HR: 1340h
AN: NG43B-0575    [Abstracts]
TI: The 3-D Vrancea Seismogenic Zone Revealed by Joint Inversion of P and S Traveltimes and Gravity Measurements: Synthetic Examples and Preliminary Experimental Results
AU: * Tondi, R
EM: rosaria@eost.u-strasbg.fr
AF: EOST, Ecole et Observatoire des Sciences de la Terre, 5 rue René Descartes, Strasbourg, 67100 France
AU: Achauer, U
EM: ulrich.achauer@eost.u-strasbg.fr
AF: EOST, Ecole et Observatoire des Sciences de la Terre, 5 rue René Descartes, Strasbourg, 67100 France
AB: The aim is to provide new insights into the post-collisional processes of descending slab in the area of the southeast Carpathians in Romania called Vrancea.
Information from previous high-resolution teleseismic or local tomography (Martin and Ritter, 2005, Oncescu, 1984) allow us to build the Vp and Vs starting models, which we use for our investigations. The models cover a volume of 230 x 230 x 230 km³ and contain both shallow small-scale heterogeneities and large-scale structures down to the asthenospheric level. The source-receiver survey geometries of the VRANCEA99 (Hauser et al, 2001) and VRANCEA2001 (Landes et al., 2004) seismic refraction experiments are used for modelling the upper crust of the Carpathian orogen and the stations distribution of the CALIXTO (Carpathian Arc Lithosphere X Tomography, EOS, 1998) experiment is used to reconstruct the main seismic velocity contrasts in the investigated volume. The a priori models of CRUST2.0 (Bassin et al., 2000) and 3SMAC (Nataf et al., 1994) are used for transforming the velocity models in a density model. Pressure dependence is entering through the background density, which is depth-dependent. The inversion scheme is based on the methodology proposed by Tondi et al. (2000), now extended to S waves. The approach, now significantly improved, allows the reconstruction of both velocity and density structures, while reducing travel times and gravity residuals. As in this application we consider also seismological events, our strategy is to first locate P and S wave sources of local earthquakes and then consider these events as those originated from fixed source points. The events are iteratively relocated with the updated velocity models until the discrepancies between two subsequent localizations are sufficiently small. Eventually, the used inversion scheme allows us to recover a density model which is equally compatible with Vp and Vs models.
The syntethic tests show how this analysis can be successful in giving insights on the upper limit of the subducting slab of oceanic lithosphere, and how it opens new avenues for research in seismology in those fields where the correct physical relationships between Vp, ρ, and Vs are needed. First results on the analysis of the local events with magnitude M_l > 2.0, recorded from May to November 1999, as well as of the datasets acquired during the refraction experiments, and of the measurements taken from the Romanian gravity map (Ioane and Radu, 1995) are also presented.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3260 Inverse theory
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 7270 Tomography (6982, 8180)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005