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是破坏性地震的主因，比如2009年的拉奎拉6.3级地震和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，目前只是知之甚少，目前的余震和地震触发模型是不完整的。当前模型的缺陷在意大利中部尤为明显，在那里模型不能充分解释地震序列的时空特征。一个被提出的断层相互作用和地震聚集的机制是一些断层或断层的一部分滑动而不产生地面震动地震波。这种行为已经在圣安德烈亚斯断层、北安那托利亚断层和卡斯卡迪亚俯冲带以及世界上其他地方的部分地区得到了证实。对意大利中部微地震和断层岩石的研究间接支持这种慢震滑动假说，但在那里很难直接测量慢震断层滑动，因为需要专门的仪器来检测与此类事件相关的小振幅和慢速地面运动。我们的项目将在意大利中部浅层钻孔中部署一个多传感器仪器网络，该网络能够探测与缓慢地震断层滑动相关的小信号。我们收集的新数据将为控制地震和断层的机制提供有价值的新见解，对地震危害评估和地震和断层的物理学具有重要意义。我们部署的钻孔仪器将建立在国外对地球物理基础设施的重大投资基础上，以研究意大利地震断层系统，利用美国国家科学基金会地球范围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)地震断层对地震易发断层的应力是稳定的还是偶然的？(2)地震滑动模式是否与地震断层上或断层附近的微震活动模式相关？(3)地震断层滑动的时空特征是什么，包括滑动震级、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危险性的理解。我们收集的数据将为一项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，重点研究地震断层滑动和以意大利中部为自然实验室的地震。我们将培训一名美国研究生，学习钻孔应变仪分析方法。对意大利中部地震滑动的精确理解将对一个长期存在的争论产生影响，这个争论是关于自然界中低角度正断层滑动的可能性。来自钻孔网和其他地球物理网的数据将被纳入“海外无障碍地球研究”课程。AE总部位于意大利奥维托，靠近我们在意大利中部的现场。AE是一门为美国大学学生开设的顶级课程，它为残疾人提供了地质野外营地的替代方案，旨在通过让所有学生尽可能地接触地球科学，增加地球科学家的多样性。AE的学生将为一个重要的国际研究项目做出贡献。AE项目由独立资助，每年夏季无限期运行，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.