Source and subsurface inversion using earthquake-generated infrasound recorded at a balloon platform: application to the 2021 Mw 7.3 Flores earthquake

Seismic waves can couple to the atmosphere and propagate as acoustic waves, including infrasound at frequency below 20 Hz. Seismically generated infrasound can be recorded by ground-based microbarometers, but also at higher-altitude by pressure sensors carried by balloons. Balloon-borne acoustic observations could be the key to exploring Venus' interior, as surface conditions do not allow for the deployment of seismometers. However, it remains unclear how much information about the subsurface is contained in seismically generated infrasound.  

In this contribution we use the recent earthquake-induced acoustic observations from a balloon network on Earth belonging to the Strateole2 campaign, following the 2021 Mw 7.3 earthquake in the Flores Sea, to invert for subsurface velocities. Seismic infrasound signals show body wave arrivals and surface wave dispersion similar to pure seismic signals recorded on the ground. Thus, beyond their detection capability, balloon infrasound also enables the use of classical inversion techniques to retrieve source and subsurface properties. We develop an inversion framework to jointly retrieve earthquake source location and seismic velocities of the subsurface based on arrival time measurements for P, S and Rayleigh waves at multiple balloon stations. We apply this approach to the Flores earthquake using data from four Strateole2 balloons.  

The inversion results are the probability density distribution of the seismic source location and of the subsurface velocities in a layered model. Both the resulting location and subsurface model are in good agreement with those obtained from traditional seismic data, confirming balloon seismology as a credible alternative for the seismic exploration of the Earth and other celestial bodies with atmospheres, such as Venus.