The regional propagation of two types of guided waves, the Lg wave and the fundamental mode of the Rayleigh wave, is studied experimentally. In the first part we process the data of the SISBALIG II experiment to study the Lg wave blockage in the Ligurian Sea (south-east of France). Using energy diagrams we find that the Lg wave extinction occurs in the zone of about 20 km width in the vicinity of the Provence Margin. Comparing the observations with numerical simulations we show that the diffraction of the energy into oceanic sediments is the most important factor adding into this extinction. In the second part we study the Rayleigh wave propagation and the crustal structure in southern Mexico. We use a cIassical approach consisting of the inversion of dispersion curves for the velocity structure. To measure group velocity dispersion curves we develop a logarithrnic stacking technique in the period-time or period-group velocity domain. We use a two-step inversion procedure: (1) Iinear inversion et (2) Monte-Carlo inversion. After measuring dispersion curves in different regions we invert them for local 1D velocity models. Finally, we construct a composed heterogeneous model of the cru st of the southern Mexico. It allows us to simulate the major features of the propagation of the waves emitted during earthquakes in the Middle America subduction zone. This way, we show that the regional amplification at periods of 8-10 s in the region of the Valley of Mexico is due to the presence of a shallow low-velocity layer in the southem part of the Mexican VoIcanic Belt.
