Abstract: The electromagnetic method plays an important role in seismic activity monitoring and earthquake prediction and has become one of the important ways for earthquake prediction.During the past decades,many electromagnetic anomalous phenomena at available frequency bands(ELF,VLF,ULF,LF,FM etc.),especially at SLF and ELF bands were observed by scientists before earthquakes,which show that the electromagnetic effects do exist before shocks.Major earthquake may be predicted accurately if the corresponding relation between these electromagnetic anomalies and the physical process in the crust can be proved.In these studies,the objective is the natural electromagnetic field.Because its signal is characterized by instability,low precision and prone to influence of disturbance,especially at the sites with strong noise,the observational data often have low signal-tonoise ratio(SNR).Therefore,its applications are greatly limited.In order to improve the capability of identifying earthquake electromagnetic precursors,researchers must find a new source whose signal has higher stability and precision and wider coverage.In recent years,great progress has been made in the study.Russian scientists firstly applied the artificial SLF/ELF signal to probing the electrical structure of the crust in 1990s,since then,this technique has attracted much attention of geophysicists.Because the artificial SLF/ELF signal can be transmitted high precisely at each frequency under control and has the advantages of strong power,less influence of ionosphere,vast coverage,stable transmission and continuous observation,and the observed data can be analyzed by the correlation analysis technique,the SNR and precision of observed data,even in areas of strong noise,can be greatly enhanced.Measurement results show that in the same setting,the observed signal from SLF/ELF transmitter facility is much stronger than that from natural one,and the apparent resistivity obtained by the former has much higher precision than that by the latter.Therefore,this technique is very suitable for those studies requiring high-precision observational data,especially for earthquake monitoring and prediction.In our country,the study of the SLF/ELF technique started since late 1990s.In this paper,a newly developed SLF/ELF receiver's hardware system scheme,principle,main technical specifications and key technology are introduced in details.Results from a series of tests in lab and in field have shown that the SLF/ELF receiver can be used for observing the artificial SLF/ELF signal with frequency range from 0.1 to 300Hz.

Key words: artificial SLF/ELF signal, observation system, correlation detection, zoom FFT

摘要： 大功率、人工源的超低频/极低频电磁波技术已经成为当今国际地球物理学界瞩目的一个新兴研究领域,采用此方法计算获得的地下介质电性结构具有很高的精度和稳定性,特别适用于地震预测等需要精确观测数据的研究。在中国,从20世纪90年代末开始,开展了基于大功率人工源超低频/极低频技术的方法研究,也开展了该方法在地震监测领域的应用研究,然而对于适用于地震监测应用的观测系统的研究进展比较缓慢。文中介绍了专门用于地震监测应用的超低频/极低频电磁接收机的研发,详细说明了仪器的硬件系统组成、主要技术指标及其关键技术。试验观测结果表明该仪器能满足目前0.1～300Hz频段人工源电磁信号观测的需求。

关键词: 人工源超低频/极低频, 观测系统, 相关检测, 频率细化