Location: Watershed Physical Processes ResearchTitle: Feasibility of using a seismic surface wave method to study seasonal and weather effects on shallow surface soils Author
Submitted to: Journal of Environmental & Engineering Geophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2013
Publication Date: 6/26/2014
Citation: Lu, Z. 2014. Feasibility of using a seismic surface wave method to study seasonal and weather effects on shallow surface soils. Journal of Environmental & Engineering Geophysics. 19(2):71-85. Interpretive Summary: This work was to develop a new seismic surface wave method; laser Doppler vibrometer (LDV) based multichannel analysis of surface wave (MASW) method to noninvasively measure and image the shear S-wave velocity of the subsurface soil to the depth of 2.5 meters below the surface. With the LDV-based MASW method, a long-term survey was conducted to measure and monitor the temporal variations of the S-wave velocity due to seasonal and weather effects. The study shows that the S-wave image can reflect the variations due to seasonal transitions and weather events that are correlated with the water potential and water content. The correlations between the S-wave velocity and the soil hydrologic properties can be understood using the concept of the effective stress for unsaturated soils. The results of the work demonstrated that the LDV-based MASW method can be used for non-invasively water potential and water content measurement and visualization for subsurface soils.
Technical Abstract: The objective of the paper is to study the temporal variations of the subsurface soil properties due to seasonal and weather effects using a combination of a new seismic surface method and an existing acoustic probe system. A laser Doppler vibrometer (LDV) based multi-channel analysis of surface wave (MASW) method is developed to measure the soil profile in terms of the shear wave velocity at depths up to a few meters. While the conventional MASWs use geophones as surface vibration sensors, the present MASW uses a moving LDV as a non-contact sensor to detect Rayleigh wave propagation generated by an electromagnetic shaker operating in a chirp mode. A long-term survey was conducted by measuring the S-wave velocity profile with the MASW along with the measurements of soil temperature, water content, water potential, and the P-wave velocity with the existing acoustic probe system. The results from the two methods are compared and interpreted with the concept of the effective stress that is governed by soil suction stress for top unsaturated soils and overburden pressure for deeper layer of soils. This study demonstrates that the S-wave velocity images obtained from the LDV-MASW method can effectively monitoring the temporal and spatial variations of the subsurface soil properties in vadose zone.