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

该项目的主要目标是了解地震是如何沿着主要的走滑断层发生的，例如加州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一部分是最强的，哪一部分是最弱的，这可以为更好的走滑断层力学模型提供信息。为此，该团队将研究北安纳托利亚断层带的部分区域，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年的伊兹米特和杜切地震以及2011年的货车地震。北安纳托利亚断层带有两个独特的属性，这使得它对理解地震周期和板块强度特别有用。首先，上地幔的小块（这种岩石被称为捕虏体）被带出沿着断层的火山。这些岩石可以直接评估地球如何？被认为是构造板块最坚固部分的地幔在走滑断层中变形。第二，整个中地壳块体，构造板块最强部分的另一个候选者，已经沿着北安纳托利亚断层被带了上来。因此，在这一地区，研究小组可以直接测试走滑构造板块不同部分的相对强度。该项目将通过培训美国研究生和促进国际科学合作来推动预期的社会成果。这个跨学科的项目将整合经验和理论的方法，以产生在走滑断层系统的岩石圈流变学的新认识。该项目的目的是研究土耳其北安纳托利亚断层带，通过整合实地调查，微结构分析和地球动力学建模。研究小组将利用北安纳托利亚断层带马尔马拉海地区的一系列独特的暴露，以更好地了解上地幔和中地壳在同一活跃的走滑断层中的流变行为。首先，研究人员将研究一系列地幔捕虏体，这些捕虏体沿着断层系统北缘的两个火山中心出露。岩石圈地幔的力学性质和挥发分含量在地表以下45至80公里的特点是从捕虏体。其次，该小组将表征有限应变，应力，粘度和变形机制的样品中地壳暴露的横向变化，受到北安纳托利亚断层带走滑变形的影响，随后被挖出。将通过比较中地壳与上地幔的强度来检验预测不同强度随深度变化的各种流变模型。地球动力学模型将模拟不同的岩石圈层如何在地震周期中在走滑系统中相互作用，特别是测试脆性断层和韧性层是否相互作用以控制整个岩石圈的应力水平。将根据捕虏体和中地壳暴露估计的应力和变形条件以及1999年伊兹米特和杜策地震前后的表面速度来评估这些模型。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，本项目旨在从总体上表征走滑系统的强度。特别是，它将解决，如果走滑断层系统有系统的不同特征比其他构造环境中的断层带，以及是否岩石圈之间的反馈脆性和韧性层控制走滑断层带的力学行为。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灾害有关。

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.