A Practical Magnetotelluric Method and Its Application in Taiwan: Instrumentation

Author: Yih Jeng(Department of Earth Sciences, National Taiwan Normal University)

Abstract：

The magnetotelluric recording instrument is a deliberately designed electronic system to record the natural magnetic fluctuations and the induced extremely weak terrestrial current. The magnetometer chosen must be capable of measuring the X, Y, and Z components of the mag-netic field. A high input impedance d.c. potentiometer is strongly recommended for sensing the electric field. The most important parts of the terrestrial current measurement are the non-polarizing electrodes which can eliminate the spurious potential created by the electrochemical polarization of the electrodes. Furthermore, the electrodes must be carefully coupled to the ground to avoid the instability of the measurement.
Another critical factor in a magnetotelluric survey is the selection of the energy passband. The data should be recorded at different sampling rates for varying sounding depths. A low-cut filtering of the data before A/D conversion may be employed to avoid the saturation of the converter before the high frequency signal can be registered.
The most troublesome problem in conducting magnetotelluric field work in Taiwan proba-bly comes from environmental factors like the dense population, high man-made noise, and pol-lution. However, the magnetotelluric data collected in this area may provide some interesting information which could qualitatively determine the types of environmental pollution.

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