From atmospheric infrasound to the crust and mantle: Demonstrating subsurface inversion using balloon data

The atmosphere of the Earth allows for a coupling of seismic waves into acoustic waves, below the range of human hearing (infrasound). This process is expected to be sixty times stronger on our neighboring planet, Venus. Recent studies have shown that high-altitude balloon platforms offer an attractive solution for recording seismic infrasound in the harsh environment of Venus or in remote locations on Earth. This technology could thus be key to assessing seismic activity and subsurface properties in such areas. In this presentation, we present current advancements in balloon seismology, including recent detections of earthquake infrasound by stratospheric balloons on Earth. Balloon data have unique characteristics that must be accounted for in their analysis, such as specific infrasound noise characteristics, noise due to balloon buoyancy oscillations, as well as infrasound multipathing due to topography and other effects. Using a 2021 earthquake detected by multiple balloons on Earth, we demonstrate that balloon infrasound can successfully be used in a seismic inversion framework to jointly retrieve earthquake source location and seismic velocities of the subsurface. Results are in good agreement with those obtained with traditional seismic data. Based on these findings, we further explore seismo-acoustic coupling and infrasound propagation on Venus and the implications for prospective balloon seismology missions.