The Volcano Acoustic Source: Decoupling Crater Modulation From Infrasound Signal

Volcanoes radiate intense sounds concentrated in the infrasound band, which is below the frequency threshold of human hearing. Such sounds are often recorded many kilometers from a volcano and are used by scientists and observatories to continuously observe eruptions; commonly infrasound is used to detect explosions and to measure eruption intensity and character. This study's objective is to improve the understanding of how infrasound relates to eruptive processes occurring within a volcanic crater. To implement infrasound as an effective tool it is necessary to understand how the recorded sound signals are modulated by crater shape. This work aims to measure, model, and quantify the influence of the crater's acoustic response, which influences the radiated sound much like the horn of a musical instrument. Measurements will include field work where the sound field is recorded both within and outside the craters of active volcanoes. Anticipated results will lead to improved modeling of eruptive processes and to better recognition of changes in volcanic unrest. This study will bring together a diverse international team spanning numerical, analytical, and field expertise from not just Idaho, but Hawaii, Chile, Italy, and the Democratic Republic of the Congo. The work will also fund graduate and undergraduate students, and contribute to exciting public outreach opportunities which include chronicling the efforts through a component of professional videographies.

The crater acoustic response is a transfer function, which relates source processes occurring at the bottom of a volcanic crater to the infrasound that is radiated to distant receivers. An understanding of the crater acoustic response is critical to improving utility of volcano infrasound recordings for both general monitoring and for improving physics-based eruption models. In cases where craters are deep and narrow and/or assymetric, the crater acoustic response can be particularly extreme and can significantly distort a source-time function. Deconvolution of the crater's acoustic response is thus critical to recovering accurate source-time functions. This study's integrated numerical modeling and field work, which incorporates large-N infrasound sampling, will permit robust quantification of the crater's sound modulation effects. Anticipated results will permit researchers to better infer source parameters and to invert for crater geometry, which may vary dynamically over time at active volcanoes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.