GPS determination of current Pacific-North American plate motion

Global Positioning System (GPS) data, collected by campaign-style GPS exper iments at five sites along the Gulf of California in 1996 and 1998, determi ne a locally based estimate for current relative motion between the Pacific and North American plates. At the mouth of the Gulf of California, the Pac ific plate moves 50.4 +/- 3.4 mm/yr, along an azimuth of N59.0 degrees W +/ - 2.7 degrees, relative to mainland Mexico. These estimates substantiate an d refine previous locally based GPS-determined rates, and agree with GPS de terminations of global plate motion. A reexamination of magnetic anomalies in the gulf used in the widely accepted NUVEL-1A global plate model has yie lded an average Pacific-North American relative velocity from 0.78 Ma to th e present of 51.1 +/- 2.5 mm/yr, The new GPS-determined velocity agrees wit h this estimate, supporting the ideas that the transfer of Baja California to the Pacific plate continued until ca, 1 Ma, and that the current Pacific -North American rate is greater than the 3.16 Ma average, The azimuth deter mination is similar to 5 degrees west of the NUVEL-1A results calculated fr om earthquake slip vectors and azimuths of gulf transforms offsetting both oceanic and continental crust, The Tamayo fracture represents the only faul t zone used in the NUVEL-1A model that offsets solely oceanic crust, This f ault zone trends N60 degrees W, consistent with the GPS-determined azimuth at the mouth of the gulf.