Observation of High Frequency Seismic Waves by a Hydrophone just above the Focal Region of the 1980 Izu-Hanto-Toho-Oki Earthquake and a Precise Estimate of Location of the Submarine Earthquake Fault
An observation of high frequency seismic waves by a hydrophone was carried out just before and after the Izu-hanto-toho-oki earthquake of M 6.7 on June 29, 1980 and just above the focal region of this submarine large earthquake in cooperation with the Hydrographic Department, Marine Safety Agency. About one thousand high frequency (50-300 Hz) seismic events, which are called acoustic emission in this paper, were observed after the large earthquake. There are various types of acoustic emissions of different wave-forms and they are classified into the three types A, B and C. In type A, the amplitude increases very abruptly and then decreases gradually. This type might occur in the very shallow region of the earth's crust just below the observation ship. Types B and C in which the amplitude increases more gradually might occur at more distant or deeper regions. When the ship passed through a limited region, acoustic emission events of A type were observed very frequently. Therefore, it is deduced that the earthquake fault of M 6.7 passed through this limited region, 8.5km±0.5km distant from the east coast of the Izu peninsula. On the other hand, the source mechanism analysis shows that the earthquake fault is a left lateral vertical strike-slip fault with the NS direction. Thus, it is concluded that the earthquake fault in the NS direction is located about 8.5 km from the east coast of the Izu peninsula and the fault plane reaches to the ocean botton surface. This locality of fault is significantly different from that of a geologically estimated active fault in this region. This precise estimation of location of the submarine earthquake fault by acoustic emission measurement shows a new method very different from the conventional seismic method. It is thought that the high frequency seismic observation may be useful also for earthquake prediction.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
55
号
4
ページ
1017 - 1041
発行年
1981-03-31
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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1980年伊豆半島東方沖地震の震源直上でのハイドロホンによる高周波振動の観測とそれによる地震断層の位置の推定
ji0554006.pdf
(1.48MB)
