水域大地电磁测深中水体对电磁场的影响

通过研究层状介质条件下水面与水底电磁场的关系,计算了电磁场的衰减关系式,获得水体对电磁场信号产生的衰减规律和在电磁信号分离采集的水域大地电磁测深勘探中对实测数据的改正方法。研究结果表明:频率越高、水体的电阻率越低,电磁场信号衰减越严重,但水体对电场信号和磁场信号的衰减特征不同,在同等条件下,磁场信号的衰减幅度远大于电场的衰减幅度,且受影响的频率范围也较宽,电场信号的衰减主要取决于水体本身的电阻率和深度,而磁场信号的衰减不仅与水体本身的电阻率、深度有关,还与水体下方介质特征有关,水下介质的电阻率越高,磁场的衰减越严重;在电磁信号分离采集的水域电磁测深勘探中,水域影响可忽略的条件是:使用MT法时水体深度应小于3 m,使用CSAMT法时水体深度应小于2 m。

Liquid effect upon electromagnetic fields in water area MT exploration

By studying the relation of electromagnetic fields and impedance of sill like medium between water surface and water floor,we have gained the attenuation 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 the same condition,and the frequency effect 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 MT exploration of electromagnetic signal sampling is as follows: the water depth is less than 3m in MT,2m in CSAMT.