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FRINATEK-Fri mat.,naturv.,tek

Airborne Inversion of Rayleigh waves

Alternative title: Luftbåren inversjon av Rayleigh-bølger

Awarded: NOK 8.0 mill.

Understanding a Venus' interior structure is critical to determine its origin and evolution and explain why conditions on this planet are so drastically different than on Earth. On Earth, seismic waves generated by seismic events such as Earthquakes and recorded by seismometers at the ground are utilized to constrain our planet down to its very core. However, deploying seismometers on Venus is significantly more technologically challenging due to its harsh surface conditions (more than 460°C and pressure near 90 atmos.). However, Venus conditions are fare more clements in the higher atmosphere (50-60 km alt.) where they are close to Earth conditions. Beyond Venus, deployments are also extremelly difficult in Earth's remote regions such as polar regions or over the Oceans where the subsurface is still poorly constrained. Could we deploy seismometers in the atmosphere to sense seismic waves? The short answer is yes! The same way a drum emits sound when it vibrates, Earth's surface generates inaudible acoustic waves, called infrasound, when an Earthquake hits. Exciting new developments have shown that the sound of seismic events can be recorded at high altitudes from a balloon and can inform us about the subusurface. However, very few seismic events have been detected from a balloon and we still ignore how much we can learn from these sound waves. AIR will address key theoretical and practical issues by taking advantage of balloon data collected by the Jet propulsion Laboratory and the Swedish Institute of Space Physics during large-scale balloon campaigns, and by relying on state-of-the-art simulation tools. The main objective is to build a model to automatically retrieve seismic source and subsurface structures from sound waves and explain how accurate this new technique can be for future planetary missions. AIR will empower balloons to explore distant worlds and provide unique insights on the deep underground in remote regions where current technology is lacking.

Our understanding of Earth's internal structure comes primarily from seismic waves that provide important constraints on subsurface seismic-velocity properties. However, traditional inversion methods cannot be implemented in regions of limited seismic-station coverage, in particular on Venus due to its harsh surface conditions but also in remote Earth regions. This lack of seismic data greatly limits our understanding of Venus’ origin and evolution, but also of the Earth’s subsurface. However, the mechanical coupling between the ground and its atmosphere enables the seismic energy to be transmitted into the atmosphere as low-frequency acoustic waves carrying information about the seismic source and the subsurface properties. While infrasound is traditionally recorded at ground-based stations, which suffers from the same in-situ deployment limitations as seismic stations, recent studies have demonstrated that balloon platforms can be used to monitor seismic activity from the atmosphere at a low operational cost. Balloon-borne seismology is a new dynamic field considered to be the only way to investigate Venus' interior. However, inversion of balloon-borne infrasound data has never been reported in the literature as field data are lacking and the coupling between seismic and acoustic waves in realistic media is poorly understood. Taking advantage of balloon pressure data collected by the Jet propulsion Laboratory and the Swedish Institute of Space Physics during large-scale balloon campaigns, the current project will address these key theoretical and practical issues by analyzing and modeling these seismically-induced infrasound signatures to retrieve the source and subsurface properties. AIR will first process and model the seismo-acoustic waves to analyze the field data. Results will then be injected in a statistical Bayesian inversion framework to retrieve uncertainties on source and subsurface properties and field-data processing from balloon campaigns.

Funding scheme:

FRINATEK-Fri mat.,naturv.,tek