Using a new method to evalute Green's functions for elastic layered media, we compute complete synthetic seismograms of regional distances for an earthquake in the earth crust. We choose source parameters the ones inferred for an earthquake in central France and compare the computed seismograms to the ones recorded at several short-period stations of the French seismic network. The major features of the records including complexity and duration are well reproduced by the synthetics. Lg waves, which are the prominant phase, are shown to be guided waves made up to SH and SV waves incident on the Moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust. The length of the computed Lg wave coda extends between group velocities of 3.5 and 2.8 km/s and is in good agreement with the data.