HR: 0800h
AN: T21B-0468    [Abstracts]
TI: Stress Variations Before and During the two M=6.5 Earthquakes of June 2000 in the South Iceland Seismic Zone.
AU: * Lund, B
EM: bjorn.lund@geo.uu.se
AF: Uppsala University, Dep. of Earth Sciences, Villavägen 16, Uppsala, 752 36 Sweden
AU: Lindman, M
T21B-0468 AF: Uppsala University, Dep. of Earth Sciences, Villavägen 16, Uppsala, 752 36 Sweden
AU: Arvidsson, M
T21B-0468 AF: Uppsala University, Dep. of Earth Sciences, Villavägen 16, Uppsala, 752 36 Sweden
AU: Slunga, R
T21B-0468 AF: Uppsala University, Dep. of Earth Sciences, Villavägen 16, Uppsala, 752 36 Sweden
AU: Bödvarsson, R
T21B-0468 AF: Uppsala University, Dep. of Earth Sciences, Villavägen 16, Uppsala, 752 36 Sweden
AB: In June 2000, the South Iceland Seismic Zone (SISZ) was struck by two M=6.5 strike-slip earthquakes, only four days and 17 km apart. During the fifteen years of operation of the SIL seismic network, 1990 to present, more than 200,000 earthquakes down to magnitude zero have been recorded in the area. In this study, we use the focal mechanisms in the SIL database to do a detailed investigation, in time and space, of the stress field in the SISZ before and after the large earthquake sequence. Large scale inversions show that the regional maximum horizontal stress, S_H, is rather well constrained in the direction N 50° E. Zooming in on the epicentral regions of the two earthquakes, still using large amounts of data, we observe variations with time. In the June 17 event area, S_H rotates slightly east-westward, whereas in the June 21 event area S_H rotates significantly toward north-south. We increase the resolution further, both in area and in depth, by taking full advantage of the features of the SIL analysis system such as spectral amplitude derived focal mechanisms and correlation based relative relocations. Highlights of the investigations are a clear variation in S_H directions with depth in the June 17 area in the years before the M 6.5 event, and a pronounced jump in S_H directions, going from north to south along the fault, in the June 21 area after the event. We model the stress anomaly before the June 17 event as a pore fluid driven phenomenon and infer the depth in the crust where this fluid effect becomes important. The June 21 area stress variation is studied using various models of earthquake interaction, including poroelastic models.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8123 Dynamics: seismotectonics
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: Fall Meeting 2005