HR: 0830h
AN: V51J-0414    [PDF]
TI: Crustal Deformation of Iwojima Volcano Detected by SAR Interferometry and GPS Observations
AU: * Yarai, H
EM: yarai@gsi.go.jp
AF: Geographical Survey Institute, Kitasato-1, Tsukuba, 305-0811 Japan
AU: Murakami, M
EM: mccopy@gsi.go.jp
AF: Geographical Survey Institute, Kitasato-1, Tsukuba, 305-0811 Japan
AU: Ozawa, T
EM: taku@gsi.go.jp
AF: Japan Society for the Promotion of Science/ Geographical Survey Institute, Kitasato-1, Tsukuba, 305-0811 Japan
AU: Tobita, M
EM: tobita@gsi.go.jp
AF: Geographical Survey Institute, Kitasato-1, Tsukuba, 305-0811 Japan
AU: Fujiwara, S
EM: fujiwara@gsi.go.jp
AF: Geographical Survey Institute, Kitasato-1, Tsukuba, 305-0811 Japan
AU: Miyamoto, J
EM: dora@gsi.go.jp
AF: Geographical Survey Institute, Kitasato-1, Tsukuba, 305-0811 Japan
AB: Iwojima volcano is located in the Izu-Bonin islands arc, about 1250 km south of Tokyo. Small phreatic eruptions occurred more than 15 times in Iwojima volcano since 1889. Crustal deformation has occurred on a remarkable scale at the volcano. We tried to comprehend the deformation field of Iwojima volcano by SAR interferometry and campaign GPS observation. We processed 20 different pairs of JERS-1 SAR data spanning 1992 to 1998. The concentric circular fringes around Motoyama, northeastern Iwojima Island, can be seen at most interferograms. The line of sight (LOS) displacement at the center of Motoyama was increasing constantly. In Chidoriga-hara, the southwestern Iwojima Island, the fringes patterns of the interferograms were not constant but changed episodically. We have started the GPS campaign observation since August 2002. The observation stations have been observed at 3 months interval. The shrinking of Motoyama and the inflation of Chidoriga-hara were detected by GPS observations. The largest horizontal displacement of above 7cm was observed near the Chidoriga-hara during August and November 2002. The stations around Motoyama have displaced constantly. In contrast, the speed of displacements around Chidoriga-hara is not constant but decreasing with time. These features of deformation appeared by GPS campaign observations is similar to interferograms from JERS-1 InSAR. We constructed a preliminary model for the deformation field of Iwojima. The deformation field can be explained by two sources, a deflation source beneath the center of Motoyama and a tensile fault beneath Chidoriga-hara. The location and the volume change rate of the deflation source estimated from GPS observations (-0.7\times\(10^7\)m\(^3\)/year, 3.0km depth) is near the deflation source which are estimated from JERS-1 InSAR (-0.4-1.5\times\(10^7\)m\(^3\)/year, 1.5-3.0km depth).
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
DE: 8419 Eruption monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting