HR: 11:35h
AN: G12A-06 INVITED     [Abstracts]
TI: Post-Seismic Deformation Following the June 2000 Earthquake Sequence in Southwest Iceland
AU: * Arnadottir, T
EM: thora1@hi.is
AF: Nordic Volcanol. Cent., Univ. of Iceland, Reykjavik, IS-107 Iceland
AU: Jonsson, S
EM: sj@erdw.ethz.ch
AF: USGS, 345 Middlefield Rd, Menlo Park, 94025 United States
AU: Pollitz, F
EM: fpollitz@usgs.gov fpollitz@usgs.gov fpollitz@usgs.gov
AF: Inst. of Geophys. ETH, Hoenggerberg, Zurich, CH-8093 Switzerland
AU: Jiang, W
EM: weiping@hi.is weiping@hi.is
AF: Nordic Volcanol. Cent., Univ. of Iceland, Reykjavik, IS-107 Iceland
AU: Feigl, K L
EM: Kurt.Feigl@cnes.fr
AF: CNRS, 14 ave. E. Belin, Toulouse, 31400 France
AU: Sturkell, E
EM: erik@vedur.is
AF: Icel. Meteol. Off., Bustadavegur 9, Reykjavik, IS-150 Iceland
AU: Geirsson, H
EM: dori@vedur.is
AF: Icel. Meteol. Off., Bustadavegur 9, Reykjavik, IS-150 Iceland
AB: Two Mw6.5 earthquakes occurred in the South Iceland seismic zone (SISZ) in June 2000, the first one triggering at least three Mw$>$5 events on Reykjanes Peninsula. Modeling of co-seismic deformation, and aftershock locations indicate the two main shocks ruptured N-S, right-lateral strike slip faults, spaced about 17 km apart. We use campaign GPS observations from 1992-2000 to estimate the steady state plate motion in the area, and subtract from the station displacements during 2000-2004 to obtain the post -seismic deformation field. We observe significant changes in the velocity field in the SISZ, as well as on Reykjanes Peninsula due to the June 2000 earthquake sequence. The perturbation of the velocity field is most profound during the first year (2000-2001) in the main shock epicentral area. In the SISZ we observe post-seismic deformation over two spatio-temporal scales. On the first scale, we see a rapidly decaying deformation transient within 5 km of the two main shock ruptures, lasting no more than 2 months. This local month-scale transient is captured by several radar interferograms (InSAR) and is also observed at a few campaign GPS sites located near the main shock faults. The deformation pattern has been explained by poro-elastic rebound due to pore-fluid flow in response to the main shock induced pore-pressure changes [JĒnsson et al., Nature, 2003]. The second scale has a characteristic time of the order of a year and is detected by GPS measurements alone. Different models are tested to explain the year-scale deformation. Models of visco-elastic relaxation of the lower crust and upper mantle in response to the coseismic stress changes suggest that the viscosity of the lower crust and upper mantle must be of the order 10$^{18}$ Pa s to fit the observations. Simple models of afterslip to fit the post-seismic deformation data are also tested. We use these models to calculate changes in Coulomb failure stress in the main shock epicentral area from 2000-2004.
DE: 7260 Theory and modeling
DE: 8158 Plate motions--present and recent (3040)
DE: 7218 Lithosphere and upper mantle
DE: 1208 Crustal movements--intraplate (8110)
DE: 1242 Seismic deformations (7205)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting