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对沉积物底下的海洋岩石圈进行电磁探测是很困难的,因为该层的电阻率比其上复与下伏的结构都要高。有三个方法能够提供这方面的资料: 1)大地电磁法能提供作为频率的函数的阻抗方面的讯息,低到一定程度的低频信号能够穿透大洋。在深海中,此频率的上限为每小时数周。 2)在海底上能够测到一个准静电扬。这个电场是海水流经地磁场的运动形成的电荷所造成的。由于岩石圈在海洋下面提供了一个水流通道,因此其电导率有减弱这个电场的趋势。要解释测量的结果,则需要了解海水运动的空间特性。 3)发射频率约1赫芝的人工电磁源能够在海底上使用。曾在海底上距发射源18公里处检测到通过岩石圈传播的电磁能。检测工作是在该高频段于很低的噪声电平下进行的。给出了整个洋壳的导率分布的估算值。
Electromagnetic detection of marine lithosphere beneath sediments is difficult because of the higher resistivity of the layer than the underlying and underlying structures. There are three ways to provide this information: 1) Magnetotelluric can provide impedance as a function of the frequency of the message, to a certain extent, low-frequency signals can penetrate the ocean. In the deep ocean, the upper limit for this frequency is weeks per hour. 2) A quasi-electrostatic lift can be measured on the sea floor. This electric field is caused by the electric charge created by the movement of seawater through the earth’s magnetic field. Since the lithosphere provides a water flow path under the ocean, its conductivity tends to attenuate this electric field. To interpret the measurement results, you need to understand the spatial characteristics of seawater movement. 3) The artificial electromagnetic source emitting at about 1 Hertz can be used on the sea floor. Electromagnetic energy transmitted through the lithosphere was detected 18 km above the seafloor at the launch site. The detection is done at this high frequency at very low noise levels. An estimate of the conductivity distribution of the entire oceanic crust is given.