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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.

Abstract. Readjustment of the Krafla spreading segment on the Mid-Atlantic Ridge in Iceland, after a rifting episode from 1975 to 1984, is detected by radar interferometry. Crustal deformation from 1992 to 1995 is dominated by -24 mm/year subsidence above a shallow magma chamber at Krafla, superimposed on mm/year along-axis subsidence of the spreading segment relative to its flanks. The deformation is caused by cooling contraction at -3 km depth and ductile flow of material away from the spreading axis, at a rate decreasing with time.

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Satellite radar interferometry observations of the Reykjanes Peninsula oblique rift in southwest Iceland show that the Reykjanes central volcano subsided at an average rate of up to 13 millimeters per year from 1992 to 1995 in response to use of its geothermal field. Interferograms spanning up to 3.12 years also include signatures of plate spreading and indicate that the plate boundary is locked at a depth of about 5 kilometers. Below that depth, the plate movements are accommodated by continuous ductile deformation, which is not fully balanced by inflow of magma from depth, causing subsidence of the plate boundary of about 6.5 millimeters per year.