Utilizing the solution of sound diffraction by a thin screen to evaluate infrasound waves attenuated around volcano topography

Abstract

The observation of infrasound signals in the vicinity of volcanoes is a powerful tool to understand the source of explosive volcanic activity. Although the propagation of infrasound signals is affected by the local topography, such effects are often ignored in the analysis, leading to potential misinterpretation of the source parameters. In this study, we propose a simple low-cost method of evaluating the attenuation of infrasound signals by topographical barriers. In this method, the first step approximates the elevation profile between the source and station into one thin screen-like barrier. Then, a mathematically exact solution of a sound diffraction problem is adopted to evaluate the attenuation of the infrasound amplitudes. To assess the validity of this method, the obtained estimates are compared with actual infrasound data observed at Sakurajima volcano, Japan. The results show that the estimates of relative amplitude to a reference station are more accurate than those considering only geometrical spreading, suggesting that the proposed method provides a useful first-order investigation of the attenuation of infrasound signals. The spatial distribution of the attenuation in the entire area of the volcano was also estimated, revealing a significant contrast between the eastern and western sides of the study area. Variations in signal attenuation also depend on the radial distance from the crater and were mainly attributed to variations of the relative screen height to the incident wavelength.