Abstract
The mechanical coupling between a planet and its atmosphere enables the
conversion of seismic waves into infrasound waves, i.e. low-frequency
pressure perturbations (< 20Hz), which propagate to the upper
atmosphere. Since the characteristics of the seismically-induced
pressure perturbations are connected to their seismic counterparts, they
provide a unique opportunity to investigate the atmospheric and interior
structures of a planet or to constrain source properties. However, in
Earth’s remote regions, deploying seismic or infrasound networks at the
surface can be a difficult task. Stratospheric balloon platforms
equipped with pressure sensors have therefore gained interest since they
provide a unique and inexpensive way to record pressure signals in the
atmosphere with a low noise level. Yet, infrasound observations of
Earthquakes on balloon platforms have never been reported in the
literature. In this study, we investigate the seismo-acoustic wavefield
generated by the aftershocks of the 2019 Ridgecrest sequence and other
regional low-magnitude Earthquakes on July 22 and August 9, 2019 using
four free-flying balloons equipped with pressure sensors. We observed a
strong signal coherence after the largest event between seismic motions
at the surface and balloon pressure variations which matches our
numerical simulations. A first atmospheric earthquake detection is
crucial to demonstrate the viability of this novel technique to monitor
infrasound from natural and artificial seismicity on Earth, and the
study of seismic activity on planets such as Venus.