Measuring aseismic fault slip during a normal faulting earthquake sequence in central Italy

意大利中部的构造断层系统导致了显著的破坏性地震--如2009年的6.3级L和2016年的阿马特里切6.2级地震--以及可能持续数月甚至数年的复杂地震序列。控制地震空间和时间聚集的过程，如意大利中部序列的情况，目前只被很少了解，目前关于余震和地震触发的模型也不完整。目前模型的缺点在意大利中部尤其明显，那里的模型不能充分解释地震序列的空间和时间特征。一种提出的断层相互作用和地震聚集的机制是，一些断层或部分断层滑动而不产生地面震动地震波。在圣安德烈亚斯断层、北安纳托利亚断层和卡斯卡迪亚俯冲带等世界各地的部分地区也出现了这种行为。对意大利中部微震和断层岩的研究间接支持了这一缓慢的无地震滑动假说，但在那里很难直接测量缓慢的无地震断层滑动，因为需要专门的仪器来检测与此类事件相关的小幅度和慢速度的地面运动。我们的项目将在浅井中部署一个多传感器仪器网络，能够探测与意大利中部缓慢的无地震断层滑动有关的小信号。我们收集的新数据将为控制地震和断层作用的机制提供有价值的新见解，对地震危险性评估和地震和断层作用的物理学具有重要影响。我们部署的钻孔仪器将建立在大量外国对地球物理基础设施的投资基础上，以研究意大利的无地震断层系统，利用来自NSF地球示波器板块边界观测站的剩余仪器。由此产生的数据集将解决几个一阶问题：(1)无震断层在地震多发断层上加载应力是稳定的还是周期性的？(2)无震滑动的模式是否与无地震断层上或附近的微震活动模式相关？(3)无震断层滑动的空间和时间特征是什么，包括滑动幅度、滑动速率、传播方向和速率以及事件持续时间？这些问题直接关系到我们对断层摩擦和力学以及地震灾害的理解。我们收集的数据将为一个新兴的国际合作提供支持，该合作涉及美国研究人员和学生，他们专注于无地震断层滑动和地震，将意大利中部作为一个天然实验室。我们将培训一名美国研究生学习钻孔应变仪分析方法。对意大利中部地区无地震滑动的精确理解将关系到关于自然界中低角度正断层上滑动的可能性的长期争论。来自钻孔网络和其他地球物理网络的数据将被纳入无障碍海外地球研究(AE)课程。AE的总部设在意大利的奥维埃托，靠近我们意大利中部的现场。AE是为美国大学学生开设的顶峰课程，为残疾人士提供地质野外训练营的替代方案，旨在通过让所有学生尽可能地接触到地球科学来增加地球科学家的多样性。AE专业的学生将为一个重要的国际研究项目做出贡献。AE计划是独立资助的，将在每年夏天无限期地运行，每年为大约8-12名美国学生提供服务，包括残疾学生。该奖项由国际科学与工程办公室共同资助。

The tectonic fault system in central Italy is responsible for notably destructive earthquakes -such as the M6.3 2009 L'Aquila and M6.2 2016 Amatrice events- and complex earthquake sequences that may last for several months or even years. The processes that control the spatial and temporal clustering of earthquakes, as in the case of the central Italy sequences, are currently only poorly understood and current models for aftershocks and earthquake triggering are incomplete. The shortcomings of current models are particularly true for central Italy, where the models inadequately explain the spatial and temporal characteristics of earthquake sequences. One proposed mechanism for fault interaction and earthquake clustering is that some faults or portions of faults slip without producing ground shaking seismic waves. Such behavior has been suggested on portions of the San Andreas fault, the North Anatolia fault, and the Cascadia subduction zone among other locations around the world. Studies of micro-earthquakes and fault rocks in central Italy indirectly support this slow aseismic slip hypothesis, but direct measurement of slow aseismic fault slip has been difficult obtain there, because specialized instrumentation is required to detect the small amplitude and slow speeds of ground motions associated with such events. Our project will deploy a network of multi-sensor instruments in shallow boreholes capable of detecting the small signals associated with slow aseismic fault slip in central Italy. The new data that we collect will provide valuable new insights into the mechanisms that control earthquakes and faulting, with important implications for earthquake hazards assessment and the physics of earthquakes and faulting. The borehole instruments that we deploy will build on significant foreign investments in geophysical infrastructure to study aseismic Italy fault systems, taking advantage of surplus instrumentation from the NSF EarthScope Plate Boundary Observatory. The resulting data sets will address several first order questions: (1) Do aseismic faults load stress on earthquake prone faults steadily or episodically through time? (2) Does the pattern of aseismic slip correlate with the pattern of micro-seismicity on or near aseismic faults? (3) What are the spatial and temporal characteristics of aseismic fault slip, including slip magnitudes, rates, propagation directions and rates, and event durations? These questions bear directly on our understanding of fault friction and mechanics, and earthquake hazards. The data we collect will feed a burgeoning international collaboration involving US researchers and students focused on aseismic fault slip and earthquakes using central Italy as a natural laboratory. We will train a US graduate student in borehole strainmeter analysis methods. Refined understanding of aseismic slip in central Italy will bear on a long-standing debate regarding the possibility of slip on low angle normal faults in nature. Data from the borehole network and other geophysical networks will be incorporated into the Accessible Earth Study Abroad (AE) curriculum. AE is based in Orvieto, Italy, near our field central Italian field site. AE is a capstone course for students at US universities that provides a disability-accessible alternative to geology field camp and aims to increase diversity among geoscientists by making geoscience as accessible as possible to all students. Students of AE will contribute to a major international research program. The AE Program is funded independently and will run every summer indefinitely, serving approximately 8-12 US students each year, including students with disabilities. This award is cofunded by the Office of International Science and Engineering.