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A model of the vector motions of eight laser sites located in the western United States, Peru and Mexico has been developed from an analysis of 7 years of LAGEOS tracking data. This data represents the most comprehensive set of laser observations ever acquired on a near-earth satellite. Annual solutions of the global laser network from 1979 through 1985 have been used to determine the motion of the sites of interest with respect to the Minster and Jordan (1978) AMI-2 plate motion system. A new methodology has been implemented which has permitted a free least-squares adjustment for the vector motions of the sites with respect to an external reference frame developed from the observed motion of three of the strongest “base” tracking stations.

Of the laser sites for which vector motions are being determined, four are located in California; two stations are on the Pacific plate in southern California, and two northern California sites are on the North American plate. These California measurements are an augmentation to the NASA San Andreas Fault Experiment (SAFE), which has monitored baseline rates since 1972. East/west control to this network is provided by sites located in Colorado and Texas. The seventh station is located on the North American plate in Mexico. Finally, the South American laser station in Peru is included in the solution to enhance north/south control, thus completing the network.

A second technology based on radio astronomical techniques has provided observations of the motion of Very Long Baseline Interferometry (VLBI) antennas on the West Coast over this same time span. The VLBI model agrees quite well when compared with the motions observed from Satellite Laser Ranging (SLR), especially for the stronger SLR sites. Both models go far in explaining why the observed compression between Monument Peak and Quincy (the well-known “SAFE” baseline) is less (-2 to -3 cm/yr) than that expected from geological models (-5.3 cm/yr). Both VLBI and SLR models indicate that Quincy is not moving in its predicted AMI-2 southwest direction and that Monument Peak is moving at less than the full Pacific plate rate.

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