Acoustic source inversion to estimate volume flux from volcanic explosions

Abstract

We present an acoustic waveform inversion technique for infrasound data to estimate volume fluxes from volcanic eruptions. Previous inversion techniques have been limited by the use of a 1‐D Green's function in a free space or half space, which depends only on the source‐receiver distance and neglects volcanic topography. Our method exploits full 3‐D Green's functions computed by a numerical method that takes into account realistic topographic scattering. We apply this method to vulcanian eruptions at Sakurajima Volcano, Japan. Our inversion results produce excellent waveform fits to field observations and demonstrate that full 3‐D Green's functions are necessary for accurate volume flux inversion. Conventional inversions without consideration of topographic propagation effects may lead to large errors in the source parameter estimate. The presented inversion technique will substantially improve the accuracy of eruption source parameter estimation (cf. mass eruption rate) during volcanic eruptions and provide critical constraints for volcanic eruption dynamics and ash dispersal forecasting for aviation safety. Application of this approach to chemical and nuclear explosions will also provide valuable source information (e.g., the amount of energy released) previously unavailable.

Waveform inversion of acoustic waves for explosion yield estimation

“…However, in a realistic atmosphere, acoustic wave propagation is significantly affected by atmospheric layered structure, wind, and topography (e.g., mountains and buildings). The waveform inversion technique [Ohminato et al, 1998;Kim et al, 2015] can be used to infer the optimal acoustic source time function for the observed overpressure waveforms. Alternatively, it can be directly obtained from mass flow history of equivalent acoustic source (ṁ(w, t)).…”

“…Acoustic wave interaction with atmospheric structure and topography must be considered to compute accurate Green's functions, which is critical to the accuracy of obtained source time function [Kim et al, 2015]. Acoustic wave interaction with atmospheric structure and topography must be considered to compute accurate Green's functions, which is critical to the accuracy of obtained source time function [Kim et al, 2015].…”

Using infrasound to constrain ash plume rise

“…In this and previous studies, the effects of variable atmosphere, vent geometry, and the local topography on the propagation of infrasound are neglected. Numerical techniques such as finite-difference time-domain can be employed due to their ability to handle complicated phenomena in infrasound propagation, thus allowing inclusion of the effects of topography Lacanna et al 2014;Kim et al 2015).…”

Diverse Eruptive Activity Revealed by Acoustic and Electromagnetic Observations of the 14 July 2013 Intense Vulcanian Eruption of Tungurahua Volcano, Ecuador

“…Infrasound source processes can often be resolved in detail because path effects on infrasound near the vent are often small (Fee & Garces, 2007;Johnson & Lees, 2010) or predictable and straightforward to correct (Kim et al, 2015). Infrasound source processes can often be resolved in detail because path effects on infrasound near the vent are often small (Fee & Garces, 2007;Johnson & Lees, 2010) or predictable and straightforward to correct (Kim et al, 2015).…”

“…Its activity included strombolian, vulcanian, and subplinian explosions separated by intervals with weak or absent surface activity (Arellano et al, 2008;Hall et al, 2015). The asymmetry of Tungurahua's crater and summit ( Figure 1) focuses infrasound northwest and complicates recordings (Kim et al, 2012); these effects can be removed with numeric wave propagation modeling (Kim et al, 2015). The asymmetry of Tungurahua's crater and summit ( Figure 1) focuses infrasound northwest and complicates recordings (Kim et al, 2012); these effects can be removed with numeric wave propagation modeling (Kim et al, 2015).…”