Mapping Subsurface Structures with Thunderquakes
Scientists use seismic waves from lightning strikes to image underground formations.
1The Seismic Impact of Lightning
When lightning strikes, it superheats the surrounding air, creating a shock wave. While this wave is heard as thunder in the atmosphere, part of it reaches the ground and converts into seismic waves. These 'thunderquakes' ripple through subsurface soil and rock. Researchers have harnessed this phenomenon to map underground structures with unprecedented detail.
2Fiber-Optic Sensor Network
The Penn State FORESEE project utilized a 2.5-mile-long fiber-optic cable transformed into 2,100+ vibration sensors using distributed acoustic sensing technology. Spaced just meters apart, these sensors created a high-resolution seismic monitoring array capable of detecting minute ground movements caused by atmospheric events.
3Recording 458 Thunderquakes
Over two years, researchers recorded 458 distinct thunderquake events using repurposed telecom infrastructure. The data revealed how atmospheric sound waves interact with subsurface geology. Particularly valuable were 'air-coupled Rayleigh waves' that carried information about features up to 100 meters deep.
4Seismic Dispersion Technique
By analyzing how different frequency waves travel at varying speeds through subsurface layers (seismic dispersion), the team reconstructed underground profiles without drilling. This approach generated X-ray-like images of the top 100 meters of Earth's crust using only natural lightning energy.
5Alternative to Traditional Surveys
Conventional subsurface imaging requires truck-mounted vibroseis units or extensive sensor arrays. Thunderquakes provide natural energy sources, while existing global fiber-optic networks serve as ready-made sensor arrays. This combination enables continuous, large-area monitoring without specialized equipment.
6Pennsylvania's Karst Features
In State College's limestone/dolomite terrain, thunderquake data identified four distinct slow-velocity zones indicating fractures or voids. Two zones correlated with satellite-detected subsidence areas. The findings demonstrate how this method can pinpoint potential sinkhole risks in water-soluble bedrock formations.
7Global Application Potential
With karst landscapes covering 20% of Earth's land area and affecting 25% of the population, this technique could revolutionize hazard mapping. Urban planners could identify subsidence risks before construction begins, potentially preventing infrastructure damage from sinkholes or groundwater contamination.
8Extraterrestrial Applications
The principle of atmospheric energy conversion might extend beyond Earth. On Titan (Saturn's moon and target of NASA's Dragonfly mission), lightning-induced seismic waves could probe subsurface structures where conventional quakes are rare. Volcanic eruptions and meteor airbursts might similarly serve as seismic sources on other worlds.
Original article: Scientific American Content: Global — Yıldırım Depremleriyle Yeraltı Haritalama