Collaborative Research: Subduction Megathrust Rheology: The Combined Roles of On- and Off-Fault Processes in Controlling Fault Slip Behavior

在过去的二十年里，在俯冲带中发现了广泛的断层滑动速度-从缓慢的构造速率蠕变到幕式震颤和滑动到快速地震-引发了一个新兴的新研究方向，专注于了解导致断层快速或缓慢滑动的物理机制，以及较慢的滑动如何可能与大型破坏性地震和海啸相互作用。为了提高我们对俯冲断层和地震力学的认识，需要对板块边界系统的变形行为进行定量和全面的研究。断层内的物质和周围围岩的变形已被证明是应力、温度、应变率和岩石类型的函数。与此同时，由于岩石类型和断层沿着条件的变化，断层带的不均匀性已经成为解释慢地震和慢滑动事件发生的主要假设。因此，量化俯冲带岩石的变形行为一直是实验学家不断努力的奋进。通过实验和数值模型，本研究将具体解决两个问题。首先，大逆冲断层的流变学沿着及其不均匀性如何影响断层滑动行为？断层内外的非弹性变形如何影响应变能的积累以及锁滑的发生和分布？新的实验将在俯冲带岩石上进行，这些岩石在地震开始的深度处的压力和温度下变形。实验数据将告知数值模型，该模型可以桥接尺度以包括沿断层沿着的不均匀性。这项工作的净结果将是新的定量见解的空间异质性和流变学的作用，在俯冲系统在一系列的时间尺度。该项目将支持早期职业科学家的培训，包括本科生和研究生，博士后和两名早期职业PI。此外，该项目将利用新开发的代码开发俯冲带流变学建模短期课程。短期课程的课程将以一套短视频的形式公开提供，其中包括使用代码作为最大化其可访问性的途径的说明。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Over the past two decades, the discovery of a broad spectrum of fault slip speeds in subduction zones – from slow tectonic rate creep to episodic tremor and slip to fast earthquakes - has ignited a burgeoning new research direction focused on understanding the physical mechanisms that cause faults to slip fast or slow, and how slower slip might potentially interact with large destructive earthquakes and tsunamis. Advancing our knowledge of subduction fault and earthquake mechanics requires a quantitative and holistic investigation of the deformation behavior of the plate boundary system. The deformation of both material within the fault and the surrounding wall rocks has been shown to be a function of stress, temperature, strain rate, and rock type. At the same time, heterogeneity in the fault zone, due to variations in rock type and conditions along the fault, has emerged as a leading hypothesis to explain the occurrence of slow earthquakes and slow slip events. Therefore, quantifying the deformation behavior of subduction zone rocks has been a growing endeavor for experimentalists.Through experiments and numerical models, this research will specifically address two questions. First, how does rheology along the megathrust - and its heterogeneity - affect fault slip behavior? Second, how does inelastic deformation on- and off-fault affect strain energy accumulation and the occurrence and distribution of locking and slip? New experiments will be conducted on subduction zone rocks that are deformed under pressures and temperatures present at the depths where earthquakes begin. The experimental data will inform numerical models that can bridge scales to include heterogeneity along the fault. The net result of this work will be new quantitative insights into the roles of spatial heterogeneity and rheology in subduction systems over a range of timescales. The project will support training of early career scientists including undergraduate and graduate students, postdocs, and two early career PIs. In addition, the project will develop a modeling short course for subduction zone rheology using newly developed codes. The lessons from the short course will be made publicly available as a set of short videos that include instructions for using the codes as a pathway to maximize their accessibility.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.