HR: 1340h
AN: T53B-0503    [Abstracts]
TI: Constraints from Moho Geometry and Crustal Thickness on the Geodynamic Origin of the Vrancea Seismogenic Zone (Romania)
AU: * Mucuta, D M
EM: dmucuta@geol.sc.edu
AF: Department of Geological Sciences, University of South Carolina, 701 Sumter Street, Columbia, SC 29208 United States
AU: Knapp, C C
EM: camelia@geol.sc.edu
AF: Department of Geological Sciences, University of South Carolina, 701 Sumter Street, Columbia, SC 29208 United States
AU: Knapp, J H
EM: knapp@geol.sc.edu
AF: Department of Geological Sciences, University of South Carolina, 701 Sumter Street, Columbia, SC 29208 United States
AU: Popa, M
EM: mihaela@infp.ro
AF: National Institute of Earth Physics, PO Box MG-2, Bucharest, Magurele, 4930117 Romania
AB: Reprocessing of industry deep seismic reflection data (Ramnicu Sarat and Braila profiles) from the Eastern Carpathian foreland of Romania provides important new constraints on geodynamic models for origin of the intermediate depth Vrancea Seismogenic Zone (VSZ). Mantle (70-200 km) earthquakes of the VSZ are characterized by high magnitudes (greater than 6.5), frequent occurrence rates (approximately 25 years), and confinement in a very narrow (30 by 70 by 200 km) near vertical body atypical for a Wadati-Benioff plane. Crustal seismicity of magnitudes less than 6 occurs over a much broader region (150 by 200 by 45 km) in the Southeastern Carpathian foreland and is both vertically (25 km) and horizontally (50-100 km) offset to the E from mantle seismicity. The foreland basin in front of the 110 degrees bend of the Southeastern Carpathians is characterized by (1) an 18 km thick Miocene-Quaternary sedimentary cover (2) late Pleistocene-Quaternary extensional faults, and (3) unusually low topography. Two deep (20 s) seismic reflection profiles (64 km total length) from the SE Carpathian foreland reveal (1) a high-amplitude, gently east-dipping reflection across most of the section from what we interpret to be the Moho at 15 s (45 km), (2) a thick sedimentary cover increasing in thickness from east (4 s; 8 km) to west (7 s; 14 km), (3) an eastward increase in crustal thickness from 38 km (above the VSZ) to 42 km, and (4) seismic and topographic evidence for a newly imaged, possibly seismically active basement fault with a surface offset of 30 m. Along with the relocation of crustal events with magnitude greater than 3, which are then projected onto the seismic sections, this research aims to identify the distribution, type and geometry of active crustal faults and their possible continuation into the upper mantle. This will help evaluate the spatial relationships between crustal and mantle seismicity, and implicitly, between the mechanical relationship of the crust and uppermost mantle lithosphere. These observations appear to argue against recent models for west-dipping subduction of oceanic lithosphere at or in the vicinity of the Vrancea seismogenic. Since there seems to be a mechanical coupling between the foreland crust and upper mantle, one possible explanation for the geodynamic origin of the Vrancea zone could be partial delamination of the continental lithosphere in an intra-plate setting along a sub-horizontal lithospheric interface in the Carpathian hinterland that involves a remnant lithospheric coupling between the crust and uppermost mantle in the foreland.
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
DE: 1734 Seismology
DE: 1744 Tectonophysics
DE: 1208 Crustal movements--intraplate (8110)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting