Electromagnetic Study of the Stagnant Slab

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This project aimed to study electrical signature of the stagnant slab whose presence was well established by seismic tomography, and was carried out in the Northeaster district of China and the Primorski region of Russia for three years from 2003 to 2005 fiscal year.In Jilin and Liaoning provinces of the NE part of China, observations of electric field variations were made by using telephone lines collaborating with Professor G.Z.Zhao of Institute of Geology, China Earthquake Administration. We successfully obtained high-quality electric field data from 3 lines in Jilin and 4 lines in Liaoning provinces. Three components of geomagnetic field variations were also recorded at Changchun magnetic observatory where an Ocean Hemisphere Magnetometer System has been operating since 1998. We also investigated past results of magnetotelluric surveys done by Chinese, and made a map of near-surface conductance in the study area which is useful for correcting galvanic effects on long period inducti … More on responses by land-ocean distribution or near-surface conductivity structure.In the Primorski district of Far-east Russia, we collaborated with Professor V.A.Nikiforov and his group. Though we spent much time to get permissions from federal authorities more than expected, we finally obtained a record of geo-electric variations, by using two pairs of electrodes that were installed about 30km apart from each other. Local telephone lines were used to connect these electrodes that enabled us to make measurements nearly in N-S and E-W directions. We also obtained some magnetotelluric results that had been done by Russian side.We carefully analyzed data thus obtained, and studied the one-dimensional distribution and lateral variation of the electrical conductivity in the mantle beneath the study are down to the transition zone. Combining results from this conductivity study, P-wave tomography, and high pressure experiments, we estimated the distribution of water in the mantle of this region. Results obtained in the present study were published in international journals as listed below. Less