The earthquake cycle and the evolution of fault friction at Kilauea Volcano, Hawaii

每年都有许多地震造成破坏，其中大部分是由于建筑物倒塌，仅在美国，每年的经济影响就高达44亿美元左右。地震周期监测和地震预报是地质研究的一个活跃课题，对于指导我们为地震做好社会和基础设施的准备，以及减轻地震影响至关重要。目前还不可能对地震发生的时间和地点作出确定的预测。然而，对特定地区在特定时期内发生地震的可能性进行概率预测是可能的。这些统计估计的准确性在很大程度上依赖于我们对特定断层系统的历史、当前状态和可能演变的理解。这幅图是通过历史记录、当前对地壳中应力积累的观察和模型生成的，这些模型指导我们理解应力储存在哪里，以及断层可能如何对它们做出反应。尽管每个主要断层都有其独特的背景，但我们从详细研究一个断层中学到的东西，将推动我们对更广泛过程的理解。断层的摩擦特性，以及这些特性在整个地震周期中如何在空间和时间上变化，是理解其可能行为的关键参数。研究人员将利用来自夏威夷基拉韦厄火山南侧的丰富的现代和历史大地测量数据，覆盖100多年，并使用分析和数值模型来研究潜在滑脱的摩擦特性的时间演变及其与地震周期的关系。该项目的更广泛影响包括灾害、与美国地质勘探局的合作以及对本科生和研究生的支持。基拉韦厄火山的崩塌是该州自然灾害的主要来源，因为它会引发大地震，比如2018年5月4日发生的里氏6.9级的莱拉尼地震，以及致命的海啸。了解它的演变及其与遍布岛屿的灾难性滑坡特征的关系具有重要的社会意义。目前对基拉韦厄火山南侧的地质和地球物理观测结果的解释表明，连续的蠕变、慢滑事件（sse）和大地震都发生在同一断层面上，至少有两种过程同时发生。这些过程是如何联系和相互作用的，以及对楔体的力学和演化及其地震周期的影响，是必须回答的基本问题，以提高我们对这些过程的理解。与大多数其他缓滑事件的收敛边缘源相比，滑脱浅层的物理条件使基拉韦厄火山成为一个极不寻常的异常。此外，这里的sse似乎发生在闭锁带的上倾，这是一个在俯冲带基本上无法进行大地测量的区域。因此，这项研究提供了一个机会，通过与其他地方的断层过程进行比较和对比，获得新的见解。对当前长期地表位移的初步模拟表明，在这些运动中爬行的滑脱斑块勾勒出当前表现出sse的区域。这意味着滑脱层目前的活动部分可以被划分为四个不同的摩擦特性区域，这些摩擦特性跨越速度减弱到速度增强的行为，并包括被认为支持sse的过渡区。这个项目表明，在脱壳上的摩擦可以用速率和状态的形式来描述。他们将对地震周期内不同时期的大地测量数据进行建模，以检验这一假设，并回答以下问题：1)断层面流变学的参数范围能充分预测观测到的长期蠕变速率、sse和微震活动性？2)这些参数是如何从1975年之前的锁定状态演变到现在的？3)下裂谷带哪些岩浆超压与侧翼变形速率相容？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Every year a number of earthquakes cause devastation, much of it due to collapsing buildings, with economic impacts in the United States alone adding up to about $4.4 billion dollars a year. Earthquake cycle monitoring and earthquake forecasting is an active topic of geological research, and is crucial to guide our efforts to both prepare society and its infrastructure for earthquakes, and to also mitigate the impacts. It is not currently possible to make deterministic predictions of when and where earthquakes will happen. It is however, possible to make probabilistic forecasts about the likelihood of earthquakes happening in a specified area over a specified period. The accuracy of these statistical estimates is strongly dependent on our understanding of the history of a particular fault system, its current state, and its likely evolution. This picture is generated through historical records, current observations of the accumulation of stresses in the crust, and models that guide our understanding of where stresses are being stored and how a fault is likely to respond to them. Although each major fault has its own unique context, what we learn from studying one fault in detail moves our understanding of the broader processes forward. The frictional properties of a fault, and how these vary spatially and temporally throughout the earthquake cycle, are key parameters for understanding its likely behavior. The researchers will leverage the wealth of modern and historical geodetic data from the south flank of Kilauea Volcano, Hawaii, covering 100+ years, and use both analytical and numerical models to investigate the temporal evolution of the frictional properties of the underlying decollement and its relationship to the earthquake cycle. The Broader Impacts of this project span hazards, collaborations with the USGS and support for undergraduate and graduate students. Kilauea's decollement is a major source of natural hazards to the state, as it generates major earthquakes, like the May 4, 2018 Mw6.9 Leilani Estates earthquake, and also fatal tsunamis. Understanding its evolution and relationship to the catastrophic landslide features found throughout the islands is of great societal importance.Current interpretation of geological and geophysical observations from Kilauea's south flank suggests that continuous creep, slow slip events (SSEs), and major earthquakes are all occurring on the same fault plane, with combinations of at least two of these processes operating simultaneously. How these processes are connected and interact, and the implications for the mechanics and evolution of the wedge and its earthquake cycle, are fundamental questions that must be answered to improve our understanding of these processes. The physical conditions at the shallow depths of the decollement make Kilauea an extremely unusual outlier compared to most other convergent margin sources of slow slip events. In addition, the SSEs here appear to occur up-dip of the locked zone, a region largely inaccessible to geodetic measurements in subduction zones. This study, therefore, offers an opportunity to gain new insights through comparing and contrasting fault processes with those elsewhere. Preliminary modeling of the current secular surface displacements suggests that the patches of the decollement creeping in these motions outline the zones that currently exhibit SSEs. This implies the currently active portion of the decollement can be mapped into four distinct zones with frictional properties that span velocity-weakening to velocity-strengthening behavior and include the transitional zone(s) that are thought to support SSEs. This project suggests that friction on the decollement can be described using a rate-and-state formalism. They will model geodetic data from different eras within the earthquake cycle to test this hypothesis and answer the following questions: 1) What ranges of parameters for the fault plane rheology adequately predict the observed secular creep rates, SSEs, and microseismicity? 2) How have these parameters evolved from the locked state prior to 1975 through to current? 3) What magmatic overpressures in the lower rift zone are compatible with flank deformation rates?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.