Synthetic tsunami motion in ealistic oceanic media

Financial support from GNDT (contract 94.01703-PF54), MURST (40% and 60% funds), EEC Contract EV5V-CT94-0491Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

The meaning of surface wave dispersion curves in weakly laterally varying structures

The analysis of surface wave dispersion is efficiently applied to estimate 1D subsurface velocity profiles. The same approach is even applied at sites that present weak lateral variations under the assumption that the estimated dispersion curve is representative of the average properties beneath the receiver spread. We verify this assumption by discussing the meaning of the dispersion curve in weakly laterally varying structures using the path-average approximation (PAVA). Using PAVA we compute synthetic data for different lateral variations and we extract dispersion curves using the f-k wavefield transform. If the phase slowness is linearly varying along the propagation path and the wavenumber resolution of the measuring array does not allow for separating the different wavenumbers of the propagating surface waves, the estimated dispersion curve provides the average slowness. On the contrary, if the phase slowness is not linearly varying or if the wavenumber resolution of the measuring array is enough to discriminate the wavenumbers, the retrieved dispersion curve does not represent any specific velocity of the subsurface. To mitigate this problem windowing can be successfully adopted to make the retrieved dispersion curve representative of the local property of a subsoil column that coincides with the window maximum

Caveats on tomographic images

Geological and geodynamic models of the mantle often rely on joint interpretations of published seismic tomography images and petrological/geochemical data. This approach tends to neglect the fundamental limitations of, and uncertainties in, seismic tomography results. These limitations and uncertainties involve theory, correcting for the crust, the lack of rays throughout much of the mantle, the difficulty in obtaining the true strength of anomalies, choice of what background model to subtract to reveal anomalies, and what cross-sections to select for publication. The aim of this review is to provide a relatively non-technical summary of the most important of these problems, collected together in a single paper, and presented in a form accessible to non-seismologists. Appreciation of these issues is essential if final geodynamic models are to be robust, and required by the scientific observations