关键词: 超低频/极低频, 大地电阻率, 地球电磁法

Abstract: Since the last decade, the applicability of source-controllable powerful Super Low Frequency/Extremely Low Frequency (SLF/ELF) electromagnetic waves to the reconnaissance of resources and monitoring of earthquake has attracted great attention of the geophysical communities for its high precision and vast area of service region. It has become a new and prospecting field of research. By using this technique, the signal of high precision can be transmitted and received at each frequency under control. The observed data can then be analyzed by using correlation analysis technique. This will greatly enhance the signal-to-noise ratio and the precision of the observed data even in strong noise area. The signal can penetrate down to several dozens kilometers depth, so that it is widely applied to the reconnaissance of resources, detection of subsurface nuclear waste, environmental research, as well as the monitoring and prediction of earthquake. The construction of a high power (not less than 100～200kW) SLF/ELF transmitter is one of the most important bases of the system used for geophysical investigation and application. The analysis has shown that the height of earth resistivity of the antenna site plays a key role in increasing the efficiency of the transmitter. The earth resistivity bears a close relation with lithology and tectonic structure of the area. It is suggested, therefore, that the high resistivity of the antenna site is the necessary condition for the transmission of effective SLF/ELF electromagnetic waves. The measurement method and strategy for ELF/SLF antenna site selection are proposed in this paper as well.

Key words: Super low frequency/Extremely low frequency, Earth resistivity, Geo-electromagnetic method