On the spreading of the East Pacific Rise

We analyze through statistical methods the mechanics of the East Pacific Rise by considering the relative angular velocities of spreading of the Pacific-Nazca, Pacifie-Cocos and Pacific-Rivera margins. We focus our attention on verifying the validity of some issues such as the constancy of the velocity of spreading, the symmetry of the spreading and the "rigid" rotational behaviour of the plates. Our findings can be summarized in the following four points: 1. (a) the relative velocities of all considered margins decreased in modulus around 1.5 m.y. ago; 2. (b) the spreading is asymmetric and the pattern is in general agreement with the model of Stein et al. (1977); 3. (c) the Pacifie-Cocos and the Pacific-Nazca margins are migrating respectively eastward and westward; 4. (d) statistical evidence suggests that a "rigid" rotational behaviour is not always verified. © 1990.