  An array of ten broadband stations was installed on the Popocat\'epetl
volcano (Mexico) for five months between October 2002 and February 2003. 26
regional and teleseismic earthquakes were selected and filtered in the
frequency time domain to extract the fundamental mode of the Rayleigh wave. The
average dispersion curve was obtained in two steps. Firstly, phase velocities
were measured in the period range [2-50] s from the phase difference between
pairs of stations, using Wiener filtering. Secondly, the average dispersion
curve was calculated by combining observations from all events in order to
reduce diffraction effects. The inversion of the mean phase velocity yielded a
crustal model for the volcano which is consistent with previous models of the
Mexican Volcanic Belt. The overall crustal structure beneath Popocat\'epetl is
therefore not different from the surrounding area, and the velocities in the
lower crust are confirmed to be relatively low. Lateral variations of the
structure were also investigated by dividing the network into four parts and by
applying the same procedure to each sub-array. No well-defined anomalies
appeared for the two sub-arrays for which it was possible to measure a
dispersion curve. However, dispersion curves associated with individual events
reveal important diffraction for 6 s to 12 s periods which could correspond to
strong lateral variations at 5 to 10 km depth.
