Seismic characterization of soil structure - field observations and modeling
Abstract
Soil structure results from biotic and abiotic processes that significantly alter soil mechanical and hydrological properties and many hydro-ecological soil functions. The mechanical component of soil structure is difficult to quantify by standard methods at the field scale, and we seek to harness the potential of seismic methods for expanding observation capabilities at spatial scales larger than traditional point measurements. Seismic velocities are affected by soil elastic properties, the saturation state, and water spatial distribution in the probed volume. These factors are linked to soil structure status (e.g., macroporositiy, mechanical impedance, and hydraulic conductivity), yet, we lack quantitative understanding on interpreting seismic signals to infer soil structure information. We conducted observations in a long-term soil structure observatory using an automated impact seismic source (center frequency of 200 Hz) to collect (1) seismic information from plots with different structure compaction levels with and without plant cover, and (2) time-lapse seiemic data at different periods. A 3.5 m long seismic array with geophone spacings of 0.1 and 0.2 m was deployed with the source at the center. Time-lapse observations revealed high correlations between apparent seismic velocities and water content (obtained from TDR probes). The standard rock-physics models fail to describe the observations due to the strong dependency of soil mechanical properties on water content. We adjust the Hertz-Mindlin contact model and use the Hashin-Shtrikman bounds to model the elastic moduli of dry soil matrix and gradually wet (three-phase medium) soil. The pedophysical seismic model is used to describe seismic observations under dynamic hydrologic conditions. The presentation will highlight effects of land cover (vegetation) and compaction states influencing the seismic observations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNS31A0767R
- Keywords:
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- 0402 Agricultural systems;
- BIOGEOSCIENCES;
- 1835 Hydrogeophysics;
- HYDROLOGY;
- 1842 Irrigation;
- HYDROLOGY