Slab segmentation controls the interplate slip motion in the SW Hellenic subduction and drives Aegean deformation and seismicity
IPGP - Îlot Cuvier
Séminaires de Sismologie
Observatoire National d'Athènes
We study the Western Hellenic subduction zone for over 25 years in the frame of European and bilateral collaborations by using integrated approach of its seismic structure and activity. This presentation will focus on the recent results on the imaging of the Hellenic slab top acquired by teleseismic receiver function analysis on a dense 2-D seismic land array. We resolve the slab topography of the most recently subducted part of the Ionian Sea of the African plate down to 100 km depth. It appears segmented from the Gulf of Corinth to south of Kythira island, over 300km distance, into dipping panels 30–50 km wide by a series of nine along-dip faults. We have resolved intermediate-depth M>6 earthquakes to be located on those faults, which implies that they are seismically active at 70 km depth. We have also constrained the smaller magnitude earthquakes of the slab uppermost part commonly related to dehydration processes to be clustered along these faults. Our new observations suggest that the general slab rollback occurs here in a differential piecewise manner imposing its specific stress and deformation onto the overriding Aegean plate. Further RF offshore imaging on 4 OBS sites allows to resolve the depth and geometry of the thrust interplate boundary. Our data support a trenchward continuation of the slab faults and correlation with the similarly segmented thrusting contact of the Mediterranean Ridge accretionary wedge over the upper plate. The slab faults may control location and size of major historical and instrumental megathrust earthquakes. We study the Mw 6.8 14.02.2008 interplate earthquake offshore SW Peloponnesus and show that its nucleation, and aftershocks sequence are confined to one slab panel between two adjacent along-dip faults. Its rupture pattern appears controlled by not only the offshore slab top segmentation but also the upper plate sea-bottom morphology.