Crustal deformation of Miyakejima volcano, Japan since the eruption of 2000 using dense GPS campaign observation

Miyakejima is an active volcanic Island located about 175 km south of Tokyo, Japan. Miyakejima volcano erupted approximately every 20 years in the past 100 years. The latest eruptive activities since 2000 was different from those of the last 100 years, in that the activities included a caldera formation for the first time in 2500 years and gigantic volcanic gas emission that forced islander to evacuate over four and half years. In 2000, a dense GPS observation campaign had detected the magma intrusion in detail (e.g., Irwan et al., 2003; Murase et al., 2006). However, this campaign observation ceased from 2002 to 2010 because a large amount of volcanic gas prevented from entering to the island. Since 2011, we restarted the campaign observation by the dense GPS network, and examined the ongoing magma accumulation process beneath Miyakejima volcano to get insights about the future activity. In this analysis, we combined the data of our campaign observations, the data of the University Union in 2000, and the GEONET data. The observation data were analyzed by RTK-LIB (Takasu et al., 2007) using GPS precise ephemeris from IGS. We estimated the locations and volumes of the pressure sources beneth Miyakejima using an elevation-modified Mogi model (Fukui et al., 2003) and open crack model (Okada, 1992) during the two periods (2000 ~ 2012 and 2011 ~ 2012). We used the software of Magnetic and Geodetic data Computer Analysis Program for Volcano (MaGCAP-V) (Fukui et al., 2010), and estimated the source parameters by trial and error. During 2000 and 2012, a contracting spherical source and contracting dyke were estimated beneath the caldera and at the southwestern part of the island, respectively. In contrast, during 2011 and 2012, an spherical inflation source was estimated a few km beneath the caldera. This result suggest that Miyakejima is now storing new magma for the next eruption. Geospatial Information Authority of Japan (GSI) (2011) suggested that the inflation started since 2006. We will also carry out the GPS observation this autmn, and will present the result during 2012-2013.