We are using continuous and survey-mode Global Positioning System (GPS) and other relevant geological and geophysical information to clarify the special and temporal character of active deformation, and the forces driving this deformation, in the E. Mediterranean/Caucasus/Middle East region where the African, Arabian, and Eurasian plates interact. We place special emphasis on understanding the relationship between active deformation and geologic structures, and interactions between mantle dynamics and crustal tectonics. Our previous studies now provide an accurate (≤1mm/yr) description of regional deformation that is helping to define the basic principles that control continental deformation in this zone of plate interaction. These regional deformation patterns provide the framework for the more detailed studies we are now pursuing, including, (1) characterizing deformation (strain accumulation) along the main faults that control the large majority of deformation in this region (i.e., plate and block boundaries), (2) constraining better deformation in the S.E. Aegean (Greece and Turkey) that is closely related to active subduction and associated earthquake and tsunami hazards along the Hellenic trench, (3) quantifying deformation around unstable, continental triple junctions, including the Karliova and Karaman-Maras triple junctions in E Turkey, 4) determining the spatial character of strain accumulation as a function of the time in the earthquake cycle along the North Anatolian Fault, 5) monitoring and modeling postseismic deformation associated with the 1999, Izmit/Duzce earthquake sequence, and 6) working with collaborating partners to develop and apply realistic, dynamic models for active deformation of the continental lithosphere.
This project involves quantifying fault behavior (rates of strain accumulation and fault locking depths), and as such provides a physical basis for earthquake forecasting (estimates of earthquake repeat times, locations, and magnitudes) and hazard mitigation. We work closely with, and provide technology transfer (GPS, deformation modeling) to, academic and government scientific research institutions in Turkey, Greece, Armenia, Azerbaijan, Georgia, Russia, and Ukraine, including many international students who participate in all aspects of the research. The geodetic infrastructure we are developing in this region is being used to constrain GPS satellite orbits, thereby contributing to other GPS research studies (geodynamics, atmospheric water vapor, LIDAR, ionospheric studies).
This work is co-funded by the Geophysics and Tectonics Programs and the Office of International Science and Engineering.
This project has been focused on developing, in cooperation with 15 host-country partners, GPS observations of crustal motions in order to constrain plate and block motions and internal deformation in the complexly deforming region of the Arabia-Africa-Eurasia plate system (Figure 1). We have provided training in GPS surveying, geodesy, and/or geodynamic modeling, to host-country partner institutions (Armenia, Azerbaijan, Egypt, Eritrea, Ethiopia, Georgia, Greece, Kingdom of Saudi Arabia, Kuwait, Lebanon, Morocco, Russia, Turkey, Ukraine, Yemen) as well as USA and European partners from France and Spain. Our GPS velocity maps reveal large continental areas with low internal deformation in comparison to the rates of relative motion between adjacent areas (i.e., <10%). The majority of continental deformation is concentrated on the boundaries of these more coherent zones. This kinematic behavior is best quantified through block models, providing a link between regional, tectonic deformation and slip rates on faults, and as such the relationship between tectonics and earthquake processes and hazards. The direct estimates of slip rates and locking depths on active faults (e.g., Hellenic arc, North Anatolian, East Anatolian, Main Caucasus Thrust, Dead Sea, Main Recent, Tabriz, and many others), in combination with seismic observations (instrumental, historic, paleo-seismic), and neotectonic studies, allow quantitative estimates of earthquake hazards (potential magnitudes and probability of occurrence). Critical results from our studies include apparent a-seismic subduction along the Hellenic Arc off Crete (i.e., low strain accumulation on the subduction interface implies lower likelihood of great subduction earthquakes and associated tsunami), and identification of a strain anomaly near Baku, Azerbaijan and the major petroleum industry infrastructure on the Caspian Sea coast. Further studies are needed to better evaluate whether the anomaly is associated with a-seismic or seismic deformation. Observations of the earthquake deformation cycle from GPS and InSAR (Interferometric Synthetic Aperture Radar) observations of the 1999 Izmit/Duzce, Turkey earthquake sequence and other smaller, and less geodetically constrained events (e.g., Van, Turkey, 2011; Racha, Georgia, 1991) provide further constraints on the character of strain accumulation and release. In regard to global geodynamics, the relationship between present-day, geodetic motions and longer-term motion estimates from plate reconstructions and geologic observations has allowed us to identify both steady motions on the broadest scale that extend to >10 Myr for Nubia motion and > 20 Myr for AR plate motion. We have further identified changes in the character of deformation along the boundaries between Arabia, Africa (Nubia and Somalia), and the broad Eurasian boundary zone that correlate temporally with changes in relative plate motion. Because changes in plate motions require a change in the force balance on the plates, these changes provide information on the relative importance of different forces in driving plate motion, a long-standing question in Plate Tectonics. The temporal and spatial relationships we identified are most consistent with models where subduction is the dominant process driving plate motions and interplate deformation for the E Mediterranean plate system and possibly the entire system of plates converging with Eurasia along its southern boundary (Africa, Arabia, India, Australia).
