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前身誌
61 巻, 2 号
選択された号の論文の5件中1～5を表示しています
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論説
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高橋 千佳, 盛川 仁, 駒澤 正夫, 関口 春子, 澤田 純男2008 年 61 巻 2 号 p. 33-48
発行日: 2008/12/31
公開日: 2013/09/10
ジャーナル フリーDestructive earthquake (MJ 6.8) occurred on October 23, 2004 in the Niigata-ken Chuetsu area. Many active foldings are found in this area, and it is known that the subsurface structure is complex. In case we simulate the earthquake ground motions during the main shock in such a complex area, we need detailed information with respect to the subsurface structure. This kind of information, however, is not provided enough currently. Therefore, we carried out the gravity survey around Chuetsu area and estimate a 3-D shape of the upper boundary for the gravity basement. Through the comparison of the proposed model of the gravity basement and the results from some previous researches, we can conclude that the proposed model is improved by the newly observed gravity data. Furthermore, to discuss the validity of the proposed model, we perform two simple numerical simulations of the earthquake ground motions: one is based on the proposed basement model and the other, based on a model estimated using existent gravity data without our contribution. As a result, the proposed model can provide better explanation of the earthquake ground motions than the model from the existent gravity data.抄録全体を表示PDF形式でダウンロード (4987K) -
大滝 壽樹, 伊藤 忍, 加野 直巳, 横倉 隆伸, 山口 和雄2008 年 61 巻 2 号 p. 49-59
発行日: 2008/12/31
公開日: 2013/09/10
ジャーナル フリーA small aftershock of the 2003 Northern Miyagi earthquake was observed during the seismic reflection survey in 2005 which was carried out near the source fault of the 2003 event. The hypocenter of the aftershock determined by the Japan Meteorological Agency (JMA) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) is close to the survey lines and lies in a plane distribution of other aftershocks. Using the observed arrival times in the reflection survey stations in 2005 and the seismic structure determined by using the previous survey in 2003, we determined the hypocenter location of the aftershock. Our hypocenter located in an about 1.6km northwest and about 8km shallower position compared with the hypocenter determined by the JMA and MEXT. The relocated hypocenter is close to the deeper extension of the Asahiyama flexure. We installed one 3-component seismograph nearby during the survey. The observed S-P time of the event at the seismograph can be explained by this hypocenter. The hypocenter determined by the JMA and MEXT is too far from the seismograph to explain this S-P time. Previous reflection surveys show a 2∼3km thick sedimentary layer in the west of the Sue Hills, which area contains this survey territory. A previous gravity survey also suggests this heterogeneous structure extends to a wider area. The heterogeneous structure may cause eastward and deeper bias of the hypocenters estimated by using laterally homogeneous velocity models which have a higher velocity than those estimated from the reflection surveys at shallow depth. This supposed mislocation is consistent with our results.抄録全体を表示PDF形式でダウンロード (2628K) -
平塚 晋也, 佐藤 魂夫2008 年 61 巻 2 号 p. 61-75
発行日: 2008/12/31
公開日: 2013/09/10
ジャーナル フリーWe investigated how the multiple inverse method developed by Yamaji works for the focal mechanism data. A numerical experiment with artificial data revealed that the stresses obtained for the focal mechanism data including auxiliary fault planes agree with those for the data consisting only of actual fault planes. Another numerical experiment showed that the method can retrieve the plural stresses when applied to artificial data that consist of focal mechanisms originating from different stresses. When applied to the focal mechanisms of earthquakes in and around the rupture zone of the 2004 Sumatra-Andaman earthquake, the method could determine the stresses that were not resolved in the previous study, thus allowing us to discuss the tectonic stress field in more detail. We proposed an objective criterion for determining the significant stresses from among the plural inverted solutions. Although the criterion still needs to be refined, we consider that it provides a useful tool for evaluating the relative significance of the plural stresses inverted by the multiple inverse method.抄録全体を表示PDF形式でダウンロード (11267K) -
岡本 響, 大倉 敬宏, 瀬野 徹三2008 年 61 巻 2 号 p. 77-90
発行日: 2008/12/31
公開日: 2013/09/10
ジャーナル フリーSince dehydration embrittlement of oceanic crust and mantle in a subducting slab is considered to be responsible for the occurrence of intermediate-depth earthquakes, it is very important to know the location of these earthquakes; within the oceanic crust and/or the slab mantle. Usually in Southwest Japan, crustal earthquakes in the Philippine Sea plate (PHS) are associated with deep low frequency tremor. In order to determine the locations of intraslab earthquakes of the PHS in central and southern Kyushu, Japan, we examined existence of seismic waves guided by the oceanic crust, and we applied the Double-Difference method for relocating the interplate and intraslab earthquakes occurring in the study area. The results are as follows. (1) Throughout the study area, waveform analysis and hypocenter determination show that intraslab earthquakes occurred within the slab mantle. (2) From waveform analysis, we found that in the northern part of the study area, where no deep low frequency tremor is observed, some intraslab earthquakes occurred within the oceanic crust. (3) It is not clear whether earthquakes occurred within the oceanic crust in the southern part of the study area. Therefore, central Kyushu is unusual region in Southwest Japan, where dehydration takes place in the oceanic crust but it is not associated with deep low frequency tremor above the slab.抄録全体を表示PDF形式でダウンロード (5334K)
寄書
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宮武 隆, 三宅 弘恵, 木村 武志, 隅谷 謙一2008 年 61 巻 2 号 p. 91-97
発行日: 2008/12/31
公開日: 2013/09/10
ジャーナル フリーPDF形式でダウンロード (7361K)
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