Velocity and Q measurements on rock-water system at high pressure and temperature using a large volume cylinder

采用声脉冲传输技术测量了干岩和含水饱和岩的地震速度。我们不仅可以观察到第一透射回波（第一到达），还可以观察到岩石样品与换能器之间的声阻抗对比产生的反射回波（第二到达）。然后，我们在第一次和第二次到达的岩石样本中确定准确的地震速度和质量因子(Q)。这里使用的岩石样本是蛇纹岩、花岗岩和叶蜡岩。岩石样品中的速度和Q随水的加入而减小。虽然速度最多减少2%，但Q减少了50%以上。Q对流体的存在非常敏感。这一结果意味着地震Q是研究地球低Q带流体的有力工具。我们还测定了角闪岩在800℃、1gpa下的速度和Q值。角闪石样品的固相温度为700℃，温度为1 GPa；因此，研究了部分熔体对速度和Q的影响。在固相温度以上，熔体分数的增加导致速度和Q值的迅速下降。结果表明，在火山下方的地壳下低速和低Q带存在部分熔体。

Seismic velocities in dry and water-saturated rocks were measured by acoustic pulse transmission technique. We are able to observe not only first transmitted echoes (first arrivals), but also reflected echoes (second arrivals) generated by the acoustic impedance contrast between the rock sample and the transducer device. We, then, determine accurate seismic velocities and quality factors (Q) in rock samples from both the first and second arrivals.Rock samples used here were a serpentinite, a granite and a pyrophyllite. Both velocity and Q in rock samples decrease with the addition of water. While velocity decreases at most 2%, Q decreases more than 50%. Q is very sensitive to the presence of fluid. The results mean that the seismic Q is a powerful tool to study fluids in the Earth's low Q zone.We have also determined velocity and Q in amphibolite to 800℃ at 1 GPa. The solidus of the amphibolite sample is 700℃ at 1 GPa ; therefore, the effect of partial melt on velocity and Q was studied. Above the solidus temperature, increases in melt fraction cause rapid decreases in both velocity and Q. The results indicate the presence of partial melt in the lower crustal low velocity and low Q zone beneath the volcanoes.