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タイトル: 31. The Source Region of the Matsushiro-Swarm Earthquakes
その他のタイトル: 31.松代地震の震源過程
著者: Kasahara, Keichi
著者(別言語): 笠原, 慶一
発行日: 1970年9月30日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第48冊第4号, 1970.9.30, pp. 581-602
抄録: Teleseismic and near-field data of the Matsushiro earthquakes were studied collectively in order to clarify the source mechanisms of the swarm activity. The author first applied Aki's and Brune's techniques to the Love waves recorded at Gifu, 180 km southwest of Matsushiro, and found that the seismic moment of major swarm shocks is about 0.7~3.5×1022 dyne-cm for the magnitude range of 4.6~5.1. Stress drop for these shocks is then estimated at 0.6~7.0 bars, by assuming several other source parameters properly. Comparison of the retriangulation data with theoretical fault models proved that horizontal ground movements in the epicentral area are attributed fairly well to a buried strike-slip fault, as formerly suggested by geologists on the basis of surface evidence. Geometrical dimensions of the buried fault were thus estimated at 3km (deep)×7km (long), with surface cover of 0.5km (thick). Land offset across the fault plane for about 2 m was also estimated. As was discussed previously, the fault is believed to have grown rather gradually through the various stages of activity. From this point of view, possible contribution from nearby shocks to the fault development was studied on the basis of a simple dislocation model to explain observations fairly well. Analysis of leveling data resulted in another notable conclusion. The work done in the gravity field to achieve the observed land up heaval was estimated at approximately 1.7×1022erg, which is almost ten times as large as the total seismic energy released from there If this sort of energy originates from the strain energy in rocks, therefore, the apparent volume of seismic activity (30×15×5km3) seems too small to accumulate it. The crustal volume on a regional, scale should be assumed as the energy source for the present activity. Bulk increase of fractured rocks was pointed out as one of the possible mechanisms of the local land upheavals referring to the remarkable gravity change detected in the same area. Finally, research on the Matsushiro earthquakes by various groups was reviewed in order to develop a speculative picture of the seismic event which progressed in the Matsushiro area.|松代地震群の震源パラメーターをAkiやBruneの方法によって推定した.資料として岐阜におけるウィーヘルト地震計の記録を用いたが,それは皆神山麓に推定される潜在断層のほぼ真横の方位に同地が位置し,しかも非常にきれいなLove波が記録され解析に好都合であったからである.
URI: http://hdl.handle.net/2261/12529
ISSN: 00408972


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