Size of Popocatepetl volcano explosions (1997-2001) from waveform inversion

Several volcanic explosions have been recorded since April 1997 at broadban d seismic stations located around the Popocatepetl volcano, Mexico. We have inverted waveforms of ten of these explosions to estimate the following so urce parameters: depth, duration, magnitude and direction of the single for ce, F. The crustal structure used in generating Green's function at nearest stations is derived from the inversion of teleseismic receiver functions a t the broadband permanent station PPIG, located 5 km north of the volcano. This inversion reveals a low velocity zone at similar to8 km beneath the su mmit with high Poisson ratio, possibly related to the magma chamber. We fin d that F scales with tau, the duration of the source-time function, as F pr oportional to tau (2). Based on this relationship we determine an impulse m agnitude scale, M-k. This magnitude is tied to the Mount Saint Helens initi al explosive phase of May 18, 1980, whose magnitude is estimated as 4.6. M- k, of the ten Popocatepetl explosions ranges between 1.8 and 3.2. Finally, we also propose an equivalent formula for rapid estimation of magnitude of future Popocatepetl explosions, which requires filtered amplitudes at PPIG.