LISPB -- V. Studies of crustal shear waves

Many shots in the LISPB profiles produced shear waves with large amplitudes which were recorded by three-component stations. However, S waves seem to be strongly attenuated when they propagate through complex velocity structures. Upper crustal refractions (mainly land shots) and wide-angle reflections (mainly sea shots) were picked with the help of particle motion plots. S to P travel-time ratios (ts/tp) were used to calculate the distribution of Poisson's ratios in a crustal model. The results were generally close to σ= 0.25 except in the upper crust south of the Southern Uplands Fault (σ= 0.231) and in the middle crust under the Midland Valley (σ= 0.224).