Many studies have confirmed that the microwave radiation of rock materials will change with compressive stress and pore water. However, how the presence of pore water in rock volume influences the stress-induced change in microwave radiation ( $\Delta T_{B}$ ) is not clear. In this study, both the air-dry and humid (partially saturated) sandstone specimens were loaded compressively and the C-band (6.9 GHz) microwave radiometer was used to investigate the change of $T_{B}$ and the differences of $\Delta T_{B}$ . The experimental results illustrated that the presence of pore water in sandstone promotes significantly the relationship between the positive $\Delta T_{B}$ and the applied compressive load. On the basis of radiative transfer theory and effective dielectric constant model of multiple-phase media, we found that $\Delta T_{B}$ of sandstone mainly results from the compressive stress distributed on mineral grains, which is able to reduce the dielectric constant of minerals and lead to the increase of microwave radiation. For dry sandstone, the distribution of compressive stress on minerals is mainly controlled by grain contact, while for humid sandstone, the pore water plays an important role in applying uniform pressure on grain surface and reducing the dielectric constant of grains; thus, the effective dielectric constant of rock volume is sensitive to the applied loads on partially saturated specimen. This study is important for understanding the positive $T_{B}$ anomalies prior to large tectonic earthquakes in condition of ground surface rock partially saturated and is valuable to uncover potential $T_{B}$ anomaly related to seismic activities.

中文翻译：

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部分饱和砂岩压缩应力的实验室微波（C 波段）响应

许多研究证实，岩石材料的微波辐射会随着压缩应力和孔隙水的变化而变化。然而，岩石体积中孔隙水的存在如何影响应力引起的微波辐射变化（ $\Delta T_{B}$ ） 不清楚。在这项研究中，对风干和潮湿（部分饱和）砂岩试样进行压缩加载，并使用 C 波段（6.9 GHz）微波辐射计研究 $T_{B}$和不同之处 $\Delta T_{B}$ . 实验结果表明，砂岩中孔隙水的存在显着促进了正向关系。 $\Delta T_{B}$和施加的压缩载荷。基于辐射传输理论和多相介质的有效介电常数模型，我们发现 $\Delta T_{B}$砂岩的主要作用是分布在矿物颗粒上的压应力，可以降低矿物的介电常数，导致微波辐射的增加。对于干砂岩，矿物压应力的分布主要受颗粒接触控制，而对于湿砂岩，孔隙水对颗粒表面施加均匀压力和降低颗粒介电常数起着重要作用；因此，岩石体积的有效介电常数对施加在部分饱和试样上的载荷很敏感。这项研究对于了解积极因素很重要 $T_{B}$在地表岩石部分饱和的条件下，大构造地震前的异常现象对揭示潜力具有重要意义 $T_{B}$与地震活动有关的异常。