Simultaneous measurement of electrical and mechanical properties of rock at high temperatures and pressures

最近的观测研究揭示了地壳P波和S波速度（Vp和Vs）、Q值和电导率的详细结构。然而，我们不能从观测结果中提取足够的信息，岩石的断裂特性。为了获得这些信息，同时测量岩石的电学和力学性质是很有帮助的，高温高压下岩石电导率的测量需要在岩石试样上涂上金属护套。为了在这种情况下测量电导率，我们设计了一个带有保护环的电极模块。通过使用保护环和中心电极，主要沿沿着金属护套流动的电流与通过岩石试样的电流分离。通过数值计算，得到了流入保护环和中心电极的电流与样品真实电导率之间的关系。使用新开发的模块，我们测量了温度高达250度，压力高达250 MPa，频率范围从1 Hz到1 MHz的岩石电导率。例如，我们发现，日高的泥质角岩具有明显的温度依赖性;电导率在75度左右显示出最低值。

Recently observational studies have revealed detailed crust structure of P-and S-wave velocities (Vp and Vs), Q value, and electric conductivity. However, we cannot extract sufficient information about fracture properties of rock from the observational results. In order to get such information, simultaneous measurements of electrical and mechanical properties of rock is helpful.Measurement of electric conductivity of rock at high temperature and pressure needs metal jacket, with which we coat the rock specimen. In order to measure electric conductivity in this situation, we designed an electrode module with a guard ring. Electric current which mainly flows along the metal jacket is separated from the current through the rock specimen, by using the guard ring and center electrode. We numerically calculated the electric currents flowing into the guard ring and center electrode, and obtained the relation between the measured current and the true conductivity of the specimen. Using the newly developed module, we measured rock conductivities at temperatures up to 250 degree, pressures up to 250 MPa, and frequencies ranging from 1 Hz to 1 MHz. We found, for example, that pelitic hormfels in Hidaka had a clear temperature dependence; the conductivity showed the lowest value around 75 degree.