Prestack seismic data has been used in a new method to fully determine
thin-bed properties, including the estimation of its thickness, P-
and S-wave velocities, and density. The approach requires neither
phase information nor normal-moveout (NMO) corrections, and assumes
that the prestack seismic response of the thin layer can be isolated
using an offset-dependent time window. We obtained the amplitude-versus-angle
(AVA) response of the thin bed considering converted P-waves, S-waves,
and all the associated multiples. We carried out the estimation of
the thin-bed parameters in the frequency (amplitude spectrum) domain
using simulated annealing. In contrast to using zero-offset data,
the use of AVA data contributes to increase the robustness of this
inverse problem under noisy conditions, as well as to significantly
reduce its inherent nonuniqueness. To further reduce the nonuniqueness,
and as a means to incorporate a priori geologic or geophysical information
(e.g., well-log data), we imposed appropriate bounding constraints
to the parameters of the media lying above and below the thin bed,
which need not be known accurately. We tested the method by inverting
noisy synthetic gathers corresponding to simple wedge models. In
addition, we stochastically estimated the uncertainty of the solutions
by inverting different data sets that share the same model parameters
but are contaminated with different noise realizations. The results
suggest that thin beds can be characterized fully with a moderate
to high degree of confidence below tuning, even when using an approximate
wavelet spectrum.