[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM14-P12] Resistivity structure of the Pacific plate and the asthenosphere on the seaward slope of the Japan Trench, off Sanriku

*Miku Sakurai¹, Tada-nori Goto¹, Shinya Sato², Hiroshi Ichihara³, Takafumi Kasaya⁴, Makoto Yamano⁵ (1.University of Hyogo, 2.Kyoto Univesity, 3.Nagoya Univesity, 4.Japan Agency for Marine-Earth Science and Technology, 5.the Univesity of Tokyo)

Keywords:Japan Trench, resistivity structure, magnetotelluric, fluid distributions, asthenosphere

The occurrence of plate boundary earthquakes is related to the presence of water in the rock. The strength of the crust depends on the water content. Therefore, it is important to investigate the distribution and quantity of water at depth for understanding the occurrence of earthquakes.
Yamano and Kawada (2016) report that fluids exist inside the oceanic plate, and the thichness of permeable layers increase towards the trench. However, it is not yet clear on the source of the fluid.
In this study, seafloor electromagnetic field surveys were carried out on the Pacific Plate far off Sanriku, Japan, to estimate the resistivity structure for discuss the deep subsurface conditions and water distributions.
Ocean bottom electromagnetometers were installed on the seafloor to record the natural fluctuations of magnetic and electric field. The data were used to estimate the subsurface resistivity structure with the magnetotelluric method.
The results obtained by the two-dimensional inversion scheme revealed the existence of a low resistivity zone in the oceanic upper mantle depth (at the asthenosphere) before the subdution. The obtained feature was similar to the published researches below the Mariana subduction zone. In the future, we will estimate the resistivity structure inthe oceanic plate. It is necessary to elucidate where the fluid exists and comes from.