Analysis of air-ground coupling using seismo-acoustic cross-spectral analysis

Abstract

Air-ground and ground-air coupling are key processes in the rapidly developing field of seismo-acoustics and are particularly relevant in volcano geophysics. Volcanic eruptions often simultaneously generate sustained seismic and infrasonic signals, e.g., by fluid flow simultaneously occurring in the subsurface and atmosphere. Building upon recent work by Ichihara etal. (2012), we show that cross correlation, coherence, and cross-phase spectra between waveforms from nearly collocated seismic and infrasonic sensors provide new information about air-ground and ground-air coupling. Combining this method with infrasound array processing can provide insight into the geophysical processes generating a range of seismo-acoustic signals. For example, we show that seismic tremor recorded during an eruption at Mount St. Helens is dominated by air-ground coupled infrasound between 5 and 15 Hz. We anticipate that cross-spectral analysis and similar techniques will have wide applicability to arbitrary seismo-acoustic sources and in exploiting the growing volume of seismo-acoustic data. Ichihara et al. (2012), “Monitoring volcanic activity using correlation patterns between infrasound and ground motion,” Geophys. Res. Lett. 39, L04304, doi:10.1029/2011GL050542.