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61 巻, 3 号
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論説
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鏡味 芳宏, 渡辺 了2009 年 61 巻 3 号 p. 99-111
発行日: 2009/03/30
公開日: 2013/09/10
ジャーナル フリーShallow crustal materials in the Atotsugawa fault area were inferred based on measured elastic wave velocities of various rocks sampled in this area. The Atotsugawa fault is situated in the Niigata-Kobe Tectonic Zone, where large crustal deformation has been observed by a dense GPS network. Active microseismicity has been observed along the fault. The subsurface structure of this area has been geophysically investigated in search of structural factors in observed tectonic activities. Elastic wave velocities of crustal materials are required to infer constituent materials and physical conditions from geophysical data. Based on previous geological studies, Hida granitic rocks, Hida metamorphic rocks, a Tedori-group sandstone and a Nohi rhyolite were sampled as typical rocks in this area. Measurements of elastic wave velocity were conducted at room temperature under confining pressures up to 180MPa. Tedori-group sandstone and Nohi rhyolite show low compressional wave velocity of 5.6-5.7km/s at 180MPa. Compressional wave velocity is 6.2-6.3km/s in Hida granitic rocks, while 6.0-6.1km/s in metagranites. The higher velocity of Hida granitic rocks is attributed to the abundance of hornblende. Gneisses show a wide range of the compressional wave velocity of 6.0-6.7km/s, reflecting the variation in mineralogy. Samples rich in hornblende or calcite tend to show higher compressional wave velocity. On the other hand, a sample rich in biotite shows lower velocity. The sandstone has a low velocity ratio Vp/Vs around 1.6, while other rocks have Vp/Vs of 1.7-1.8. Considering the previously investigated temperature dependence of the compressional wave velocity, we infer the subsurface lithology around the Atotsugawa fault from the seismic velocity structure. The high velocity body beneath the Atotugawa fault is mostly composed of gneisses. Hida granites and/or metagranites could be minor components. At 30km south from the fault, the Nohi rhyolite and Hida granitic rocks are expected to coexist at the depth of 3km. The high velocity body at 6km is mostly composed of Hida granitic rocks. Considering the continuity of the high velocity body, gneisses could coexist with granitic rocks抄録全体を表示PDF形式でダウンロード (3775K) -
—東海スロースリップと2004年紀伊半島南東沖の地震の余効変動—水藤 尚, 小沢 慎三郎2009 年 61 巻 3 号 p. 113-135
発行日: 2009/03/30
公開日: 2013/09/10
ジャーナル フリーWe investigated the transient crustal deformation in the Tokai district, central Japan, based on the GPS data in 2000-2008. Our modeling showed that observed transient deformation in the Tokai district can be explained by three different mechanisms, slow slip on the plate interface, viscoelastic response and an afterslip following the 2004 off southeast Kii peninsula earthquake. In our modeling, we first evaluated the effect of postseismic deformation due to the viscoelastic response of the 2004 off southeast Kii peninsula earthquake, and obtained the reasonable value of viscosity 1.0×1019 Pa·s. Then we estimated the afterslip model of the 2004 off southeast Kii peninsula earthquake, and obtained that the time constant of the postseismic deformation caused by the afterslip is 62.65 days. After removing the viscoelastic response and the effect of afterslip from original transient deformation, we modeled this transient deformation as a slow slip on the plate interface, which we call here as Tokai slow slip event. Our result revealed that the Tokai slow slip which occurred mainly under the Lake Hamana ended in July 2005. The maximum slip of this event was estimated at 25cm under the Lake Hamana. This maximum slip accounts for the backslip accumulated in the past 14 years, assuming that the backslip rate has been constant. The total moment release was equivalent to that of an Mw 7.1 earthquake. On the other hand, the aseismic slip still continues in the northeast region of the Lake Hamana at the same rate as that before July 2005. The maximum slip in this region since July 2005 reaches 5cm, and total moment release is equivalent to that of an Mw 6.5 earthquake.抄録全体を表示PDF形式でダウンロード (10538K)
寄書
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塩原 肇, 金沢 敏彦2009 年 61 巻 3 号 p. 137-144
発行日: 2009/03/30
公開日: 2013/09/10
ジャーナル フリーPDF形式でダウンロード (2439K) -
伊尾木 圭衣, 谷岡 勇市郎2009 年 61 巻 3 号 p. 145-148
発行日: 2009/03/30
公開日: 2013/09/10
ジャーナル フリーPDF形式でダウンロード (1317K)
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