Electromagnetic signals of a seismic excitation of geolocal structures beneath a sea bottom

S.V. Ershov , I.B. Mikhaylovskaya , O.B. Novik
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引用次数: 3

Abstract

We formulate a mathematical model of generation and propagation of seismo-electromagnetic (EM) signals in the basin of a marginal sea with an arbitrary 2D geological structure of the bottom, including the transfer of seismic and EM energy from lithosphere to hydrosphere and EM emission into atmosphere. In case of a model basin which is a 2D scheme of the central part of the basin of the Sea of Japan, the first magnetic signal is generated in the conductive (0.02 S/m) upper mantle layer M where weak seismic displacements (SD) are supposed to arise at the moment t = 0. The amplitude and duration of a SD were of order of a few centimetres and a few seconds and differ in different simulations. The primary signal from M with the amplitude about 50 pT reaches for the sea bottom at the moment t = 3.5 sec. Magnetic diffusion into the conductive sea water is too slow and thus EM signal in atmosphere originates due to geomagnetic field induction in the vertically moving water column Qs located above the area of the initial contact of the seismic P wave (from M) with the sea bottom. Because of the structure of the seismo-hydrodynamic field and the EM field conjugation conditions at the sea-atmosphere interface the horizontal component B2 of the seismo-hydrodynamic magnetic field is being generated, at first, in a thin water layer under the top of Qs at the sea surface, whereas the vertical component B1 is being generated everywhere in Qs. After the spreading of the magnetic signals, B1 is up to 250 and 150 pT at the sea surface and at the height of 10 km respectively at t = 10 sec Magnetic signals are represented by oscillations of the same low frequency range (0.1 to 10 Hz) as the SD. The computed long hydrodynamic wave's amplitude, caused by the SD, is not more then 20 cm. Therefore the waves transferring seismic energy can be discovered far from the coast by low-frequency EM observations.

海底地下地质结构的地震激发的电磁信号
建立了具有任意二维底部地质构造的边缘海盆地中地震电磁信号产生和传播的数学模型,包括地震电磁能量从岩石圈到水圈的传递以及电磁发射到大气的过程。模型盆地为日本海盆地中部二维方案,第一个磁信号产生于导电(0.02 S/m)的上地幔m层,假定t = 0时刻出现弱地震位移(SD)。SD的振幅和持续时间为几厘米和几秒,在不同的模拟中有所不同。来自M的初级信号在t = 3.5秒时到达海底,振幅约为50 pT。磁扩散到导电海水中的速度太慢,因此大气中的电磁信号是由于位于地震P波(来自M)与海底初始接触区域上方的垂直运动水柱Qs中的地磁场感应而产生的。由于海-气界面的地震-水动力场结构和电磁场共轭条件,地震-水动力磁场的水平分量B2首先在海面Qs顶部以下的薄水层中产生,而垂直分量B1在Qs中无处不在。磁信号传播后,在t = 10秒时,海面和10 km高度的B1分别高达250和150 pT。磁信号与SD具有相同的低频振荡范围(0.1 ~ 10 Hz)。计算得到的由SD引起的长水动力波幅值不超过20 cm。因此,低频电磁观测可以在远离海岸的地方发现传递地震能量的波。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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