12:00 PM - 12:15 PM
[SEM19-12] Fluid distribution beneath central and southern Kyushu imaged by 3-D electrical resistivity model
Keywords:3-D electrical resistivity model, Fluid distribution, magmatism, seismic activity, mantle wedge
The Philippine Sea Plate, whose subduction involves the formation of the volcanic island of Kyushu, in and around Kyushu is classified into three portions: a younger portion, an older portion, and the other part of the Kyushu–Palau Ridge between the two portions. A non-volcanic region distributes in central Kyushu above a junction where the three portions of the subducting Philippine Sea Plate contact with each other. Owing to the subduction of the Philippine Sea Plate, moment magnitude 7-class thrust earthquakes have repeatedly occurred in the Hyuga-nada, lying offshore of the southeast Kyushu. In addition, recent studies using continuous global-navigation-satellite-system data have revealed that long-term slow slip events and short-term slow slip events occur in the Hyuga-nada. Besides, most of the earthquakes in the land area occur along three tectonic lines: Oita-Kumamoto tectonic line, Usuki-Yatsushiro tectonic line and Butsuzo tectonic line.
Fluid distribution in the mantle wedge is an essential factor for the seismic activity and magmatism leading to volcanic activity. Electromagnetic sounding data have high sensitivity to a few percent of interconnected fluids (aqueous fluid and melt). In this study, we generated a three-dimensional (3-D) electrical resistivity model by inverting magnetotelluric data, which covers the active southern volcanic region and the non-volcanic region, to examine the fluid distribution in the mantle wedge beneath Kyushu. We find three important conductive features in the 3-D model. A magma system and a fluid system imaged as two vertical conductors relating to slab-derived fluid, which exist along the volcanic front beneath the southern volcanic region and the non-volcanic region, respectively. The other conductor, relating to the presence of slab-derived fluid and serpentinite in the mantle wedge, appears at a blank area of the slow slip events.