Infrasonic component of volcano-seismic eruption tremor

Abstract

Air-ground and ground-air elastic wave coupling are key processes in the rapidly developing field of seismoacoustics and are particularly relevant for volcanoes. During a sustained explosive volcanic eruption, it is typical to record a sustained broadband signal on seismometers, termed eruption tremor. Eruption tremor is usually attributed to a subsurface seismic source process, such as the upward migration of magma and gases through the shallow conduit and vent. However, it is now known that sustained explosive volcanic eruptions also generate powerful tremor signals in the atmosphere, termed infrasonic tremor. We investigate infrasonic tremor coupling down into the ground and its contribution to the observed seismic tremor. Our methodology builds on that proposed by Ichihara et al. (2012) and involves cross-correlation, coherence, and cross-phase spectra between waveforms from nearly collocated seismic and infrasonic sensors; we apply it to datasets from Mount St. Helens, Tungurahua, and Redoubt Volcanoes.

Using infrasound to constrain ash plume rise

“…Our model also differs from previous studies at other volcanoes such as Johnson (2007) and Matoza et al (2009). The former inferred that a monopole source best described pyroclastic explosions from Karymsky volcano, Russia.…”

“…Matoza et al (2009) contended that sustained eruption noise has its source in large scale turbulence, favouring a quadrupole source. However, the eruptions described by Matoza et al (2009) (2013); digital contour data available from Schaefer and Wallace (2012) collapse scar (Bull and Buurman 2013) which causes infrasound waves to interact with the wall around the vent during eruptions. For this reason a dipole source was deemed the most appropriate approximation for our calculations.…”

“…In contrast, only a handful of eruptions accompanied by atmospheric injection of vigorous, ash-rich plumes have been investigated to date (e.g. Caplan-Auerbach and McNutt 2010;Fee et al 2013;Mastin et al 2013;Matoza and Fee 2014;McNutt et al 2013;Ripepe et al 2013).…”

Site effect determination using seismic noise from Tungurahua volcano (Ecuador): implications for seismo-acoustic analysis

“…17(c). It suggests that other factors need to be taken into account to improve the soil response models of volcanic environments (Matoza & Fee 2014). Nevertheless the site correction improves our ability to decouple seismo-acoustic signals.…”

“…More recently, Ichihara et al (2012) proposed a method based on the cross-correlation of seismic and acoustic signals, to identify the coupling. Matoza & Fee (2014) extended this method to frequency domain using the coherence and applied it to study eruptions of Mount St Helens, Redoubt and Tungurahua volcanoes. Using our approach, removing the site effects improves the procedure of decoupling the acoustic signals mixed within the seismic record, yielding a better estimation of the seismic source energy.…”