Comparing geophysical measurements to theoretical estimates for soil mixtures at211 low pressures

摘要

The authors obtained good estimates of measured velocities of sand-peat samples211u001eat low pressures by using a theoretical method, the self-consistent theory of 211u001eBerryman (1980), using sand and porous peat to represent the microstructure of 211u001ethe mixture. They were unable to obtain useful estimates with several other 211u001etheoretical approaches, because the properties of the quartz, air and peat 211u001ecomponents of the samples vary over several orders of magnitude. Methods that are 211u001euseful for consolidated rock cannot be applied directly to unconsolidated 211u001ematerials. Instead, careful consideration of microstructure is necessary to adapt 211u001ethe methods successfully. Future work includes comparison of the measured 211u001evelocity values to additional theoretical estimates, investigation of Vp/Vs 211u001eratios and wave amplitudes, as well as modeling of dry and saturated sand-clay 211u001emixtures (e.g., Bonner et al., 1997, 1998). The results suggest that field data 211u001ecan be interpreted by comparing laboratory measurements of soil velocities to 211u001etheoretical estimates of velocities in order to establish a systematic method for 211u001epredicting velocities for a full range of sand-organic material mixtures at 211u001evarious pressures. Once the theoretical relationship is obtained, it can be used 211u001eto estimate the soil composition at various depths from field measurements of 211u001eseismic velocities. Additional refining of the method for relating velocities to 211u001esoil characteristics is useful for development inversion algorithms.