A Midsummer Flights’ Dream: Balloon-borne infrasound-based aerial seismology

Aerial seismology (AS) consists in detecting and characterizing atmospheric infrasound induced by ground displacements. Several studies have demonstrated that seismo-acoustic infrasound is highly similar to the seismic ground motion, making it a viable alternative for seismology on planetary bodies where deploying seismometers is technologically challenging. Until recently, such experiments were restricted to artificially-generated seismic events. However, on July 22, 2019, Brissaud et al. detected for the first time the infrasonic signature of a magnitude 4.2 earthquake from a high-altitude solar-heated balloon. In order to further demonstrate the feasibility of AS, additional detections are needed. Using similar balloons and payloads, stratospheric flights were launched several times per week during the summer of 2021 over Oklahoma’s seismogenic zone. In this work, we present this campaign and its initial results. We describe the flight system, instrumentation, and details of the campaign design. We focus on the possible detections of earthquakes during the campaign using numerical simulations. For selected events, we present the balloon pressure data and extract potential arrivals. We perform full-waveform simulations using SPECFEM2D-DG to confirm those arrivals. We conclude with statistical arguments for earthquake detections and recommendations for future flights. Earthquakes are numerous in Oklahoma, but are of low and decreasing magnitudes. Nonetheless, this campaign’s dataset is unique for the development of AS.