Seismic sensors measure soil moisture in vadose zone

The vadose zone is crucial for plants and crops to obtain water through their roots, but measuring how this underground moisture fluctuates over time and between geographical regions has traditionally relied on satellite imaging that provides low-resolution averages and cannot penetrate below the surface. Additionally, moisture within the vadose zone changes rapidly, such as when a thunderstorm saturates a region that dries out a few days later.

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The new method from Caltech (California Institute of Technology) is said to rely on seismic technology that can detect the vibrations of human activity such as traffic. As these vibrations pass through the ground, they are slowed down by the presence of water. The new study measures the water content in the vadose zone through seismic rumblings from everyday traffic. 

The research is a collaboration between the laboratories of hydrologist Xiaojing (Ruby) Fu, assistant professor of mechanical and civil engineering; and seismologist Zhongwen Zhan, professor of geophysics. The work is detailed in Nature Communications.