Physical properties of rocks in the zone of transition from the Asian continent to the Pacific Ocean

Velocity-density relationships in the south of Sakhalin, Primor'ye, Chukotka, Kamchatka, and the south of the Greater Kuril island arc are based on Neogene - lower Paleozoic rock samples from the part of the crust accessible to drilling. The calculated densities differ in regions with a different type of development of the crust. A comparison of the possible nature of the stresses in the crust of such regions during post-Cretaceous time suggests a similiar pattern of evolution of the crust of Japan and the south of the Kuril arc. The increased densities in the lower part of the crust in Sakhalin and Japan could evidently serve as a source of energy for the completion of future folding of this region.

The disproportion of changes in the velocities of the P and S waves with change in pressure on the rock samples suggest the possibility of discriminating the predominant directions (horizontal or vertical) of past tectonic stresses. A study of the changes in velocities of the P and S waves in the tectonically weakened regions of the crust may provide information on the present stress state of the earth. —Author.