HR: 0830h
AN: G21B-0268    [PDF]
TI: Spatio-Temporal Variations of Post-Seismic Deformation after the June 2000 Earthquake Sequence in SW Iceland
AU: * Arnadottir, T
EM: thora1@hi.is
AF: Nordic Volcanological Institute, Grensasvegur 50, Reykjavik, 108 Iceland
AU: Pollitz, F
EM: fpollitz@swave.wr.usgs.gov
AF: US Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Jonsson, S
EM: sj@eps.harvard.edu
AF: Harvard University, Dep. of Earth and Planetary Sci., Cambridge, MA 02138 United States
AU: Feigl, K L
EM: Kurt.Feigl@cnes.fr
AF: CNRS UMR 5562, 14 ave E. Belin, Toulouse, 31400 France
AU: Sturkell, E
EM: erik@vedur.is
AF: Icelandic Meteorological Office, Bustadavegur 9, Reykjavik, 150 Iceland
AU: Geirsson, H
EM: dori@vedur.is
AF: Icelandic Meteorological Office, Bustadavegur 9, Reykjavik, 150 Iceland
AU: Einarsson, P
EM: palli@raunvis.hi.is
AF: Science Institute, University of Iceland, Reykjavik, 107 Iceland
AB: We observe post-seismic deformation over at least two spatio-temporal scales after two Mw6.5 earthquakes that occurred in the South Iceland seismic zone (SISZ) in June 2000. At the first scale, we see a rapidly decaying deformation transient lasting no more than 2 months within 5 km of the two main shock ruptures. This local, month-scale transient is captured by several radar interferograms (InSAR) and is also observed at a few campaign GPS sites located near main shock faults. The second scale takes place over a characteristic time of the order of a year and is only detected by GPS measurements. Combining GPS observations from campaigns and continuous stations operated by the IMO (two of which were installed after June 2000), we observe significant changes of the velocity field out to a distance of about 20 km surrounding the main shock faults. This perturbation of the velocity field is most profound during 2000-2001, but decreases significantly during 2001-2002. Two different mechanisms are needed to explain the observed post-seismic deformation. The month-scale deformation pattern has been explained by poro-elastic rebound due to pore-fluid flow in response to the main shock induced pore-pressure changes [Jonsson et al., Nature, 2003]. In contrast, the year-scale deformation seems to be caused by visco-elastic relaxation of the lower crust and upper mantle in response to the coseismic stress changes. To simulate the year-scale deformation, we use a spherically stratified earth model with relaxing layers represented by visco-elastic lower crust and upper mantle, underlying an elastic upper crust. Preliminary modeling results suggest that the viscosity of the lower crust and upper mantle must be of the order $\sim 10^{18}$ Pa s to fit the observations. This value is near the lower bounds of previous estimates of sub- and lower-crustal viscosities, from post-glacial rebound and post-rifting relaxation in Iceland.
DE: 1206 Crustal movements--interplate (8155)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1242 Seismic deformations (7205)
DE: 8164 Stresses--crust and lithosphere
SC: Geodesy [G]
MN: 2003 Fall Meeting