Higher, thicker landfills with steeper side slopes raise legitimate concerns about slope stability and liner integrity, particularly during earthquakes. The most important landfill properties for seismic safety are moduli and shear strength. The objective of this research is: a. to investigate techniques for characterization of landfills and other highly nonhomogeneous materials containing large aggregate; b. develop correlations between seismic velocity measurements and landfill shear strength measurements, and use these correlations to develop three- dimensional profile of shear strength variation within a landfill section; c. apply the methodology to one existing landfill.