[SCG63-15] Fluid distribution beneath volcanically and seismically active island, Kyushu, based on 3-D electrical resistivity model
Keywords:3-D electrical resistivity models, Fluid distribution, Volcanically and seismically active island, Mantle wedge, Slow slip events
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. The 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 (Mw) 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, in the land area, historic earthquakes of at least Mw 6.0 repeatedly occur along the three tectonic lines, which travels across the central part of Kyushu almost in an E-W direction.
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 presentation, three-dimensional (3-D) electrical resistivity models by inverting magnetotelluric (MT) data and/or network-MT data, which have been acquired on the whole of Kyushu island by various surveys, are shown to discuss the fluid distribution beneath Kyushu. The 3-D resistivity models indicate magma systems and fluid systems relating to slab-derived fluid as significant conductive features/anomalies. In addition, the conductive anomalies exist along the volcanic front beneath the northern and southern volcanic regions, respectively. Importantly, a clear conductive anomaly in the 3-D models fail to reach the crust through the Moho discontinuity beneath the non-volcanic region in Kyushu. Moreover, another conductor, relating to the presence of slab-derived fluid in the mantle wedge, appears at a blank area of the slow slip events.