深海底から採取した蛇紋岩の弾性波速度測定：予察

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タイトル別名
  • Preliminary results of elastic wave velocity measurements on a serpentinite obtained from the deep-sea floor
  • 深海底から採集した蛇紋岩の弾性波速度測定--予報
  • シンカイテイ カラ サイシュウ シタ ジャモンガン ノ ダンセイハ ソクド ソクテイ ヨホウ

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Elastic wave velocities were measured on a deep seafloor serpentinite sample at room temperature and confining pressures of up to 180 MPa, using a high-pressure apparatus at University of Toyama. The sample was collected from a dredge site D17 at the Godzilla Megamullion, Parece Vela Rift, Phillipine Sea during the cruise KR07-02 (R/V Kairei). The serpentinite sample has the density of 2.37 g/cm3 and consists mainly of lizardite, chrysotile and magnetite, showing a banded structure with a moderately developed lineation and foliation. Mutually orthogonal axes were set for velocity measurements; the x-axis is parallel to the lineation, and the z-axis normal to the foliation. Lizardite mainly has a mesh texture, whereas fibrous chrysotile fills veins, most of which are subperpendicular to the lineation. The compressional wave velocity at 180 MPa is the fastest (4.56 km/s) in the y-axis direction, the slowest (3.97 km) in the direction parallel to the lineation (x-axis direction), and intermediate (4.25 km/s) normal to the foliation (z-axis direction). The azimuthal anisotropy is 13.85% at 180 MPa. The shear wave velocity at 180 MPa is 2.07~2.35 km/s. The shear waves oscillating parallel to the yz-plane have the fastest velocity, and that normal to the yz-plane the slowest. The polarization anisotropy is thus strong along the y- (9.35%) and z- (12.24%) axes, whereas weak along the x-axis (1.39%). Based on microstructural examinations, observed velocity anisotropy may be mainly controlled by the orientation of chrysotile veins rather than the banded structure.

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