We present and interpret Global Positioning System (GPS) measurements of crustal motions for the period 1988–1997 at 189 sites extending east‐west from the Caucasus mountains to the Adriatic Sea and north‐south from the southern edge of the Eurasian plate to the northern edge of the African plate. Sites on the northern Arabian platform move 18±2 mm/yr at N25°±5°W relative to Eurasia, less than the NUVEL‐1A circuit closure rate (25±1 mm/yr at N21°±7°W). Preliminary motion estimates (1994–1997) for stations located in Egypt on the northeastern part of Africa show northward motion at 5–6±2 mm/yr, also slower than NUVEL‐IA estimates (10±1 mm/yr at N2°±4°E). Eastern Turkey is characterized by distributed deformation, while central Turkey is characterized by coherent plate motion (internal deformation of <2 mm/yr) involving westward displacement and counterclockwise rotation of the Anatolian plate. The Anatolian plate is de‐coupled from Eurasia along the right‐lateral, strike‐slip North Anatolian fault (NAF). We derive a best fitting Euler vector for Anatolia‐Eurasia motion of 30.7°± 0.8°N, 32.6°± 0.4°E, 1.2°±0.1°/Myr. The Euler vector gives an upper bound for NAF slip rate of 24±1 mm/yr. We determine a preliminary GPS Arabia‐Anatolia Euler vector of 32.9°±1.2°N, 40.3°±1.1°E, 0.8°±0.2°/Myr and an upper bound on left‐lateral slip on the East Anatolian fault (EAF) of 9±1 mm/yr. The central and southern Aegean is characterized by coherent motion (internal deformation of <2 mm/yr) toward the SW at 30±1 mm/yr relative to Eurasia. Stations in the SE Aegean deviate significantly from the overall motion of the southern Aegean, showing increasing velocities toward the trench and reaching 10±1 mm/yr relative to the southern Aegean as a whole.

We use four geodetic satellite systems (Global Positioning System [GPS], European Remote Sensing [ERS], RADARSAT, and Satellite Pour l'Observation de la Terre [SPOT]) to measure the permanent deformation field produced by the İzmit earthquake of 17 August 1999. We emphasize measurements from interferometric analysis of synthetic aperture radar (SAR) images acquired by ERS and RADARSAT and their geodetic uncertainties. The primary seismological use of these data is to determine earthquake source parameters, such as the distribution of slip and the fault geometry. After accounting for one month's postseismic deformation, tropospheric delay, and orbital gradients, we use these data to estimate the distribution of slip at the time of the İzmit mainshock. The different data sets resolve different aspects of the distribution of slip at depth. Although these estimates agree to first order with those derived from surface faulting, teleseismic recordings, and strong motion, careful comparison reveals differences of 40% in seismic moment. We assume smooth parameterization for the fault geometry and a standard elastic dislocation model. The root mean square residual scatter is 25 mm and 11 mm for the ERS and RADARSAT range changes, respectively. Our estimate of the moment from a joint inversion of the four geodetic data sets is M 0 ‫ס‬ 1.84 ‫ן‬ 10 20 N m, a moment magnitude of M w 7.50. These values are lower than other estimates using more realistic layered earth models. Given the differences between the various models, we conclude that the real errors in the estimated slip distributions are at the level of 1 m. The prudent geophysical conclusion is that coseismic slip during the İzmit earthquake tapers gradually from approximately 2 m under the Hersek delta to 1 m at a point 10 km west of it. We infer that the Yalova segment west of the Hersek delta may remain capable of significant slip in a future earthquake.

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