MT重复测量在地震中短期预报中的应用──祁连山中段MT剖面监测研究

APPLICATION OF THE MT REPEATED MEASUREMENTS TO THE MEDIUM AND SHORT TERM PREDICTION OF EARTHQUAKE──MONITORING AND STUDYING A PROFILE IN THE MIDDLE SEGMENTOF QILIAN MOUNTAIN BY MT

本文研究了青藏高原北缘第一个长约４００ｋｍ的ＭＴ监测剖面上所获得的５次５－７级地震前后的资料。着重分析了在相当于大陆多震层深度范围内壳内介质的多种ＭＴ参数（视电阻率、相位、主轴方位角、扭曲度等）．这些ＭＴ参数在大范围内的同步－同相变化和局部区域之间的超前、滞后变化、相对变化幅度随震中距增大而衰减的特征，可能分别对应着构造孕育型大震的地区性场兆和构造运动型强震的区域性场兆，形成了地震活动大背景叠加小背景的一种链式关系。运用＂ＭＴ监测优显参数＂进行择优监测，将可能为大陆地震的震源物理发展过程和中短期预报提供丰富可靠的判据。

This paper deals with the newest data to do some researches on the earthquake prediction by MT repeated measurements. The data are from the first MT monitoring profile about 400km long in north margin of Qinghai-Tibet Plateau. Five earthquakes of M 5 to M 7 occurred during monitoring along the profile. After studying several MT parameters of the time and space domains on the basis of the error analysis, we found the perfected parameter of the MT monitoring and the perfected frequency range of the MT monitoring. During the activity of great earthquakes accompanied by strong earthquakes and at the depth equal to that of most continental earthquakes (between 10km and 20km from surface), the apparent resistivity of the measurement coordinate axis, apparent resistivity of the main axis, apparent resistivity of the real part and apparent resistivity of the imaginary part all show that the electroconductibility of the media changes in form of drop-rise-recovery,and the skewness and azimuth of the main axis show that the cross heterogeneity of electricity is abated apparently. At the same time, the synchronous and same-phase variations of the MT parameters in wide range might correspond to the regional precursors of great tectonic earthquakes. The lead and lag variations of the MT parameters between local regions, the relative variation amplitude declines as the distance from the focus increases, might correspond to the regional precursors of the strong earthquake which is caused by the movement of the structures. This forms a chain-like relationship in which large background of seismicity is superposed on it small background. The cause about the case has been studied in detail.Monitoring of perfected MT profile can provide rich and reliable criteria for development processes of continental earthquakes and mid- and short-term earthquake prediction.