Researchers use thunder and fiber-optic cables for seismic imaging
Scientists used thunder-induced seismic waves and fiber-optic cables to study Earth's near-surface structure, testing their approach with real storms at Penn State.
Researchers have developed a way to use thunder as a seismic source and fiber-optic cables as sensors to study the structure of Earth's near-surface layers. The approach relies on recording how acoustic shock waves from thunder interact with the ground. When these waves strike soft soil, hard rock, or human-made infrastructure, the way energy propagates changes. Part of the energy is converted into Rayleigh waves, which travel along the surface, while the rest penetrates deeper through loose material or underlying bedrock.
To extract useful information, researchers need to know what seismic waves from a thunderclap should look like. That requires modeling several processes. Because each thunderquake is unique, depending on location and conditions, the model can only be an approximation. This inherent uncertainty may explain why such data were not analyzed earlier.
The team used SPECFEM3D Cartesian, software designed for 3D seismic wave reconstruction. The modeling involved compromises. The atmosphere was treated as a homogeneous layer 3.6 kilometers thick, even though the air near a thunderstorm is far from uniform. The software also updated events at a frequency lower than the speed of waves at the Earth-air interface. To compensate, researchers stretched the top 20 meters of the Earth model to span 200 meters.
To test the model, the scientists used real thunderstorms that passed over their campus. A useful discovery in seismology is that standard fiber-optic cables can act as seismometers. Penn State University has a 4-kilometer fiber line under its campus dedicated to seismic sensing. The campus is located in a part of the United States where summer thunderstorms are common, providing a convenient testing ground.
