An Experimental On Rock Deformation And Electromagnetic Emission

Because of the urgent demand of earthquake disaster reduction, the electromagnetic emission(EME) observation and research has become one of the focused issues in seismology. Many scholars of China, Russia, Japan and Greek have attempted or are trying some predictions to earthquakes in terms of EME signals, such as earth resistivity, natural current and preseismic electromagnetic radiation etc. However, the earthquake processes inside the crust is very complicated and the EM mechanism has not been understood reasonably and clearly. The success ratio of prediction with EM signals is not doubtless. In order to deal with the generative mechanism and the variation of EM signals prior to an earthquake, a lot of researches about EM activity during rock fracture have finished under the controlled conditions in laboratory.Although the work on EM signals has made progress greatly, there are many doubtful points still. The hackneyed problem is the experiments from different laboratories are so variable or even competing that it is too difficult to confirm. One of the key reasons is the features of the experiment systems in laboratories are different from each other.On the other hand the design of the experiments is different also.A new set of the EM experiment system is built up in our laboratory, which receives the EM signals of rock fracture more effectively and loads a specimen in a low noise method. With the system further researches on the features and mechanisms of EM signals in deformation process are enabled. The results in this thesis are based on this system.The research progresses of this work are summarized as follows:(1) A set of the EM signals observation system fitting acquisition of EME signals during rock deformation and rupture in lab is developed. The parameters of the system are determined thoughtfully. It is the first stable and applied EME experiment system in our laboratory.(2) By using an artificial percussion the EM signals from five type of rocks are measured. They are quartz crystal, granodiorite, sandstone, marble and gabbro. The signal amplitude and frequency are determined. The results show that with a sudden mechanical vibration, regardless can whether the rock contains quartz, a strong enough electromagnetic radiation signal can be generated and received by the new system. The amplitude from quartz crystal is the strongest and the frequency highest.(3) Three kinds of loading mode are employed to produce deformation and fracture of rocks. They are uniaxial compression, three-point bending and self-expansion burst test. Five type of rock samples, i.e.adamellite, granodiorite, sandstone, marble and gabbro, are used in the experiment. For different types of rocks in the same loading mode, the larger the quartz grains size the stronger the amplitude of the EM signals are and higher the frequency. May be it means that a rock including high contents of piezoelectric mineral is more capable of generating electromagnetic signals. For the same rock samples at different loading modes, uniaxial compression rupture produced a largest number of strong signals. It suggests that the mechanical deformation or rupture of rock have a strong control effect on EM signals also. Generally speaking the failure process under uniaxial compression includes more compressively shearing friction events than the three-point bending and self-expanding. It implies that the mechanism of a large number of electromagnetic signals occurred in compression is friction and fracture rather than only piezoelectric effect.(4) There is a temporal significant correlation between the electromagnetic radiation signals and acoustic emission signals during rock fracture. The occurrence of electromagnetic signal and acoustic emission signals in joint observation is synchronized. It can be speculated that the electromagnetic signals are closely related to acoustic emission signals. To make an intensive study of the relation between individual electromagnetic signal and single acoustic emission signals, more refined experiments are needed and stricter criteria should be established.(5) It is unlikeliness to explain electromagnetic radiation signals generated by the process of rock failure only with one simple mechanism. In a variety of typical experiments, the rock composition and different dominant deformation processes are quite different, but strong electromagnetic signals take place without exception. Therefore it can be suggested that most of the mechanisms for EM signals proposed by scholars, such as piezoelectric effect, friction and macroscopic crack propagation, are present possibly. The mechanism should not be simply explained by only one model and it is not necessary to pursue a unique solution。...