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

这个项目的主要目的是了解地震是如何沿着主要的走滑断层发生的，比如加州的圣安德烈亚斯断层。更具体地说，研究小组将确定构造板块的哪个部分是最强的，哪个是最弱的，这可以为走滑断层的力学提供更好的模型。为此，研究小组将研究北安那托利亚断裂带的部分地区，这是土耳其的一个走滑断层，其几何形状与圣安德烈亚斯非常相似，也是许多破坏性地震的发生地，如1999年的伊兹米特地震和d<s:1> cze地震以及2011年的Van地震。北安那托利亚断裂带有两个独特的属性，这使得它对了解地震周期和板块强度特别有用。首先，上地幔的小块岩石（这种岩石被称为捕虏体）沿着断层被火山带起。这些岩石可以直接评估地球如何？S地幔被认为是构造板块中最坚固的部分，它在走滑断层中变形。其次，整个中地壳板块——构造板块中另一个最坚固的部分——沿着北安那托利亚断层隆起。因此，在这个地区，研究小组可以直接测试走滑环境下构造板块不同部分的相对强度。该项目将通过培养美国研究生和促进国际科学合作来促进预期的社会成果。这个跨学科的项目将整合经验和理论方法，以产生对走滑断层系统岩石圈流变学的新认识。该项目的目的是通过综合实地调查、微观结构分析和地球动力学建模来研究土耳其的北安那托利亚断裂带。研究小组将利用北安那托利亚断裂带马尔马拉海地区的一系列独特暴露，更好地了解同一活动走滑断层的上地幔和中地壳的流变行为。首先，研究人员将研究沿断层系统北缘的两个火山中心暴露的一系列地幔捕虏体。捕虏体可表征地表以下45 ~ 80 km岩石圈地幔的力学性质和挥发性含量。其次，该团队将描述有限应变、应力、粘度和变形机制的横向变化，这些样品来自受北安那托利亚断裂带走滑变形影响的中地壳暴露，随后被挖掘出来。通过比较中地壳和上地幔的强度，将测试预测不同强度随深度变化的各种流变模型。地球动力学建模将模拟走滑系统地震周期中不同岩石圈层之间的相互作用，具体测试脆性断层和韧性层之间是否相互作用以控制整个岩石圈的应力水平。这些模型将根据从捕获体和中地壳暴露估计的应力和变形条件，以及1999年伊兹米特和d<s:1> cze地震前后的地表速度进行评估。通过将北安纳托利亚断裂带与其他走滑断裂系统的结果进行比较，本项目旨在总体上表征走滑系统的强度。特别是，它将解决走滑断层系统是否与其他构造环境中的断裂带具有系统不同的特征，以及脆层和韧性层之间的岩石圈反馈是否控制着走滑断裂带的力学行为。该项目的目标是准确了解活动走滑断层系统的地震周期，因此，这项工作与土耳其西部和其他地方的地震危险有关。

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.