Collaborative Research: Evaluating the Rheological Structure of the North Anatolian Fault Zone, Turkey

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The main objective of this project is to understand how earthquakes occur along major strike-slip faults, such as the San Andreas fault in California. More specifically, the research team will identify which part of the tectonic plates are the strongest and which ones are the weakest, which can feed into better models of the mechanics of strike-slip faults. To do this, the team will study parts of the North Anatolian Fault zone, a strike-slip fault in Turkey with a geometry very similar to the San Andreas and the site of many destructive earthquakes, such as the 1999 Izmit and Dücze earthquakes and the 2011 Van earthquake. There are two unique attributes of the North Anatolian Fault zone that make it particularly useful for understanding the earthquake cycle and the strength of the plate. First, small pieces of the upper mantle (such rocks are known as xenoliths) are brought up in volcanoes along the fault. These rocks allow for direct evaluation of how the Earth?s mantle, which is thought to be the strongest part of a tectonic plate, is deformed in a strike-slip fault. Second, entire blocks of the middle crust, the other candidate for the strongest part of a tectonic plate, have been brought up along the North Anatolian Fault. Thus, in this region, the team can directly test the relative strengths of the different parts of the tectonic plates in a strike-slip setting. The project will advance desired societal outcomes through training of U.S. graduate students and promote international scientific collaboration. This interdisciplinary project will integrate empirical and theoretical approaches to generate new understanding of lithospheric rheology in strike-slip fault systems. The aim of the project is to study the North Anatolian Fault zone, Turkey, by integrating field investigations, microstructural analysis, and geodynamic modeling. The research team will use a series of unique exposures in the Sea of Marmara region of the North Anatolian Fault zone, to better understand the rheological behavior of the upper mantle and middle crust in the same, active strike-slip fault. First, the researchers will study a series of mantle xenoliths exposed in two volcanic centers along the north margin of the fault system. The mechanical properties, and volatile content of the lithospheric mantle at 45 to 80 km below the surface will be characterized from the xenoliths. Second, the team will characterize lateral variations in finite strain, stress, viscosity, and deformation mechanisms of samples from a mid-crustal exposure that was affected by strike-slip deformation in the North Anatolian Fault zone and was subsequently exhumed. Various rheological models that predict different strength variations with depth will be tested by comparing the mid-crustal to the upper mantle strength. Geodynamic modeling will simulate how the different lithospheric layers interact during the seismic cycle in strike-slip systems, testing specifically whether the brittle fault and ductile layers interact to control the stress level throughout the lithosphere. These models will be evaluated against the stress and deformation conditions estimated from xenoliths and mid-crustal exposures, as well as surface velocities before and after the 1999 Izmit and Dücze earthquakes. By comparing the North Anatolian Fault zone with results from other strike-slip fault systems, this project aims at characterizing the strength of strike-slip systems in general. In particular, it will address if strike-slip fault systems have systematically different characteristics than fault zones in other tectonic environments, and whether a lithosphere feedback between brittle and ductile layers controls the mechanical behavior of strike-slip fault zones. The goal of the project is to produce an accurate understanding of the seismic cycle on active strike-slip fault systems, and hence, the work is relevant to seismic hazards in western Turkey and elsewhere.