GLEAftiMßriOUSE FOR FCOERAl SCIENTIFIC AND TtCKN^AL mf' ^ATiON CFSTI DOCUMENT MANAGEMENT BRANCH 410.ii LIMITATIONS IN KEPRQDUCTiON QUALITY

High-frequency geometric ray theory i8 used to investigate the refracted arrival from a high-speed layer embedded in an infinite medium. The effect of changing the layer thickness to dominant wavelength ratio (E/ ^ ) and the range io depth ratio ( p/H) is analyzed for a point oempressional source. The results approximate the exact solution when E/Väsf . The theory predicts shingling and shows that it is distance-limited. The maximum ( distance at whioh shingling is observed decreases as E/A^ decreases. Beyond a certain minimum distance, the refracted arrival consists of a superposition of waves whose phase velocities approach the compressional velocity in the layer at large distances. These waves include the reflected waves which cross the layer at least once in the compressional mode and the head waves which are generated by reflected waves which do not cross the layer in the compressional mode. There are nm-C )!/!. reflected ray paths which cross the layer Ti times in the compressional mode and m times in the shear mcde which arrive at exactly the same time. A formula is derived which expresses the composite amplitude of these rays in the form of a series which .^