Monitoring the critical zone with ambient seismic noise recorded on a dense nodal array

Soil moisture is a key parameter in the Critical Zone (CZ), the region of the shallow subsurface which governs key ecosystem services including agriculture and water management.

Geophysical investigations of the CZ have so far predominantly focused on static imaging studies. Passive seismic techniques exploiting ambient seismic noise allow us to monitor changes over time as well as space by analysing changes in relative seismic velocity across a network of sensors. This method has been shown effective in monitoring groundwater fluctuations at watershed-scale resolutions comparable to remote sensing by satellite.

Using a new type of sensor known as a nodal seismometer we extend the ambient noise method to high temporal and spatial resolutions of 30 minutes and 10 metres. This study site is co-located with a monitoring station providing rich hydrometeorological data, allowing researchers to compare how changing environmental factors are reflected in seismic velocity at field scale. Researchers find a correlation between seismic velocity and soil moisture, opening the opportunity for using this new technology to quickly deploy flexible monitoring systems at scales useful for agricultural applications.