Present-day plate motions (original) (raw)

A data set. comprising 110 spreading rates, 78 transform fault azimuths and 142 earthquake slip vectors has been inverted to yield a new instantaneous plate motion model, designated RM2. The model represents a considerable improvement over our previous estimate RM1 (Minster, Jordan, Molnar and Haines, 1974). The mean averaging; interval for the relative motion data has been reduced to less than 3 My. A detailed comparison of RM2 with angular velocity vectors which best fit the data along individual plate boundaries indicates that RM2 performs close to optimally in most regions, with several notable exceptions. The model systematically misfits data along the India-Antarctica and Pacific-India ,plate boundaries. We hypothesize that these discre^panctes are manifestations of internal deformation within the Indian plate; the data are compatible with NW-SE compression across the Ninetyeast Ridge at a rate of about 1 cm/yr. RM2 also fails to satisfy the EW-trending transform fault azimuths observed in the FAMOUS area, which is shown to be a consequence of closure contraints about the Azores triple junction. Slow movement betwgen North and South America is required by the data set, although the angular velocity vector describing this motion remains poorly constrained. The existence of a Bering plate, postulated in our previous study, is not necessary if we accept the proposal of Engdahl and others that the Aleutian slip vector data are biased by slab effects. Absolute motion models are derived from several kinematical hypotheses and compared vitb the data from hotspot traces younger than 10 My. A-1though some of the models are inconsistent with the Wilson-biorgan hypothesis, the overall resolving power of the hotspot data is poor, and the directions of absolute motion for the several slower-moving plates are not usefully constrained. 2.