Analysis of Electromagnetic Field Affected by Liquid in Water Area Magnetotelluric Exploration

摘要

By studying the relation of electromagnetic fields and impedance of sill like medium between water surface and water floor, we have gained the attenuated coefficient and the attenuation law of electromagnetic fields in water area. It is obvious that the signals are attenuated worse when the frequency increases, but the liquid attenuation characters upon electric field and magnetic field are different. First, the attenuation amplitude of magnetic field is far greater than electric field in same condition, and the frequency range is wider. Second, the attenuation of electric field not only lies on mostly the character of liquid self (the depth and resistivity of liquid), but also on the media property below the water, that is, the higher the resistivity is the more severe the attenuation of the magnetic field, the attenuation of magnetic field relates to the characters of liquid medium. The condition in which the water effect can be neglected in water magnetotelluric sounding (MT) exploration of electromagnetic signal sampling is as follows: The water depth is less than 3 m in MT and 2 m in CSAMT.