Unlocking the secrets of earthquakes with stratospheric balloons

A new approach to studying earthquakes from the stratosphere

A team of researchers, led by Solène Gerier, a PhD in Earth and solid planet sciences, applied mathematics engineer and post-doctoral fellow at ISAE-SUPAERO, has taken an important step forward in earthquake analysis. Their study focuses on the analysis of acoustic waves generated by earthquakes, using an innovative capture method for the object of study. The waves were recorded in the stratosphere using pressure sensors installed on high-altitude balloons. This new approach makes it possible to study earthquakes by analyzing the infrasound signals they emit through the atmosphere.

It builds on the pioneering work of Raphaël Garcia, a teacher-researcher at ISAE-SUPAERO specializing in space and planetary seismology. In 2022, he and his team demonstrated in Geophysical Research Letter the feasibility of such observations during the CNES Stratéole-2 mission in collaboration with the Laboratoire de Météorologie Dynamique. The breakthrough proposed by Solène Gerier enables the seismic source of these signals to be traced, analyzing only the acoustic contributions in the atmosphere.

Complex modeling to decipher signals

To disentangle the various components of the recorded signals, the scientist and her team have developed a sophisticated model. This incorporates not only infrasound ray tracings, but also background noise analysis and the response of “balloon platforms”. A complementary analysis was carried out to better understand the origin of the signals, involving not only the infrasound ray tracing technique, but also an analysis of the noise linked to balloon platform movements.

Simulations, carried out using SPECFEM2D-DG-LNS software, revealed that the wave signature was mainly influenced by the characteristics of the earthquake and the earth’s internal structure, and not by atmospheric conditions. "Ground vibrations produce acoustic waves that can be detected in the atmosphere. These waves have a particular signature because they were produced by seismic waves, which are themselves characteristic of the earthquake and the nature of the ground in which they propagate”, explains Solène Gerier. Modeling has enabled us to verify that these characteristics are preserved even in the atmosphere".

Promising results

While the simulations were unable to reproduce exactly the waveforms observed in the 0.05-0.3 Hz frequency band, they did reveal some interesting phenomena. In particular, the researchers observed a dispersion of seismic surface waves in the pressure recordings. The prolonged oscillations observed after the main signal can be explained in part by the complex vertical movements of the ground and the multiple reflections of infrasound off the topography.

Beyond its terrestrial application, this methodology could prove particularly valuable for the exploration of other planets, as Raphaël Garcia points out: “These platforms are interesting for planets on which we can’t deploy a seismometer on the surface because the atmosphere is too hot. This is particularly the case for the planet Venus (450 °C at the surface), for which we think that earthquakes will be detected in the future through the atmospheric disturbances they generate”.

This study, which follows on from research carried out by the Institute’s DEOS/SSPA team, demonstrates the considerable potential of airborne platforms for the study of earthquakes, both on Earth and on other planets.

To consult the scientific publication: https://earth-planets-space.springe...