First epoch geodetic GPS measurements across the Afar Plate Boundary Zone



In November 1991, a geodetic network was installed across the actively rifting plate boundary zone between Africa and Arabia. Using the microwave signals transmitted by the satellites of the Global Positioning System (GPS), the relative positions of 37 stations are estimated with an average WRMS scatter of 12 or 14 mm for lines shorter or longer than 100 km, respectively. Assuming that the measurements can be repeated with the same precision in 1999, we expect to obtain horizontal uncertainties of 2.1 or 2.4 mm/yr in the rate of change in the short and long lines, respectively. This level of precision will tightly constrain geological models for the spatial distribution of deformation around the rift in Djibouti, and for the far-field plate motions surrounding the Afar depression.