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Inversion of seismic and gravity data to infer the density and thermal structure under the European continent

Final Activity Report Summary - DATEC (Inversion of seismic and gravity data to infer the density and thermal structure under the European continent)

Within the first year of this project, tomographic inversion of P body waves, fundamental mode Love and Rayleigh wave group speed measurements, and gravity data allow us to reconstruct Vp, Vs and upper mantle density structure below the Euro-Mediterranean area, down to 250 depth. PM0.5 P-wave tomography of the Alpine-Mediterranean area (Piromallo and Morelli, 2003) and the new transversely isotropic shear wave velocity model of the upper mantle in the European and Mediterranean region (Schivardi and Morelli, 2007) are inverted with the Bouguer anomalies computed from the satellite GGM02C (Tapley et al., 2005) high resolution global gravity model.

The approach uses a probability density function, where the information given by the seismic model and the information on the physical correlation among the density and the velocity parameters limit the model space within that the inversion of gravity data can operate. The density model parametrisation which uses polyhedral bodies whose density is linearly dependent on the three coordinates (Pohànka, 1998) leads to a perfect match between the density and the velocity models and takes into account the presence of structures characterized by a gradual increase in density with depth.

Taking in account the data resolution, we define the cell model with a horizontal regular spacing of 1° x 1°. The model horizontal dimensions are approximately of 6600 km in E-W direction, 3900 km in N-S direction. The vertical spacing is 50 km. The parallelisation of the codes allow the inversion of fully populated matrices with 50,000 x 50,000 values.

Accurate investigation of the physical relationships between Vp, Vs and bulk densities for the crust and the upper mantle up to 300 km have been conducted considering the information of both seismological and gravity data. This analysis can open new avenues for research in seismology, in those fields where the above physical relationships are needed.