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During the past century, a series of predominantly westward migrating M>7 earthquakes broke an similar to 1000km section of the North Anatolian Fault (NAF). The only major remaining seismic gap along the fault is under the Sea of Marmara (Main Marmara Fault (MMF)). We use 20years of GPS observations to estimate strain accumulation on fault segments in the Marmara Sea seismic gap. We report the first direct observations of strain accumulation on the Princes' Islands segment of the MMF, constraining the slip deficit rate to 10-15mm/yr. In contrast, the central segment of the MMF that was thought to be the most likely location for the anticipated gap-filling earthquakes shows no evidence of strain accumulation, suggesting that fault motion is accommodated by fault creep. We conclude that the Princes' Islands segment is most likely to generate the next M>7 earthquake along the Sea of Marmara segment of the NAF.

We present evidence that GPS velocity estimates of plate motions and fault slip rates agree to within uncertainties with geologic estimates during the most recent phase of the geologic evolution of the E Mediterranean region (post-Late Miocene). On this basis, we use the GPS differential velocities to estimate the timing of initiation of the principal structures in NW Turkey, the N Aegean Sea, and central Greece, including, the Marmara Sea, the Gulfs of Evia (GoE) and Corinth (GoC). and the Kephalonia Transform fault (KTF). We interpret these ages to indicate that the North Anatolian fault propagated across the N Aegean, opening the GoE and GoC and initiating the KTF, during the past 1-4 Ma. We further suggest that Aegean extension that was earlier more distributed across the Aegean Basin became focused on this new fault system allowing the southern Aegean and Peloponnisos to translate SW with little internal deformation, as observed today with GPS. This change in tectonic configuration may account for the clear geologic evidence for crustal thinning throughout the S Aegean in apparent contradiction with low present-day strain rates. We further show that the low present-day strain rate along the southern edge of the Aegean micro-plate requires substantial aseismic slip along the plate interface below Crete, consistent with the low level of historic, subduction-type earthquakes along this segment of the subduction zone. (C) 2009 Elsevier B.V. All rights reserved.

Five years of continuously recording GPS observations in the Kingdom of Saudi Arabia together with new continuous and survey-mode GPS observations broadly distributed across the Arabian Peninsula provide the basis for substantially improved estimates of present-day motion and internal deformation of the Arabian plate. We derive the following relative, geodetic Euler vectors (latitude (degrees N), longitude (degrees E), rate (degrees/Myr, counterclock-wise)) for Arabia-Nubia (31.7 +/- 0.2, 24.6 +/- 0.3, 0.37 +/- 0.01), Arabia-Somalia (22.0 +/- 0.5, 26.2 +/- 0.5, 0.40 +/- 0.01), Arabia-India (18.0 +/- 3.8, 87.6 +/- 3.3, 0.07 +/- 0.01), Arabia-Sinai (35.7 +/- 0.8, 17.1 +/- 5.0, 0.15 +/- 0.04), and Arabia-Eurasia (27.5 +/- 0.1, 17.6 +/- 0.3, 0.404 +/- 0.004). We use these Euler vectors to estimate present-day stability of the Arabian plate, the rate and direction of extension across the Red Sea and Gulf of Aden, and slip rates along the southern Dead Sea fault south of the Lebanon restraining bend (4.5-4.7 +/- 0.2 mm/yr, left lateral; 0.8-1.1 +/- 0.3 mm/yr extension) and the Owens fracture zone (3.2-2.5 +/- 0.5 mm/yr, right lateral, increasing from north to south; 1-2 mm/yr extension). On a broad scale, the Arabian plate has no resolvable internal deformation (weighted root mean square of residual motions for Arabia equals 0.6 mm/yr), although there is marginally significant evidence for N-S shortening in the Palmyride Mountains, Syria at

We have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 Izmit and Duzce earthquake ruptures, using a three-dimensional viscoelastic finite element method. Our models confirm earlier findings that surface deformation within the first few months of the Izmit earthquake is principally due to stable frictional afterslip on and below the Izmit earthquake rupture. A second deformation process is required, however, to fit the surface deformation after several months. Viscoelastic relaxation of lower crust and/or upper mantle with a viscosity of the order of 2 to 5 x 10(19) Pa s improves the models' fit to later GPS site velocities. However, for a linear viscous rheology, this range of values is inconsistent with highly localized interseismic deformation around the North Anatolian Fault Zone (NAFZ) that was well observed prior to the earthquake sequence. The simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes, that is, that it has a power law or Burger's body (transient) rheology. A Burger's body rheology with two characteristic viscosities (2 to 5 x 10(19) Pa s and at least 2 x 10(20) Pa s) in the mantle is consistent with deformation around the NAFZ throughout the earthquake cycle.

We model the geodetically observed secular velocity field in north- western Turkey with a block model that accounts for recoverable elastic-strain ac- cumulation. The block model allows us to estimate internally consistent fault slip rates and locking depths. The northern strand of the North Anatolian fault zone (NAFZ) carries approximately four times as much right-lateral motion (24 mm/yr) as does the southern strand. In the Marmara Sea region, the data show strain accu- mulation to be highly localized. We find that a straight fault geometry with a shallow locking depth of 6-7 km fits the observed Global Positioning System velocities better than does a stepped fault geometry that follows the northern and eastern edges of the sea. This shallow locking depth suggests that the moment release associated with an earthquake on these faults should be smaller, by a factor of 2.3, than previously inferred assuming a locking depth of 15 km. Online material: an updated version of velocity-field data.