巻号一覧
前身誌
61 巻, 1 号
選択された号の論文の3件中1～3を表示しています
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論説
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—本震発生以前の平成 16年（2004年）新潟県中越地震の震源域および山形盆地断層帯南部の例—古澤 豊, 長谷見 晶子, 吉本 和生2008 年 61 巻 1 号 p. 1-10
発行日: 2008/08/31
公開日: 2013/09/10
ジャーナル フリーWe relocated hypocenters around active faults to investigate the relation between the hypocenter distribution and the subsurface geometry of the faults. We selected two regions. One is the source region of the 2004 Mid-Niigata Prefecture Earthquake. 179 earthquakes which occurred in the source region during about 2.5 years before the main shock were relocated by applying the double-difference earthquake location algorithms (the DD method). The hypocenters gathered in a narrow area after relocation. The lower limit of the relocated hypocenters corresponds to that of the aftershock distribution. The hypocenter of the main shock was located near the lower limit of the relocated hypocenters. We could not find the configuration of the earthquake source faults from the relocated hypocenters, because the hypocenters were distributed over the entire region. The other region that we studied is the southern part of the Yamagata Basin fault zone, where seismicity is occasionally active in small clusters. We relocated 206 hypocenters by the master event method and the DD method. The hypocenters relocated by the DD method gathered in very small clusters with a size of about 400 m. Neither clusters nor hypocenters within each cluster formed planes. Therefore, we could not guess the geometry of the subsurface faults. If we assume that the subsurface fault extends along the outer rim of the hypocenter distribution, the fault plane inclines by about 75 degrees in the shallow part and is nearly horizontal at 10 km in depth.抄録全体を表示PDF形式でダウンロード (6204K) -
関口 渉次2008 年 61 巻 1 号 p. 11-26
発行日: 2008/08/31
公開日: 2013/09/10
ジャーナル フリーWe developed a simple method to determine epicenters of earthquakes by grid search using only the arrival time order of seismic waves at several observation stations. A target area is divided into small square areas. For each epicenter in the center of the area, a series of stations ordered by the epicentral distance is calculated. When a seismic event occurs and the observed station series sorted by arrival time is obtained, we search for the calculated series of the same order. The corresponding epicenter location is adopted. Generally, the calculated data are voluminous, so the search requires much time. In order to reduce the searching time, we use a UNIX file structure, of which the directory is a station code name. The station code names from the first to the last of the station sequence are assigned to the directory names from the root to the end. The epicenter data is saved in a file in each directory. This implementation reduces the searching time. The method was applied to the Hi-net P arrival time dataset. The mean difference of the estimated epicenter and that of the Hi-net hypocenter catalogue of all events around Japan is 0.609 degrees, when there is a maximum of 20 matching stations. The mean difference of selected events in the Chubu area, central Japan, is 0.076 degrees. The mean difference of events matching the given maximum station number only, are 0.165 degrees and 0.015 degrees, respectively, and are one fifth and one fourth of those obtained using only two stations. The mean difference can be efficiently reduced by increasing the maximum station number up to 10. It is possible to make the mean difference smaller by taking the disorder of the station sequence in the matching algorithm into account. A grid interval of 0.01 degrees is small enough for this dataset. An equation relating the arrival time error and estimated epicenter error is derived. The estimated epicenter error has the same order of amplitude as that obtained above in the Chubu area.抄録全体を表示PDF形式でダウンロード (42072K)
寄書
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—プレート間地震か海洋プレート内地震か?—石橋 克彦, 原田 智也2008 年 61 巻 1 号 p. 27-32
発行日: 2008/08/31
公開日: 2013/09/10
ジャーナル フリーPDF形式でダウンロード (1161K)
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