Microwave Emission of Rock Change with Compressive Stress: Experiments and Physics

Abstract

The stress-induced additional microwave emission of rock is of great importance and potentialities for studying geo-hazards and monitoring thermal anomalies in seismic prone zones with satellite remote sensing. Many laboratory experiments have illustrated obvious variation of microwave emission in process of rock loading to fracturing, but the underlying mechanism is not clear. By using a C-band microwave radiometer (6.9 GHz) and an open end resonant probe, the variations of microwave brightness temperature (MBT) and microwave dielectric property of rock specimens being axially compressively loaded are experimentally investigated, respectively. The experimental results show 1) the MBT of rock specimen increase obviously with increasing loads at elastic deformation stage; 2) the dielectric constants of rock specimens decreases by 0.03 ~ 0.05 with increasing compressive stress, of which the induced variations of MBT is basically consistent with the results from MBT observations. Therefore the alteration of rock microwave dielectric permittivity at elastic deformation stage is presented to be the basic mechanism of rock microwave emissivity change, and thus lead to the variation of rock MBT. This study provides an electromagnetic base for analyzing stress-induced rock microwave emission and for monitoring crust stress filed alteration process (such as in process of tectonic earthquake preparation) using satellite microwave remote sensing data.