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Abstract

The permanent rotation of the N.E.Pacific Rift is divided into three first-order rotations covering the whole rift between 20° and 60° N. during the last 80 mio years. The general movement of a clockwise rotation (35-40° altogether) was interrupted during the time between 40 and 20 m.y.b.p. by a weak counterclockwise one (8° altogether). These superordinate rotations can be subdivided in smaller ones with an average duration of 10 m.y. only. It is to suppose that all these rotations are a readjustment of the rift to a changed position of the spreading pole. Compared to it, short-time, oscillatory rotations represent compensating movements of the rift and stabilizing efforts of the plate. For the S.E.Pacific Rift it is supposed that the. Counterclockwise rotation taking place there for the last 7 m.y. is continuing, as may be concluded from the distribution of earthquake epicentres. Furthermore, the problems of pendulum movements and hinge zones at the S.E. and N.E.Pacific Rifts are discussed, which represent the magmatic activity of the rift. Hinge zones are lines of weakness of rifts, which can become fault zones. Up to now they were not mentioned in literature. The internal deformations of the Pacific Plate and Juan de Fuca Plate off California indicated by kinks of the rift, fault-folding and strike slip faults became intense about 1-2 m.y.b.p.