HR: 0800h
AN: T31A-1284    [Abstracts]
TI: Comparative analysis of topographic, structural and microseismicity images of the two active transform structures in northern Iceland
AU: Villemin, T
EM: thierry.villemin@univ-savoie.fr
AF: LGCA, Universite de Savoie Campus Scientifique, Le Bourget du Lac, 73376 France
AU: * Bettinelli, P
EM: pierre.bettinelli@cea.fr
AF: CEA, LDG, BP12, Bruyeres-Le-Chatel, 91680 France
AU: * Bettinelli, P
EM: pierre.bettinelli@cea.fr
AF: LGCA, Universite de Savoie Campus Scientifique, Le Bourget du Lac, 73376 France
AB: The Tj\"ornes Fracture Zone is a dextral transform zone connecting the off shore Kolbeinsey ridge to the on land rift zone in northern Iceland. The present day seismic image of this zone reveals two distinct NNW-SSE lineaments : the Husavik-Flatey Fault and the Grimsey lineament. several scarps and fault zones marks the trace of the Husavik-Flatey Fault whereas no topographic evidence correspond to the seismic clusters recorded along the Grimsey lineament. Both from a topographical point of view and microseismicity distribution, the Grimsey Lineament is similar to the South Iceland Seismic Zone. We analysed time and space distribution of the 1994-2003 seismicity. The maximum magnitude were 4,7 on both Grimsey lineament and Husavik-Flatey Fault. In addition to a permanent low level activity, we observed two typical different types of crisis : both correspond to a huge of events, the first one, not associated with significiant energy relaxation, contrary to the other one. During the 9 years studied, only one high energy crisis occured on the Husavik-Flatey Fault, whereas four events of that type happened on the Grimsey Lineament. Total energy relaxed is the same on both active structures. Seismic activity is restricted to the Western part of the Husavik-Flatey Fault whereas the Grimsey Lineament is active to all along his trace. For the Husavik-Flatey Fault, magnitude distribution agree with the Gutenberg-Richter law for all magnitude larger than 0,9. The b-value is 0,91. Magnitude distribution on the Grimsey Lineament doesn't correspond to a similar single law. We observed a Gutenberg-Richter law only for magnitude ranging 1 to 2,5, larger events indicating clearly a default of large earthquakes. Similar breaked distribution was observed on the South Iceland Seismic Zone before the large events of June 2000. This study suggest very clear difference in the functioning cycle of the two active transform zones in northern Iceland. This differences have to be taking into account for the seismic risk evaluation.
DE: 9325 Atlantic Ocean
DE: 7230 Seismicity and seismotectonics
DE: 8010 Fractures and faults
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting