Poisson's ratio is determined by two independent factors, i.e., the solid rock and dry or wet cracks. The former is influenced by the constituent mineral composition. The higher Poisson's ratio of the rock solid is, the higher is Poisson's ratio of the rock. Poisson's ratio of the solid rock may be roughly estimated from clay contents for clastic rocks. Cracks defined as flat pores of low aspect ratios lower in the dry case or heighten, in the wet case, Poisson's ratio of the rock. The magnitude of change depends on the volume concentration and aspect ratio of cracks. The higher the pore volume concentration and the lower the aspect ratio, the larger is the amount of change in Poisson's ratio. Cracks are also chiefly responsible for the difference between static and dynamic elastic constants and the ratio of static versus dynamic Poisson ratios approaches one when cracks occupy a smaller amount of the total volume.
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