摘要
在垂直地面方向上,来自不同深度的两个电磁波信号到达地面的群时延差(时差),在给定频率下,只与两信号间地层的电导率和厚度有关。一般认为在地震前,深层电导率会出现异常变化。电导率的这种异常变化可通过群时延差的异常变化测知。故群时延差的异常变化可用于短临地震预测。基于上述想法,并将50 Hz工频当作载波看待,成功研制出了电场和磁场探测仪,实现了电场传感器,磁场传感器和整机的小型化,实现了点式探测。仪器使用频率为1 Hz和0.2 Hz,在地面接收自然信号,探测仪输出波形清晰,易于辨认。本文介绍了用群时延差测定深层电导率变化的基本原理,群时延差探测仪的结构及其在地面接收到的自然信号波形和有用信息的识别方法。讨论了深层是否能有小于等于1 Hz的电磁波到达地面并可被接收到的问题。
The group delay difference (time difference) between two electromagnetic signals at a given fre-quency, which are located along the same vertical line but at different depths and reach the ground, depends only on the electric conductivity and the thickness of the strata. It is believed that the conductivity of the deep layer undergoes abnormal variations just before earthquakes. Such conductivity variations can be detected in terms of the abnormal changes of the group delay dif-ference, and thus the abnormal changes of the group delay difference may be used for short-term and imminent earthquake prediction. Based on this idea, we have developed an electric field de-tector and a magnetic field detector. The regular alternating signal of 50 Hz is treated as a carrier wave so as to achieve a miniaturization of the electric field sensor, the magnetic field sensor, and the detector as a whole, and a point-by-point probing as well. The operation frequencies of the detector are set to be 1 Hz and 0.2 Hz, and natural signals are received on the ground with clear, easily identifiable output waveforms. This paper introduces the basic principle of applying group delay difference to measure the conductivity variations of deep layer, the structure of the group delay difference detector, the natural signal waveform received on the ground, and the recognition method of useful message. Also the paper discussed the problem of whether electromagnetic waves in the deep layer with frequency less than or equal to 1 Hz are able to arrive at the ground and to be received.
