Abstract
A volcanic eruption transmits both seismic and infrasound signals. The seismo-acoustic power ratio is widely used to investigate the eruption behaviors and the source dynamics. It is often the case that seismic data during an eruption are significantly contaminated or even dominated by ground shaking due to infrasound (air-to-ground signals). To evaluate the contribution of infrasound-originated power in the seismic data, we need a response function of the seismic station to infrasound. It is rare to obtain a seismo-acoustic data set containing only infrasound signals, though it is ideal for calculating the response function. This study proposes a simple way to calculate the response function using seismo-acoustic data containing infrasound and independent seismic waves. The method requires data recorded at a single station and mainly uses the cross-correlation function between the infrasound data and the Hilbert transform of the seismic data. It is tested with data recorded by a station at Kirishima volcano, Japan, of which response function has been constrained. It is shown that the method calculates a proper response function even when the seismic data contain more significant seismic power (or noise) than the air-to-ground signals. The proposed method will be useful in monitoring and understanding eruption behaviors using seismo-acoustic observations.
Highlights
IntroductionA propagating acoustic wave in the atmosphere induces local ground oscillation (Ben-Menahem and Singh 1981; Sabatier et al 1986)
The air-to-ground signals recorded by seismometers are used to investigate infrasound when few Ichihara et al Earth, Planets and Space (2021) 73:180 infrasound sensors are available (Johnson and Malone 2007; Ichihara et al 2012; De Angelis et al 2012; McKee et al 2018)
We propose to use the response function to examine the contribution of the air-to-ground signals in the Volcanic Acoustic–Seismic Ratio (VASR) of data to assess the seismic–infrasonic energy partitioning more appropriately
Summary
A propagating acoustic wave in the atmosphere induces local ground oscillation (Ben-Menahem and Singh 1981; Sabatier et al 1986). It is recorded by infrasound sensors and by seismic sensors. The generation efficiency of the air-to-ground signal is ∼ 0.1 − 10 μm/s/Pa (Ichihara 2016; Novoselov et al 2020), which is much larger than that of the groundto-air signal (∼ 0.0003 Pa/(μm/s)) (e.g., Kim et al 2004; Watada et al 2006; Ichihara et al 2012; Kurokawa and Ichihara 2020) The former is usually more significant in the seismo-acoustic observation during volcanic eruptions. They can produce significant power in the seismometer records and disturb the analyses of seismic signals associated with eruptions (Nakamichi et al 2013; Ichihara (2016) and other surface phenomena, such as snow avalanches (Heck et al 2019; Marchetti et al 2020)
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