Ortiz, Hugo

Volcano infrasound is an important component of multi-disciplinary volcano geophysics and has proven utility for tracking eruptive activity and quantifying eruption dynamics. Unfortunately, a major limitation in our interpretation of volcano infrasound is that it is critically affected by the morphology of the volcanic crater, which can transform potentially simple source-time functions occurring within the crater into a signal that is substantially more complex. If infrasound waveforms are to be used to recover important physical parameters about an eruption source, then a robust understanding of the acoustic response of the crater is required. In many cases, and especially for large deep craters, the acoustic response function acts as a severe filter. For example, at Cotopaxi Volcano (Ecuador) infrasound ‘tornillos’ with an impulsive onset and peaked spectra at 0.2 Hz decaying for more than 90 s are part of the source response due to the crater’s steep-walled, deep crater. We analyze broadband infrasound data from open-vent volcanoes with a wide variety of crater geometries and jointly calculate their crater acoustic response using 1-D (axisymmetric) and 3-D morphologies derived from structure-from-motion digital terrain models. We analyze both explosion and lava lake infrasound from Villarrica (Chile), Stromboli (Italy), and Nyiragongo (Democratic Republic of the Congo) to demonstrate a broad spectrum of volcano infrasound, whose attributes are heavily influenced by crater shape. We demonstrate how some differences between simulations and recorded explosion are influenced by sourcetime functions, which may range from brief and impulsive to complicated or extended in time. Numerical modeling shows that each volcanic crater has a unique impulse response and that deconvolving this acoustic response is vital for estimating important eruption parameters including the size of volcanic explosions.