph (Vmax≒150,000, T1 = 1.0 sec, T2 = 0.2sec) are shown in Figs. 3 and 4, respectively. Hourly numbers and three-hourly numbers of them are shown in Figs. 4 and 5, respectively. They indicate that these seismographs recorded several hundred aftershocks of the Northern Miyagi Earthquake in a few days after the main shock. The earthquakes which were recognized as the aftershocks on the basis of the p-s time and the configuration on the ""HES 1-1"" seismograms were selected in Table 2. The magnitudes of larger aftershocks were determined directly from the Anderson-Wood seismograms. For determining the magnitude of smaller shocks which were not recorded on the Anderson-Wood seismograms, we extended the proportional relation between the two maximum trace amplitudes on the Anderson-Wood seismogram and on the "" HES 1-1"" seismogram for larger shocks. The magnitude of the main shock was estimated at slightly larger than 6.2. The two larger aftershocks had magnitudes of 5 and four had magnitudes larger than 4.5. The magnitude frequency distribution of the aftershocks is shown in Table 3. The "" HES 1-1"" seismograph was able to obtain full seismogroms of the aftershocks larger than M=3.0 and the ""HES 1-0.2"" recorded the aftershocks smaller than M=3.0 at the epicentral distance of about 300 km.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
40
号
3
ページ
625 - 637
発行年
1962-11-30
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
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筑波山で観測された1962年4月30日宮城県北部地震の余震
ji0403014.pdf
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