The contribution of the IAG Intercommission Project WEGENER to TOPO-Europe

WEGENER is the acronym for Working group of European Geoscientists for the Establishment of Networks for Earth-science Research. At present it is established as the Inter-commission Project 3.2, between Commission 1 and Commission 3, of the International Association of Geodesy (IAG). The WEGENER Project, has promoted the development of scientific space-geodetic activities in the Mediterranean and European area for the last twenty years and has contributed to the establishment of geodetic networks designed particularly for Earth science research. The mission of WEGENER is the development of interdisciplinary work for the integration of space and terrestrial techniques in the study of the Eurasian/African plate boundary deformation zone and adjacent areas, including the establishment of an European velocity field, by promoting international cooperation and by being a Forum for European and other Earth-Scientists interested in the Eurasian/African plate boundary zone. WEGENER activities cover substantial parts of the scientific objectives of TOPO-Europe and WEGENER can contribute particularly in the anticipated monitoring of the 4-D evolution of the topography of the European continent and adjacent parts of North Africa, Asia and the Middle East by space geodetic and remote sensing techniques, in particular, by supporting the acquisition, processing and interpretation of satellite gravity and geodetic data, including exploitation of airborne multi-sensor data. TOPO-Europe involves very many geophysicists and geologists and it promotes modeling activities. These may perfectly be supported by the observational expertise of the geo-scientists of WEGENER. The amount and heterogeneity of the data to be expected from the TOPO-Europe program asks for dedicated data and product centers. One useful product that WEGENER, through its members, is already producing and which will be made available is a reliable and accurate vector velocity field map and a strain-map. Via the involvement of the GEODAC, the WEGENER GEOdynamic Data and Analysis Center, WEGENER will take care of a homogeneous and state-of-the-art GPS analysis. WEGENER will also address the important issue of the realization of an integrated multi-purpose network for the acquisition and availability of long-term, continuous, high-quality spatial and in situ measurements

GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions

The GPS-derived velocity field (1988-2005) for the zone of interaction of the Arabian, African (Nubian, Somalian), and Eurasian plates indicates counterclockwise rotation of a broad area of the Earth's surface including the Arabian plate, adjacent parts of the Zagros and central Iran, Turkey, and the Aegean/Peloponnesus relative to Eurasia at rates in the range of 20-30 mm/yr. This relatively rapid motion occurs within the framework of the slow-moving (∼5 mm/yr relative motions) Eurasian, Nubian, and Somalian plates. The circulatory pattern of motion increases in rate toward the Hellenic trench system. We develop an elastic block model to constrain present-day plate motions (relative Euler vectors), regional deformation within the interplate zone, and slip rates for major faults. Substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below ∼1-2 mm/yr, including central and eastern Anatolia (Turkey), the Southwestern Aegean/Peloponnesus, the Lesser Caucasus, and Central Iran. Geodetic slip rates for major block-bounding structures are mostly comparable to geologic rates estimated for the most recent geological period (∼3-5 Myr). We find that the convergence of Arabia with Eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the Caucasus and Zagros mountain belts around the periphery of the collision zone. In addition, we find that the principal boundary between the westerly moving Anatolian plate and Arabia (East Anatolian fault) is presently characterized by pure left-lateral strike slip with no fault-normal convergence. This implies that "extrusion" is not presently inducing westward motion of Anatolia. On the basis of the observed kinematics, we hypothesize that deformation in the Africa-Arabia-Eurasia collision zone is driven in large part by rollback of the subducting African lithosphere beneath the Hellenic and Cyprus trenches aided by slab pull on the southeastern side of the subducting Arabian plate along the Makran subduction zone. We further suggest that the separation of Arabia from Africa is a response to plate motions induced by active subduction

The protracted development of the continent–ocean transition in Afar

Continental breakup and the transition to seafloor spreading is characterized by extensional faulting, thinning of the lithosphere and, at magmatic margins, voluminous intrusive and extrusive magmatism1, 2, 3, 4. It is difficult to discriminate between different mechanisms of extension and magmatism at ancient continental margins because the continent–ocean transition is buried beneath thick layers of volcanic and sedimentary rocks5, 6 and the tectonic activity that characterized breakup has ceased. Instead, the timing of these mechanisms is inferred from theoretical models or from the geological record preserved at the fully developed, ancient rifted margins1, 5, 7, 8. Ongoing rifting in Ethiopia offers a unique opportunity to address these problems because it exposes subaerially the transition between continental rifting towards the south and seafloor spreading further northward. Here we synthesize constraints on the spatial and temporal evolution of magmatism and extension in Ethiopia. We show that although intrusion of magma maintains crustal thickness during the early stages of the continent–ocean transition, subsidence of the margin below sea level, and eruption of voluminous basalt flows, is initiated by late-stage thinning of the heavily intruded, weakened plate just before the onset of seafloor spreading. We thus conclude that faulting, stretching and magma intrusion are each important, but at different times during breakup

Review of GPS and Quaternary fault slip rates in the Himalaya-Tibet orogen

Previous studies related to the active deformation within the India-Asia collision zone have relied on slip rate data from major faults to test kinematic models for the region. However, estimated geodetic and Quaternary slip rates demonstrate large variability for many of the major faults in the region (e.g., Altyn Tagh and Karakorum faults). As a result, several studies have challenged the assumption that geodetic slip rates are representative of Quaternary slip rates. In this review, slip rate data from the Quaternary fault database for Central Asia are used to determine the overall relationship between Quaternary and Global Positioning System (GPS) slip rates for 19 faults. A least squares and Pearson correlation analysis are applied to investigate this relationship. To evaluate the sensitivity of the slip rate relationship to the presence/absence of individual faults and different Quaternary dating methods, the slip rates were systematically re-sampled. To account for the range of published uncertainties for slip rates, the Monte Carlo method was applied. Regression through 57 Quaternary/GPS slip rate pairs yields an r2 value of 0.71. Results from the re-sampling analysis show that the inclusion or exclusion of slip rate data from specific faults (e.g., the Ganzi fault, Karakorum fault, Himalayan Main Frontal thrust and Main Pamir thrust) have the highest influence on the strength of the correlation (changing the Pearson correlation coefficient by + 0.08, + 0.05, − 0.06, and + 0.06, respectively). Furthermore, there appears to be a systematic bias in the agreement between rates such that Quaternary rates tend to be higher than GPS rates. This bias is likely due to assumptions embedded in the geomorphic reconstructions of offset landforms used for estimating Quaternary slip rates in the dataset. Taken together, these results suggest that GPS slip rates are more likely to represent Quaternary slip rates when strict fault selection and geomorphic dating criteria are applied. Cases of inconsistencies in slip rates over different time scales may point to differences in the sensitivity of various fault slip measurement methods more often than secular rate changes