The Poisson ratio of the Australian crust: geological and geophysical implications

The Poisson ratio, which depends on the VP/VS ratio, provides much tighter constraints on the crustal composition than either the compressional or the shear velocity alone. The crustal Poisson ratio can be determined from the joint analysis of the travel times of waves converted at the Moho and of crustal multiples reflected at the top of the Moho. We have analyzed the records of the permanent stations installed on the Australian continent, complemented by the data of the SKIPPY experiment. The results reveal substantial variations in the Poisson ratio in the different tectonic units. For the Proterozoic crust, an increase of the Poisson ratio with increasing crustal thickness is systematically observed while for the Phanerozoic crust, the Poisson ratio tends to decrease for increasing crustal thicknesses. These observations are in remarkable agreement with the results of the deep seismic soundings that were performed in the former Soviet Union. The variations observed in the Proterozoic provinces can perhaps be explained by underplating of mafic materials at the base of the crust.