HR: 09:00h
AN: T51E-05    [Abstracts]
TI: Variation of Seismic Coupling Along the Western Hellenic Subduction with slab detachment and upper plate structure
AU: * Laigle, M
EM: laigle@ipgp.jussieu.fr
AF: Sismologie Exp‚rimentale, Institut de Physique du Globe de Paris, case 89, 4 Place Jussieu, Paris cedex 05, 75252 France
AU: Sachpazi, M
EM: m.sachp@egelados.gein.noa.gr
AF: Geodynamics Laboratory, National Observatory of Athens, Lofos Nymfon, Athens, 00000 Greece
AU: Hirn, A
EM: hirn@ipgp.jussieu.fr
AF: Sismologie Exp‚rimentale, Institut de Physique du Globe de Paris, case 89, 4 Place Jussieu, Paris cedex 05, 75252 France
AB: The highest seismic activity in Europe occurs currently in the region of the Western Hellenic Arc. However, it has been commonly considered as a largely aseismic subduction zone, from the comparison of a small rate of shortening derived from the seismic moment release, with a large rate of convergence inferred from geology. In the northern part, in the Ionian Islands, we have recently showed instead that full seismic coupling could be achieved accordingly to the model of control by plate tectonics forces, with a trenchward motion of the upper plate, and the pull of the broken-off slab that is here missing in the balance. We suggested that the moderate moment rate can be related to a shallow downdip limit that is documented for the seismogenic part of the subduction interplate using seismic reflection profiling and local earthquakes tomography,in agreement with the shallow depth (10-15 km) of the major historical subduction earthquakes. This peculiarity may be attributed to the ductility of the lower crust of the upper plate resulting from orogenic thickening, which also allows a d‚collement of the upper crust and its overriding of the lower plate. This new view on the seismic coupling of this region leads us to extend the discussion to the part further South, from West of Peloponnesus to Western Crete, where major Mediterranean earthquake occured in the past. There, we suggest that despite a similar seismic moment release rate and trenchward upper plate velocity, seismic coupling might be incomplete on the subduction interplate that would have there a wider seismogenic part. This interpretation is based on analyses of the structural conditions, plate tectonics forces as well as spatial- and magnitude-distributions of interplate seismicity, that strongly change along the Hellenic Arc. A cause may be the lateral addition of extra weight to the slab pull force in this area, due to free-fall of the slab part that has broken off from the surface farther north, and that seems to have remained attached to the slab part beneath Crete. This increased slab pull would reduce the compressive normal stress across the seismogenic part of the subduction interplate and thus causes partial seismic coupling in its shallower part, that may however participate to the megathrust earthquake rupture. Hints at anomalies in structure and seismicity, which need to be resolved, may relate to the present location of the edge of the tear in the slab.
DE: 7230 Seismicity and seismotectonics
DE: 7215 Earthquake parameters
DE: 7218 Lithosphere and upper mantle
DE: 3025 Marine seismics (0935)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting