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We present a broad view of present-day motions and deformations derived from uniform processing of GNSS observations within the Nubia-Arabia-Eurasia zone of plate interaction. The new observations we present provide a ~29% increase in the number of velocity determinations, a reduction in average station spacing from ~76 km to ~39 km, and an improvement in velocity uncertainties (for <1 mm/year), from 180 to 578 sites compared to our prior published solution (Reilinger et al., 2006). We use these new constraints to better evaluate the role of faults and blocks in controlling the character of continental deformation within the zone of plate interactions. Simple elastic block models show that internal deformation of the region occurs in large part on mapped, seismically active fault systems, indicating elastic behavior of the seismogenic crust (above ~15 km). For example, eastern central Anatolia, an area of > ~126,000 km², bounded by the North and East Anatolian Faults exhibits internal velocity differences of <0.5 mm/year, indicating strain rates of < ~1.5 nanostrain/year. Geodetically constrained fault slip rates obtained from this simplified approach are comparable to geologic rates, indicating that major faults have controlled the recent geologic evolution of the region (i.e. 5-10 Myr). The pattern of present-day deformation, including increasingly fast motions towards the Hellenic trench, and the roughly simultaneous opening of all the major Mediterranean basins in the early Miocene with the slowing of the Nubia-Eurasia convergence, support conceptual models that foundering and rollback of the subducted Nubian slab beneath the Aegean is the primary mechanism responsible for present-day motion and internal deformation of the Anatolian-Aegean region. [ABSTRACT FROM AUTHOR]

Since ~15 Ma, the active tectonics of Anatolia-Aegea (AN-AG) has resulted from the interaction between subduction of the African (AF) oceanic lithosphere along the Hellenic-Cyprus trench system, and continental collision between the Arabian (AR) and Eurasian (EUR) plates across the 600 km-wide, Turkish-Iranian deformation zone. Geologic, seismologic, and plate tectonic observations have provided important constraints on the evolution of AN-AG including the decoupling of AN-AG from EUR and AR with the development of the North and East Anatolian faults, and back-arc extension, and southward motion of western AN-AG. Furthermore, plate tectonic reconstructions, and geologic investigations of paleo-fault slip rates suggest relatively steady rates of motions for the AR and AF plates with respect to EUR, providing a roughly uniform temporal context in which to investigate relationships between plate interactions and lithospheric tectonics. Beginning in the late 1980s, geodetic observations, most notably GPS, have allowed highly precise quantification of the spatial and temporal behavior of presently active deformation within the zone of interaction of the AR-AF-EUR plate system. Quantification of motions provides a means to more precisely investigate the relationships between plate interactions and processes within the inter-plate deforming zone (in this case, AN-AG). Results immediately relevant to AN-AG kinematics and dynamics include: 1- AN-AG motion involves counterclockwise rotation with respect to EUR and AF, accommodating the NNW motion of AR, and SSW motion of the Hellenic Arc/Aegean Sea. Critically, the GPS observations demonstrate that rates of motion internal to Anatolia increase from east to west; an observation that provides evidence for Trench retreat being a driver of both SW translation of the Aegean micro plate, and N-S extension in western Anatolia; 2- known, active faults internal to AN-AG can account for > 70% of observed internal strains; 3- rates of strain accumulation on virtually all major faults are now known to 1-2 mm/yr providing important constraints on earthquake repeat times and hence seismic hazards; 4- geodetic motions agree within uncertainties with longer term geologic and plate tectonic rates in almost all cases (e.g., AR and Nubia motion with respect to Eurasia for > 10 Ma, Owens Fracture Zone, Dead Sea Fault, North and East Anatolian faults, Red Sea opening); 5- observations of pre-, co-, and 19 years post-seismic deformation for the 1999 M7.6 Izmit Earthquake continue to provide unique constraints on fault behavior through the full earthquake cycle.We will present a broad view of plate motions and deformations derived from 900 survey sites and 370 continuous GPS sites, including 600 sites in AN-AG, across the AR-AF-EUR plate system as "context" for understanding the transition from late stages of subduction to early continental collision, and how these interactions are accommodate by deformation of the AN-AG inter-plate zone. [ABSTRACT FROM AUTHOR]

The ~1500 km-long North Anatolian Fault (NAF) zone, the seismically and tectonically most important fault zone in Turkey, has generated nine major earthquakes in the 20th century. It splits into two main branches east of the Marmara Sea; the northern fault branch takes up most of the strike-slip component of Anatolia-Eurasia relative motion while the southern fault system accommodates the oblique extension of the Marmara basins. Based on > 20 years of GPS observations, direct constraints on strain accumulation within the Marmara Sea show that the Princes' Islands fault segment is accumulating strain at rates that are sufficient to produce a slip deficit since the last major earthquake in 1766 capable of generating a M>7 earthquake. In contrast, the offshore Central Marmara Fault (CMF), previously thought to represent the potential source for one or more M>7 earthquakes, shows no observable indication of accumulating strain. This is a challenging section to measure geodetically due to its distance from land but, if verified, the most likely explanation is that the fault is creeping aseismically to shallow levels. Creep on some segments of the NAF on land is known to occur as long-term post-seismic motion, affecting shallow parts of fault segments that slipped co-seismically, with the best observations coming from the 1999 M7.6 Izmit Earthquake. The low, or absence of, interseismic loading, along CMF, is puzzling. Possible explanations involve asymmetry in crustal elastic properties north and south of the fault, the southward dipping fault skewing the locus of surface shear strain to the south, creep at near plate velocity, or a very shallow locked zone (< 5 km). However, the depth distribution of microseismicity supports the notion that some shallow creep occurs in the western Marmara Sea from Ganos to the Central Basin (around the western part of CMF), arguing against shallow locking. Attempts continue to use in situ strategies to directly constrain fault slip rates; however neither the lengths of the possible creeping and locked segment nor the depth distribution of fault coupling are well constrained. Improvements in the classification of the geometrical and rheological features of the NAF in the Marmara could be realized by extending and densifying InSAR and GPS observations along the shores of the Sea and on the Princes' Islands, with direct implications for assessing the earthquake potential of the offshore fault systems in the Marmara Sea.In this study, we will present our strategies to estimate the variability of creep along NAF's branches in the Marmara Sea using the new spatially and temporally dense geodetic data sets. The results of this study will help constrain the mechanics of strain accumulation and release, and the development of extensional basins along strike-slip fault systems. [ABSTRACT FROM AUTHOR]