CAREER: Integration of rate-and-state friction and viscoelastic flow to model earthquake cycles on an oceanic transform fault

地震是威胁全世界社会的主要自然灾害。例如，加州南部的圣安德烈亚斯断层早就应该发生一场大地震，这场地震可能会影响南加州的2000多万居民。研究这些破坏性地震的一个基本挑战是，在给定的断层上，大地震之间的间隔很长。现代仪器只能捕捉到任何特定断层上地震周期的快照，过去地震行为的地质记录在估计震级和时间方面存在很大的不确定性。因此，使用这些有限的数据很难验证地震周期模型。 相比之下，海洋中的许多断层的重复间隔要短得多（约5年），并且与圣安德烈亚斯断层等大陆断层非常相似。这些大洋断裂上的重复地震周期被更好地记录下来。该项目将利用海洋转换断层作为研究地震物理的天然实验室。该项目将建立下一代地震模型，并将其应用于几个绘制良好的海洋转换断层。这些结果将提高我们对地震如何工作的理解，并将对圣安德烈亚斯断层的灾害评估产生影响。该项目将支持一名早期职业科学家和一名研究生。该项目还包括全面、综合的教育和外联活动，将使高中生和大学生以及公众受益。将通过一个公共软件库与科学界分享一套模拟转换断层上地震的软件包，海洋转换断层由于其系统性和可预测的地震行为，是研究地震周期的理想场所。本项目的研究目标是通过陆上和海上地震观测约束的数值模拟，了解海洋转换断层上大地震的基本时空关系。目前海洋转换地震周期的数值模型一般分为两类：（1）弹性层覆盖粘弹性层的模型，其中规定了同震滑动或应变软化来模拟地震;和（2）基于实验室推导的摩擦定律的动力学模型;例如，速率和状态摩擦，其中粘弹性流被忽略。该项目将首次将这两种模型结合起来，产生下一代地震周期的动力学模型。然后，该项目将把这一新模型应用于几个绘制良好的海洋转换断层，如Gofar/Discovery断层系统。这些模型将通过与教育计划的整合得到增强，该计划包括研究生，本科生和高中生解决问题和基于实验室的活动。研究结果将有助于更好地理解控制地震周期的关键参数和基本机制。目标是从概念上理解地震周期过渡到定量和预测地震行为的理解。

Earthquakes are a major natural hazard threatening society around the world. For example, the southern San Andreas Fault in California is long overdue for a major earthquake that could impact more than 20 million residents in Southern California. A fundamental challenge of studying these damaging earthquakes is the long interval between large events on a given fault. Modern instruments have only captured a snapshot of the earthquake cycle on any particular fault and geologic records of past seismic behavior suffer from large uncertainty in estimates of magnitude and timing. Thus, using these limited data makes it difficult to validate models of the earthquake cycle. In contrast, many faults in the ocean have a much shorter repeat interval (~5 years) and are good analogs to continental faults like the San Andreas Fault. The repeat earthquake cycle on these oceanic faults are much better recorded. This project will use oceanic transform faults as a natural lab to study earthquake physics. This project will build a next-generation earthquake model and apply it to several well-mapped oceanic transform faults. The results will improve our understanding of how earthquakes work and will have implications for hazard assessment of the San Andreas Fault. This project will support an early career scientist and a graduate student. This project also includes comprehensive, well-integrated education and outreach activities that will benefit high school and college students and the general public. A software package that simulates earthquakes on transform faults will be shared with the scientific community through a public software repository.Oceanic transform faults are an ideal place to study earthquake cycle because of their systematic and predictable seismic behavior. The research objective of this project is to understand the fundamental spatial-temporal relationship of large earthquakes on oceanic transform faults through numerical simulations constrained by onshore and offshore earthquake observations. The current numerical models of the ocean transform earthquake cycle generally fall into one of two categories: (1) models with an elastic layer overlying a viscoelastic layer where co-seismic slip is prescribed or strain softening is used to simulate earthquakes; and (2) dynamic models based on lab-derived friction law; e.g., the rate-and-state friction, where viscoelastic flow is ignored. This project for the first time will integrate these two kinds of models and produce a next-generation dynamic model of the earthquake cycle. The project will then apply this new model to several well-mapped oceanic transform faults, such as the Gofar/Discovery fault system. The models will be enhanced via integration with an education plan that incorporates graduate, undergraduate, and high school student problem-solving and lab-based activities. The results will lead to an improved understanding of the key parameters and fundamental mechanisms that control the earthquake cycle. The goal is to transition from a conceptual understanding of the earthquake cycle toward a quantitative and predictive understanding of earthquake behavior.