Resonant coupling between the Earth and the atmosphere at frequencies where the solid Earth modes overlap the fundamental modes of the atmosphere allows for the triggering of oscillatory acoustic perturbations by ground excitation and vice versa. Here, we describe oscillatory perturbations observed in the solid Earth (from volumetric borehole strainmeter data) and in the atmosphere (from GPS-derived ionospheric total electron content) following the 2003 July 13, Soufriere Hills Volcano explosion (Montserrat, Lesser Antilles). Spectral analysis shows an amplitude peak at 4 mHz for both data sets, with similar waveforms and signal duration. Using a normal mode summation technique, we show that both signals are explained by a single explosive source in the atmosphere. Similarities in waveforms, in particular a double wave train also reported after several other explosion-triggered atmospheric perturbations, result from the superposition of the dominant (fundamental) atmospheric modes that trigger resonant coupling with the solid Earth around 4 mHz.
Dautermann, Thomas Calais, Eric Lognonne, Philippe Mattioli, Glen S.