November 2008 - May 2010
Tetsuo is interested in the earth’s interior, especially the structure and dynamics of the crust and mantle. To investigate the crust and mantle he employs Magnetotellurics, which is an electromagnetic method providing resistivity (or conductivity, which is the inverse of resistivity) of the earth’s interior structure. The electrical resistivity of the crust and mantle is influenced by composition, temperature, degree of hydration, and the presence of interconnected conducting phases such as melt. By quantifying the electrical resistivity scientists have been able to address issues of crust and mantle dynamics such as water release into the mantle wedge in the subduction system and patterns of melt transport in the mid-ocean ridge system.
One of his current research targets is the Mariana subduction system in the western Pacific. Subduction is an inevitable consequence of plate tectonics in which seafloor spreading at mid-ocean ridges is accommodated by the return and recycling of oceanic lithosphere in the mantle. The interaction of the subducting slab with the surrounding mantle results in constructional volcanic processes in the form of island-arcs and, in some settings, can also be tied to back-arc spreading and the formation of new oceanic crust. The Mariana subduction system is one end-member of the worldwide subduction systems, where the old (140-150 Myear) Pacific Plate steeply subducts under the Philippine Sea plate and new seafloor forms at the back-arc spreading center of the Mariana Trough. The Marianas system is an obvious place to image the release of water from the subducting slab, the subsequent melting of the mantle, and the delivery of melt to the surface, as it has a well-developed frontal arc, active arc volcanoes, and a slow-spreading back-arc ridge.
In collaboration with WHOI scientists including Alan Chave and Rob Evans, his main work at WHOI is the analysis and interpretation of electromagnetic data in the Marianas system, which was acquired during collaborative research cruises between Japan, the United States and Australia in 2005-2007. The Marianas system is a target area of the Subduction Factory in the MARGINS-NSF program, and other studies in seismology and marine geophysics and geochemistry have been conducted actively. Their research results are synthesized with the results of these studies and additional studies of petrology and mineralogy of mantle rocks and minerals to advance our knowledge of the Mariana subduction system. Study of the back-arc spreading center in this work is also related to the InterRidge program of ridge-crest studies. He has also investigated improvements in the inversion process of data including the Mariana data; one is an application of additional electromagnetic response functions and another is data selection on the statistics basis. He will work on a marine electromagnetic experiment off the coast of Nicaragua in the eastern Pacific to study the distribution and amount of water input into the Costa Rica-Nicaragua subduction system.
Tetsuo received his Ph. D. in Earth and Planetary System Sciences from Kobe University, Japan, in 2008. His dissertation research is on the analysis and interpretation of marine magnetotelluric data and a methodology for correcting topographic distortions on marine magnetotelluric data. He has participated in several cruises of magnetotelluric surveys of the crust and mantle, marine geomagnetic and gravity surveys, and electromagnetic surveys using artificial sources for imaging the structure of hydrothermal vents and reservoirs of methane hydrates around Japan including the Marianas. He was a post-doctor at the National Institute of Polar Research, Japan, after receiving his Ph. D., pursing the analysis of electromagnetic data offshore Antarctica to image mantle electrical resistivity structure beneath the ocean-continental boundary related to the break-up of the Gondwana supercontinent.