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

用声脉冲透射法测量了干岩和饱水岩中的地震波速度。我们不仅能够观察到第一发射回波（第一到达），而且还能够观察到由岩石样品和换能器设备之间的声阻抗对比产生的反射回波（第二到达）。然后，我们从第一和第二到达的岩石样品中确定精确的地震速度和品质因子（Q）。这里使用的岩石样品是蛇纹岩，花岗岩和叶蜡石。岩石样品中的速度和Q值都随水的加入而降低。当速度最多降低2%时，Q降低超过50%。Q对流体的存在非常敏感。结果表明，地震Q值是研究地球低Q带流体的有力工具，我们还测定了斜长角闪岩在800℃、1GPa下的速度和Q值。斜长角闪岩样品在1GPa下的固相线为700℃，因此，研究了部分熔融对速度和Q值的影响。在固相线温度以上，熔体分数的增加导致速度和Q的快速下降。结果表明，火山下方的下地壳低速低Q带存在部分熔融。

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.