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<p>The infrasonic array technique is applied in many volcanoes to locate the acoustic source. Compared to the azimuthal estimation for the horizontal source location information, the elevational estimation is challenging due to the difficulty of aligning sensors vertically. However, the elevational estimation is essential because volcanic eruptions often have infrasound sources distributed at different heights, such as a pyroclastic density current on a steep slope or a volcanic jet. A previous study, which conducted an infrasonic array experiment at Stromboli Volcano, obtained frequency-dependent source elevation, which they concluded to be due to the topographic effect on the apparent slowness along the ground. We examined the topographic effects on the apparent slowness by numerical simulations for acoustic propagation with the 2D axisymmetric finite element method. The simplification in 2D allowed us to examine the individual topographic elements around the vent and the array site at Stromboli Volcano. The mountain summit topography behind the array distorted acoustic phases, causing an underestimation of the slowness below 10&#xa0;Hz, which led to an apparent source at ≥ 100&#xa0;m above the vent. On the other hand, frequencies above 20&#xa0;Hz pointed to the right elevations. The comparison between the simulated and observed slowness-frequency relations indicated that the source was within 30&#xa0;m above the vent. We infer that turbulence in the atmosphere significantly above the vent should not be a primary source in the previous observation at Stromboli. We emphasize that considering the topographic effects is necessary to avoid misunderstanding the source location.</p> Graphical Abstract <p></p>

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Evaluation of topographic effects on infrasonic array observation toward the source elevation estimation

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年5月21日

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  • Kazuya Yamakawa,
  • Mie Ichihara,
  • Giorgio Lacanna,
  • Maurizio Ripepe

摘要

The infrasonic array technique is applied in many volcanoes to locate the acoustic source. Compared to the azimuthal estimation for the horizontal source location information, the elevational estimation is challenging due to the difficulty of aligning sensors vertically. However, the elevational estimation is essential because volcanic eruptions often have infrasound sources distributed at different heights, such as a pyroclastic density current on a steep slope or a volcanic jet. A previous study, which conducted an infrasonic array experiment at Stromboli Volcano, obtained frequency-dependent source elevation, which they concluded to be due to the topographic effect on the apparent slowness along the ground. We examined the topographic effects on the apparent slowness by numerical simulations for acoustic propagation with the 2D axisymmetric finite element method. The simplification in 2D allowed us to examine the individual topographic elements around the vent and the array site at Stromboli Volcano. The mountain summit topography behind the array distorted acoustic phases, causing an underestimation of the slowness below 10 Hz, which led to an apparent source at ≥ 100 m above the vent. On the other hand, frequencies above 20 Hz pointed to the right elevations. The comparison between the simulated and observed slowness-frequency relations indicated that the source was within 30 m above the vent. We infer that turbulence in the atmosphere significantly above the vent should not be a primary source in the previous observation at Stromboli. We emphasize that considering the topographic effects is necessary to avoid misunderstanding the source location.

Graphical Abstract