Elastic wave velocity and Poisson's ratio of shallow crustal seismogenic zone

地震层析成像研究的最新进展表明，岛弧各地区的地壳和上地幔存在地震低速异常。此外，理论研究表明熔体/流体对Vp和Vs的显著负面影响作为熔体/流体分数及其几何特征的函数。这些研究共同表明，熔体/流体相的存在，在这些地区定义的低速异常。地震层析成像研究还表明，某些低速异常区在空间上与在弧壳相对较浅的水平上观察到的孕震带有关。为了评估在与火山弧壳中下地壳条件相当的高温和高压下熔体/流体对地震速度和岩石泊松比的影响，我们发展了一种新的实验方法，使我们能够在高压下（高达1000 ℃）同时测量岩石中的Vp和Vs。 ...更多信息 o 900℃）和温度（高达1 GPa）。利用这种新的实验方法，我们测量了各种下地壳和上地幔岩石，包括角闪岩，辉长岩，橄榄岩，英云闪长岩，这是收集从Tanzawa，一野megata，高岛，和Kohistan的Vp和Vs。我们的数据表明，Vp和Vs显着降低，随着温度的升高，并高度依赖于岩石样品中的熔体/流体比例。利用实验数据和地震层析成像图像，建立了伊豆弧壳北方部分和本州弧壳东北部的岩石学模型。我们的数据表明，伊豆弧的1.6km Vp中地壳层是由角闪石-听力长英质岩（英云闪长岩）。数据还表明，东北本州弧的下地壳由角闪石轴承辉长岩。地震层析成像研究所定义的低速异常区被解释为具有相当数量的熔融相的区域。少

The recent development in seismic tomographic study has demonstrated presences of seismic low velocity anomalies within crust and upper mantle beneath various areas of island arcs. In addition, theoretical studies have suggested significant negative effects of melt/fluid on Vp and Vs as a function of melt/fluid fraction and its geometric characteristics. These studies collectively suggest a presence of melt/fluid phase in such areas defined by low velocity anomalies. The seismic tomographic studies also suggested that some areas with low velocity anomalies are spatially associated with seismogenic zones observed at relatively shallower level of arc crust.To evaluate the effect of melt/fluid on seismic velocities and Poisson's ratio of rocks under high temperatures and pressures comparable to the middle to lower crustal conditions of volcanic arc crust, we developed the new experimental method that enable us to make simultaneous measurements of Vp and Vs in rocks at high pressures (up t … More o 900℃) and temperatures (up to 1 GPa). Using this new experimental method, we measured Vp and Vs of various lower crustal and upper mantle rocks including amphibolite, gabbro, peridotite, and tonalite, which were collected from Tanzawa, Ichino-megata, Takashima, and Kohistan. Our data demonstrate that Vp and Vs significantly decrease with elevating temperature and highly depend on melt/fluid proportion in the rock sample. The data also suggest that phase the transformation of high-low plagioclase is an additional factor, which significantly controls seismic velocity of crustal rocks at middle to lower crustal levels.Employing the present experimental data and the seismic tomographic images, we constructed petrological models for the northern part of Izu arc crust and the northeastern Honshu arc crust. Our data suggest that the 〜6 km Vp middle crustal layer defined for the Izu arc is composed of hornblende-hearing felsic rock (tonalite). The data also suggest that the lower crust of the northeastern Honshu arc consists of hornblende-bearing gabbro. The area of low velocity anomalies defined by the seismic tomographic studies are interpreted as a zone having considerable amounts of melt phase. Less