HR: 0800h
AN: T21C-0493    [Abstracts]
TI: Seismic Attenuation in the Vrancea Zone and Surroundings: Delamination or Subduction?
AU: * Dardac, M
EM: mirela_dardac@yahoo.com
AF: Dept. of Geophysics University of Bucharest, 6 Traian Vuia St, Bucharest, 020956 Romania
AU: Russo, R M
EM: russo@geology.ufl.edu
AF: Dept. of Geological Sciences University of Florida, 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Mocanu, V
EM: mocanu@gg.unibuc.ro
AF: Dept. of Geophysics University of Bucharest, 6 Traian Vuia St, Bucharest, 020956 Romania
AU: Popa, M
EM: mihaela@infp.ro
AF: Nat. Inst. of Eearth Physics, PO Box MG-2, Bucharest, 077125 Romania
AU: Radulian, M
EM: mircea@infp.ro
AF: Nat. Inst. of Eearth Physics, PO Box MG-2, Bucharest, 077125 Romania
AU: Bonjer, K
EM: Klaus.Bonjer@gpi.uni-karlsruhe.de
AF: Inst. of Geophysics University of Karlsruhe, Hertzstrasse 16, Karlsruhe, 76187 Germany
AB: We present results of seismic attenuation measurements focused on the Vrancea bend zone of the Carpathians, in order to delimit the lithosphere and asthenosphere in this area. Attenuation observed at 27 stations of the German-Romanian K2 seismic network allows us to evaluate models of subduction or delamination proposed for this region. The seismic stations are homogeneously distributed above concentrated intermediate depth Vrancea seismicity, which occurs beneath the contact between the Moldavian East European Platform, the Scythian Platform, and the Moesian Platform, to the east and southeast, and terranes of the Transylvania Basin lying within the Carpathian arc. The delamination model implies strong upwelling and horizontal inflow of asthenosphere into the gap between the delaminating and remnant lithosphere. The other model implies downwelling and perhaps lateral-horizontal inflow along the slab detachment or tear. The models imply different distributions of density and rheological properties associated with the different lithosphere - asthenosphere structures. We use the ratio of spectral amplitudes of P and S waves from vertical and transverse seismograms to estimate the S to P ratio in the frequency domain, and then we calculate Qs, the relative shear wave attenuation via two complementary techniques: For 400 combinations of iteratively increasing-length windows of P and S, we estimate individual and composite Qs. This allows us to calculate uncertainties in Qs. We find that stations located near and above the Vrancea zone and in the Transylvanian Basin, attenuation is high (low Q). Stations situated on the East European, Moesian, and Scythian Platforms are characterized by higher Qs (low attenuation). We interpret the high attenuation in the Vrancea and Transylvanian Basin is the result of shallow hot asthenosphere present in this area.
DE: 7205 Continental crust (1219)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: Fall Meeting 2005