Geophysicist Tieyuan Zhu of Penn State and colleagues analyzed two and a half years of seismic data collected by fiber-optic cables beneath the University Park campus in State College, Pennsylvania. The cables, buried about one meter underground across roughly four kilometers, detected more than 450 thunderquakes — ground vibrations caused by acoustic pressure waves from thunderstorms transferring energy into the earth.
The team converted these signals into images of the near-surface geology down to approximately 100 meters depth. The campus sits on a karstic landscape characterized by limestone caverns and fractures. The new imagery revealed several previously undetected weak zones in the limestone bedrock.
Findings were corroborated using borehole logs drilled into the ground and satellite measurements of surface deformation. The 2019 study by the same group had demonstrated that fiber-optic cables could detect thunder-generated seismic waves; the current work extends that capability to subsurface imaging.
Because thunderstorms produce strong signals covering tens of square kilometers per event, the researchers suggest thunderquakes could be cheaper and easier than traditional seismic surveys, especially in urban areas with existing fiber-optic networks. Zhu also noted the potential for using thunderquakes for seismic surveys on other planetary bodies, such as Saturn's moon Titan, which experiences long-lasting megastorms.
The study was published August 21 in Science Advances.
‘Thunderquakes’ do more than shake the ground — they map it
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