全球地壳、上地幔电导率经向分布特征

LONGITUDINAL DISTRIBUTION CHARACTERISTICS OF THE CONDUCTIVITY WITHIN THE EARTH'S CRUST AND UPPER MANTLE

计算了对应于各个ＵＴ小时的２４个经度带的Ｓｑ地下感应场对外部施感场的响应函数，应用Ｓｃｈｍｕｃｋｅｒ＇ｓＡｐｐｒｏｘｉｍａｔｅＥｕｒｉｓｔｉｃ反演方法，计算了这些经度带的地下等效层及其电导率分布，得到了地壳－上地幔电导率经向分布的大致图案。对该结果的分析研究得出，全球电导率经向分布存在着极大的不均匀性，在０－４００ｋｍ深度范围内，太平洋和大西洋为低导区；欧亚大陆与美洲大陆为高导区。电导率分布特征与岩石层结构有明显的相关性：在俯冲带，低导区由海洋向大陆下插入；在大洋中脊表现为高导电性。反演结果与地震层析成像结果的比较表明，地下高电导区和低电导区的位置分别对应于地震波低速区和高速区。

On the basis of our previous sutdy on the longitudinal variation of the Sq-field, the response function is calculated for different longituinal regions corresponding to each UT hour. By means of Schmucker's Approximate Euristic Method, longitudinal distribution of the conductivity in the Earth's crust and upper-mantle is obtained. It shows a great longitudinal inhomogeneity of conductivity: relatively high conductivity in European-Asian and American regions and low in Pacific and Atlantic regions in the depth of 0-400km. The low conductivity layer in the upper mantle of Pacific region extends under the Asian mantle, while at mid-ocean ridges there are high conductivity layers, which agree with the idea of the plate-tectonic theory. The conductivity distribution is compared with the Earth's velocity structure from the global seismic tomography technique. A good correspondance between low (or high) conductivity with high (or low) velocity is obtained.