Abstract
Atmospheric acoustic waves from volcanoes at infrasonic frequencies (0.01–20 Hz) can be used to estimate source parameters for hazard modeling, but signals are often distorted by wavefield interactions with topography, even at local recording distances (<15 km). We present new developments toward a simple empirical approach to estimate attenuation by topographic diffraction at reduced computational cost. We investigate the applicability of a thin screen diffraction relationship developed by Maekawa [1968, doi: https://doi.org/10.1016/0003-682X(68)90020- 0]. We use a 2D axisymmetric finite-difference method to show that this relationship accurately predicts power losses for infrasound diffraction over an idealized kilometer-scale screen; thus validating the scaling to infrasonic wavelengths. However, the Maekawa relationship overestimates attenuation for realistic volcano topography (using Sakurajima Volcano as an example). The attenuating effect of diffraction may be counteracted by constructive interference of multiple reflections along concave volcano slopes. We conclude that the Maekawa relationship is insufficient as formulated for volcano infrasound, and suggest modifications that may improve the prediction capability.
Highlights
Erupting volcanoes produce atmospheric acoustic waves dominant in the infrasonic frequency range („0.01–20 Hz) that can be used to detect, locate, and characterize ongoing eruptions, and to estimate important eruption source parameters [e.g. De Angelis et al 2019; Fee and Matoza 2013; Johnson and Ripepe 2011; Matoza et al 2019]
We found that the modeled acoustic power losses for the kilometer-scale screen are well-predicted by an empirically-derived re
The power losses are well predicted to first order for diffraction over the wedge and wide barrier, but the empirical relationship overpredicts losses for Sakurajima topography by „101 dB
Summary
Erupting volcanoes produce atmospheric acoustic waves dominant in the infrasonic frequency range („0.01–20 Hz) that can be used to detect, locate, and characterize ongoing eruptions, and to estimate important eruption source parameters [e.g. De Angelis et al 2019; Fee and Matoza 2013; Johnson and Ripepe 2011; Matoza et al 2019]. The simplest expression for acoustic power loss to diffraction assumes a single point of diffraction over a thin screen, as proposed by Maekawa [1968]. This relationship was empirically derived from experiments in which attenuation was estimated as the difference in sound pressure levels behind a rigid screen and the predicted values for free field propagation. Later studies incorporated the thin screen approximation into expressions for thick barriers [Fujiwara et al 1977] and wedges [Maekawa and Osaki 1985] These and various other numerical approaches [e.g. These and various other numerical approaches [e.g. Hadden and Pierce 1981; Pierce 1974] deal exclusively with audible-
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