MEDICIONES GEODESICAS DE LARGAS DISTANCIAS: APLICACIÓN AL ESTUDIO DEL MOVIMIENTO DE PLACAS EN EL GOLFO DE CALIFORNIA

The modern geodetic methodologies such as electro-optic distance measurements and spatial positioning systems have increasing applications in geophysics to study tectonic deformations and relative plate motions.In this paper we show a rapid comparison of these geodetic methods in terms of applicability an precision.We discuss the methods of electronic distance measurements and of data processing in the case of large distances(about 90 km).Using these technics,a geodetic network of11 points and 150 km wide was measured in 1982 and 1986,across the CENTRAL Gulf of California.The comparison between 1982 and 1986 data allows us to estimate the relative displacements between Baja California and Sonora about 6-8  cm/yr;this value is consistent with previous estimations of plate motion between the Pacific and North American plates. Between Angel de la Guarda Island and Baja California a right lateral displacement of about 17 cm is observed in the four-years interval.In the southwestern part of the network, around the Sal-si puedes Channel, the deformation remains smaller than the estimated errors ,suggesting a locked segment of the plate boundary, coincident with the present seismic gap which is observed in this area. In the eastern part of the network, between the axial islands and the Sonoran coast, significant right lateral shear deformations occur with a relative displacement rate of 6 + 3 cm/yr. These results show that the strain accumulation is distributed in a large area around the plate boundary.