[U-02_28AM1] Particle Geophysics

★ [U02-01] Muographic observations in Satsuma Iwojima, Japan

*Hiroyuki TANAKA¹ (1.Earthquake Research Institute, The University of Tokyo)

Keywords:Muography, Muon, Volcanic Conduit, Imaging

Satsuma-Iwojima volcano continuously discharges large amounts of volcanic gasses without significant magma discharge. One of the proposed mechanisms of this continuous gas discharge is conduit magma convection. In this hypothesis, a magma conduit is connected to a deep magma chamber and a "degassing" phenomenon drives convection. Once the volatile component is released (by degassing) at the top of the magma conduit, the degassed magma sinks through the non-degassed magma occupying the pathway. A continuous supply of non-degassed magma from the magma chamber ensures that there is compensation for the degassed magma and the cycle continues. In 2008, a muography detector was placed at the foot of Satsuma-Iwojima volcano, and it captured an image of a large, shallow depth, low-density region existing beneath the crater floor. Degassing magma, with its high proportion of bubbles, has been interpreted as being the low-density region, and its dimension (location and size) was compared to the results from other field measurements, laboratory and theoretical studies. In 2013, an improved muography detector was developed and placed at the same location as the 2008 observation to exploit advanced muographic images in Satsuma-Iwojima. The recent progress in muographic observations will be reported.