Determination of the elastic properties of earth materials by laboratory means is subject to sizable errors. These errors may be serious in spite of the large safety factors normally used in engineering design, particularly if the structure must withstand severe dynamic loads. Means of obtaining elastic constants “in‐situ” are described. Further, the phenomenon of displacement multiplication between the underlying competent rock and overlying alluvium or fill is reviewed and the first instrumentation system designed specifically to measure this relationship for engineering purposes is described.