HR: 14:40h
AN: G13C-05    [Abstracts]
TI: Twenty Years of GPS in Iceland: What Have we Learned About the Plate Boundary?
AU: * Arnadottir, T
EM: thora1@hi.is
AF: Nordic Volcanological Center, Inst. of Earth Sciences, Sturlugata 7, Reykjavik, IS-101, Iceland
AU: Lund, B
EM: Bjorn.Lund@geo.uu.se
AF: Dep. of Earth Sciences, Uppsala University, Villavagen 16, Uppsala, SE-75236, Sweden
AU: Jiang, W
EM: wpjiang@whu.edu.cn
AF: GPS Research Center, Wuhan University, Wuhan, 430079, China
AU: Geirsson, H
EM: dori@vedur.is
AF: Icelandic Meteorological Office, Bustadavegur 9, Reykjavik, IS-101, Iceland
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Center, Inst. of Earth Sciences, Sturlugata 7, Reykjavik, IS-101, Iceland
AU: Einarsson, P
EM: palli@raunvis.hi.is
AF: Inst. of Earth Sciences, University of Iceland, Reykjavik, IS-101, Iceland
AB: Iceland is located on the Mid-Atlantic Ridge, straddling the boundary between the North American and Eurasian plates. It is therefore one of the few places on Earth where direct observations of extensional processes related to plate spreading are possible. Since the first GPS experiment in 1986, most GPS campaigns have focused on limited parts of the plate boundary or individual volcanoes. Results from two nationwide GPS campaigns provide the first 3D velocity and deformation rate maps of the whole country during 1993--2004. The horizontal deformation appears to be accommodated by extension in a ~100 km wide region in North Iceland, whereas the zone of deformation in southern Iceland appears to be wider due to the overlapping western and eastern volcanic zones. The existence of a micro plate (the Hreppar block) has been suggested in the area between the two overlapping rift zones in southern Iceland. However, this has been difficult to confirm as the area is only about 100 km wide. In general, the observed relative horizontal motion agrees remarkably well with predictions from plate motion models, such as NUVEL-1A and REVEL. The horizontal velocities from 1993--2004 across the northern volcanic zone show that the velocity increase observed by GPS during 1987--1992, interpreted as a post-rifting signal following the 1975--1984 Krafla rifting episode, is no longer present. A significant rate of vertical uplift is observed in central Iceland during 1993--2004, with a maximum of the same order of magnitude as the rate of spreading (~20 mm/yr). The broad pattern of uplift can be explained by glacio-isostatic adjustment due to the thinning of Vatnajökull and three other large ice caps in Iceland since 1890. The residual vertical velocities indicate consistent areas of uplift or subsidence, mostly centered along the plate boundary. These observations and many of the previous GPS studies indicate that the elastic part of the lithosphere in Iceland is ~10 km thick, and lower crust/upper mantle viscosities are low (1-10 × 10¹⁸ Pa s). This suggests that transient deformation due to earthquakes and rifting events are a short lived phenomena (a decade) compared to the time interval between these events (hundred years). Presently, a significant portion of the strain built up by plate motion across the transform zone in south Iceland does not appear to be released seismically. It is not clear how the aseismic deformation in this region is accommodated in the upper crust.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Geodesy [G]
MN: 2007 Fall Meeting