Three-dimensional electrical conductivity structure beneath North Pacific by using a submarine cable network

We present a model of 3-D electrical conductivity structure in the mid-mantle estimated by using voltage data by eight submarine cables as well as magnetic field data around the North Pacific. We assumed that 3-D heterogeneous conductivity distribution could be separated into radially symmetric (1-D) structure and 3-D perturbation. The 1-D model obtained by Utada et al. (2003) is employed as the reference model, and the distribution of the 3-D perturbation is inversely estimated so that the observation-calculation misfit is minimized. As the results, following features in the obtained 3-D conductivity structure are found to be similar to the seismic velocity structure: 1) conductive zone in the transition zone beneath Hawaii with a conductivity perturbation of factor of three; and 2) resistive zone in the uppermost lower mantle beneath Philippines with twice as resistive as the 1-D reference model. Assuming that the heterogeneities purely of thermal origin, temperature anomalies are estimated to be 200-300 degrees.