报告题目：Progress in electromagnetic (EM) exploration of the oceanic mantle
（Part two: The cause of seafloor flattening）
报告人：Prof. Hisashi UTADA
Earthquake Research Institute (ERI), University of Tokyo, Japan.
Prof. UTADA has 43-years experience working in geo-electromagnetism, including electrical conductivity distribution, observation of the geomagnetic and geo-electric field, and dynamics in the core and the core-mantle interaction. Prof. UTADA’s work has been published in more than 160 academic papers on SCI journals including Science, EPSL, GRL, GJI, JGR, G-Cubed and Tectonophysics.
Plate tectonics is well accepted and we can find its conceptual picture even in high school textbooks. In many cases, the oceanic lithosphere is drawn like a plate of constant thickness except near the mid-oceanic ridges. This is neither an exaggeration nor a simplification but reflecting reality known as seafloor flattening. The feature of seafloor flattening is a consequence of thermal evolution of the LAS as a function of seafloor age. The typical feature of flattening can be simply explained by a model of cooling plate with artificially given constant thickness, but other models are also possible. Moreover, its physical cause is still controversial because this problem has been argued mostly on the basis of near-surface data such as seafloor depth or heat flow. The recent progress in geophysical imaging has enabled us to tackle this problem on the basis of deep mantle structure, which is supposed to be mainly controlled by the temperature distribution. Here I will present an example of investigating the problem of seafloor flattening by using EM exploration results recently obtained from the Pacific Ocean.