HR: 1330h
AN: V22A-0561    [PDF]
TI: Subsidence of Askja Volcano, North Iceland: InSAR Observations and Different Modeling Approaches
AU: * Pagli, C
EM: carolina@hi.is
AF: Nordic Volcanological Institute, Grensasvegur 50, Reykjavik, 105 Iceland
AU: * Pagli, C
EM: carolina@hi.is
AF: Science Institute, University of Iceland, Dunhaga 3, Reykjavik, 107 Iceland
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Institute, Grensasvegur 50, Reykjavik, 105 Iceland
AU: Arnadąttir, T
EM: thora1@hi.is
AF: Nordic Volcanological Institute, Grensasvegur 50, Reykjavik, 105 Iceland
AU: Einarsson, P
EM: palli@raunvis.hi.is
AF: Science Institute, University of Iceland, Dunhaga 3, Reykjavik, 107 Iceland
AB: The Askja central volcano is located on the divergent plate boundary in North Iceland. The last major rifting episode happened in Askja in 1874-1876, but the most recent eruption in Askja occurred in 1961. Askja has been continuously deforming since crustal deformation measurements started in the area in 1966. GPS and optical leveling tilt measurements show subsidence of at least 75 cm from 1983 to 1998 at the volcano, without any eruptive activity. Interferometric analyses of Synthetic Aperture Radar images (InSAR), acquired by the ERS-1and ERS-2 satellites, have been conducted. The interferograms span the 1992-2000 period and cover a large area in central Iceland. A deformation signal around Askja, showing subsidence, is clearly evident in five different interferograms from two different Track/Frame pairs. The interferograms cover all of the Askja area and span different time periods. The observed deformation signal consists of a concentric fringe pattern, centered at the Askja caldera with a 20 km diameter, and slightly elongated in the north direction. The fringes are most closely spaced about 3 km from the center of deformation, suggesting that deformation gradients decrease near the center of Askja. Two approaches have been taken to model the InSAR data. Firstly, we assumed a Mogi model in an elastic half-space. A preliminary model indicates a 3 km source depth and a maximum vertical subsidence of 0.23 m, centered in the main caldera, from 1992 to 1998. An alternative approach is to use the finite element method in order to include topography. An axisymmetric model of a deflating spherical source has been constructed using the ANSYS software. Initially, a model that reproduces the Mogi source has been created, in order to compare analytical to finite element solutions. As agreement between the two sets of solutions was good, we have also constructed a model with a cone shape topographic relief, crudely approximating Askja. Results indicate that the maximum vertical displacement is not located above the center of the source, like in the half-space solutions, but on the sides of the volcano.
DE: 1206 Crustal movements--interplate (8155)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting