Applicable conditions and effects of remote reference method of magnetotelluric electric field
WANG Peijie1, CHEN Xiaobin2, ZHANG Yunyun2, YANG Jing3, DONG Zeyi1
1. Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China; 3. Linfen Earthquake Monitoring Center Station, Shanxi Earthquake Agency, Linfen, Shanxi 041000, China
Abstract：The remote reference method is effective for processing magnetotelluric （MT） time series data.It is generally believed that magnetic fields yield better effects as reference channels，but electric fields are not suitable as remote reference channels due to their susceptibility to underground structures.Based on actual data processing，this paper explores the utilization of electric fields as reference channels for processing MT data and finds that they perform well in the high-frequency range above 1 Hz but poorly in the low-frequency range.Then，it puts forward a new approach that employs electric fields as reference channels for processing high-frequency data.Fine processing of audio magnetotelluric （AMT） data confirms the validity of electric fields as reference channels in the high-frequency range （> 1 Hz）.Application of this approach to AMT data processing indicates that the results obtained by adopting electric fields as reference channels are comparable to those by utilizing magnetic fields as reference channels，with sound improvement in data processing of AMT “dead band”（1k~5k Hz）.AMT data collection typically involves multiple measurement points sharing a set of magnetic channels，and the electric channel number greatly exceeds that of magnetic channels.Thus，processing of remote reference channel electric fields can significantly improve AMT data processing results and can be popularized as a conventional processing method.Analysis of natural source electromagnetic fields and MT dimensionality parameters shows that the limited influence of high-frequency electric fields on underground structures is the underlying reason for the remote reference channel data effectiveness of electric fields.This research also provides guidance for the location selection of remote reference stations，suggesting that the stations should be situated in areas with simple geoelectric structures to minimize interference of underground electrical structures on natural electromagnetic field signals from the same source as the survey area.
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