岩石破坏过程磁场效应实验研究及其对地震预报的意义

Experimental research on magnetic field variation in rock failure process and its significance for earthquake prediction

地震前岩石圈存在可观测的磁场前兆异常,岩石破坏过程的磁场效应规律却鲜有研究.本文设计建立了岩石破坏磁场效应监测实验系统,测试分析了岩石破坏过程磁场与载荷、声发射、电磁辐射之间的关系,探讨了岩石破坏磁场产生机制与岩石破坏磁场效应对地震预报的意义.结果表明:岩石在受载破坏过程能够产生磁场,磁感应强度与载荷变化存在良好的对应关系.在受载前期,磁感应强度波动增加,受载中后期,磁场强度显著增加;主破坏发生时,磁场强度快速增加并达到最大值.磁感应强度与累积声发射计数平均相关系数达到0.825,呈高度相关,表明磁场变化能够反映岩石的变形破坏阶段和状态.岩石破坏磁场的产生主要与电性变化有关,运动电荷或电流的变化产生了磁场.岩石破坏磁场与电磁辐射同属于电磁信号,磁场是一种极低频、连续、脉冲式的信号,信号频率一般为0~20 Hz;电磁辐射是一种瞬态、阵发性的电磁波,信号频率一般为kHz~MHz.相对于电磁辐射,磁场前兆异常先出现,岩石破坏的磁场监测结果对于评估地震的临震预报具有显著的意义.

There are observable magnetic precursory anomalies in the lithosphere before the earthquake,but there is little research on the magnetic field effect law in the process of rock failure.In this paper,an experimental system for monitoring the magnetic field effect of rock failure is designed and established.The relationship between the magnetic field and the load,acoustic emission and electromagnetic radiation during the rock failure process is tested and analyzed.The mechanism of rock failure magnetic field and the significance of rock failure magnetic field effect on earthquake prediction are discussed.The results show that the rock can generate a magnetic field in the process of load failure,and there is a good correspondence between the magnetic induction intensity and the load change.In the early stage of loading,the fluctuation of magnetic induction intensity increases,and in the middle and late stage of loading,the magnetic field intensity increases significantly.When the main failure occurs,the magnetic field intensity increases rapidly and reaches the maximum value.The average correlation coefficient between the magnetic induction intensity and the cumulative acoustic emission count reaches 0.825,which shows that the change of magnetic field can reflect the deformation and failure stage and state of rock.The generation of rock failure magnetic field is mainly related to the change of electrical property,and the change of moving charge or current generates magnetic field.The rock failure magnetic field and electromagnetic radiation belong to electromagnetic signals.The magnetic field signal is an extremely low frequency,continuous and pulsed signal,and the signal frequency is generally 0~20 Hz.Electromagnetic radiation signal is a transient and paroxysmal electromagnetic wave,and the signal frequency is generally kHz~MHz.Compared with electromagnetic radiation,the magnetic field precursor anomaly appears first,and the magnetic field monitoring results of rock failure are of great significance for evaluating the imminent earthquake prediction of earthquakes.