The First Detection of an Earthquake From a Balloon Using Its Acoustic Signature

Extreme temperature and pressure conditions on the surface of Venus present formidable technological challenges against performing ground‐based seismology. Efficient coupling between the Venusian atmosphere and the solid planet theoretically allows the study of seismically generated acoustic waves using balloons in the upper atmosphere, where conditions are far more clement. However, earthquake detection from a balloon has never been demonstrated. We present the first detection of an earthquake from a balloon‐borne microbarometer near Ridgecrest, CA in July 2019 and include a detailed analysis of the dependence of seismic infrasound, as measured from a balloon on earthquake source parameters, topography, and crustal and atmospheric structure. Our comprehensive analysis of seismo‐acoustic phenomenology demonstrates that seismic activity is detectable from a high‐altitude platform on Earth, and that Rayleigh wave‐induced infrasound can be used to constrain subsurface velocities, paving the way for the detection and characterization of such signals on Venus. Plain Language Summary The interior structure of Venus remains unknown due to lack of in situ seismic observations. Adverse temperature and pressure conditions on the Venusian surface limit the lifetimes of landers to a few hours, which poses a technological challenge against performing ground‐based seismology to detect venusquakes. Seismic energy on Venus, as on Earth, can be transmitted into the atmosphere through mechanical coupling and propagate as low‐frequency sound (infrasound). Infrasound from earthquakes travels long distances and has been detected from ground‐based stations. This mechanism may allow the detection of seismically generated pressure disturbances on Venus using balloons, enabling remote seismology from its upper atmosphere, where temperature and pressure conditions are far more clement and longer mission lifetimes are likely. However, the feasibility of such a technique has yet to be established through the detection of ground motion following an earthquake using a freely floating balloon. We demonstrate the first detection of an earthquake from a high‐altitude balloon. We explore the dependence of the pressure signal seen by the balloon on parameters such as the magnitude, focal mechanism, location of the earthquake, surface topography, and atmospheric structure. We also show how the signal recorded at the balloon can be used to study the subsurface. Key Points First detection of a