Long-period (30 days-1 year) electromagnetic sounding and the electrical conductivity of the lower mantle beneath Europe
Long-period (30 days-1 year) electromagnetic sounding and the electrical conductivity of the lower mantle beneath Europe
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DOI：
10.1046/j.1365-246x.1999.00854.x
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发表时间：
1999-07
影响因子：
2.8
通讯作者：
N. Olsen
中科院分区：
文献类型：
--
作者：
N. Olsen
c响应将电磁变化的垂直分量和水平分量的水平梯度连接起来，是推导地球电导率-深度剖面的基础。42个观测站的日平均值的时间序列通常具有50年的数据，用于估计1个月至1年期间的c -响应。采用Z: Y方法，这意味着垂直分量是局部的，而水平分量是通过一系列球面谐波的扩展来全球使用的。结合以往的分析结果，该方法对欧洲观测站的整个周期（从几小时到1年）得出了一致的结果，对应于300至1800公里的穿透深度。根据这些结果得出的1- d电导率模型显示，在z=800公里处，电导率随深度z增加到约2 S m-1，而在z=800至2000公里之间，电导率几乎不变，值为3-10 S m-1。与地幔物质的实验室测量结果非常吻合。在2000公里以下，电导率很难分辨。然而，最佳拟合模型表明电导率进一步增加至50至150 S m-1之间。
The C-response connects the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations and forms the basis for deriving the conductivity–depth profile of the Earth. Time-series of daily mean values at 42 observatories typically with 50 years of data are used to estimate C-responses for periods between 1 month and 1 yr. The Z: Y method is applied, which means that the vertical component is taken locally whereas the horizontal components are used globally by expansion in a series of spherical harmonics. In combination with results from previous analyses, the method yields consistent results for European observatories in the entire period range from a few hours to 1 yr, corresponding to penetration depths between 300 and 1800 km. 1-D conductivity models derived from these results show an increase in conductivity with depth z to about 2 S m-1 at z=800 km, and almost constant conductivity between z=800 and z=2000 km with values of 3–10 S m-1, in good agreement with laboratory measurements of mantle material. Below 2000 km the conductivity is poorly resolved. However, the best-fitting models indicate a further increase in conductivity to values between 50 and 150 S m-1.