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

每年都有一些地震造成破坏，其中很大一部分是由于建筑物倒塌造成的，仅在美国每年造成的经济影响就高达约44亿美元。地震周期监测和地震预报是地质学研究的一个活跃主题，对于指导我们努力使社会及其基础设施为地震做好准备并减轻影响至关重要。目前还不可能对地震发生的时间和地点做出确定性预测。然而，可以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。这些统计估计的准确性在很大程度上取决于我们对特定断层系统的历史、其当前状态及其可能的演变的理解。这张图片是通过历史记录、地壳中应力积累的当前观察以及指导我们理解应力存储在哪里以及断层可能如何响应它们的模型生成的。尽管每个主要断层都有其独特的背景，但我们从对一个断层的详细研究中学到的东西会推动我们对更广泛过程的理解。断层的摩擦性质，以及这些性质在整个地震周期中的空间和时间变化，是了解其可能行为的关键参数。研究人员将利用夏威夷基拉韦厄火山南侧覆盖100年的现代和历史大地测量数据，并使用分析和数值模型来研究底层滑脱摩擦性质的时间演变及其与地震周期的关系。该项目的广泛影响包括危害、与美国地质勘探局的合作以及对本科生和研究生的支持。基拉韦厄的崩塌是该州自然灾害的主要来源，因为它会产生大地震，如2018年5月4日发生的Mw6.9 Leilani EStates地震，以及致命的海啸。了解其演化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。目前对基拉韦厄南侧的地质和地球物理观测的解释表明，连续蠕动、慢滑事件(SSE)和大地震都发生在同一断层面上，其中至少两个过程的组合同时运行。这些过程是如何联系和相互作用的，以及对楔形体及其地震周期的机制和演化的影响，是必须回答的基本问题，以提高我们对这些过程的理解。滑脱运动浅层的物理条件使基拉韦厄火山与大多数其他慢滑事件的汇聚边缘来源相比是一个极不寻常的异常值。此外，这里的SSE似乎发生在锁定带的上倾角，这是俯冲带中的大地测量基本上无法到达的区域。因此，这项研究提供了一个机会，通过将断层过程与其他地方的断层过程进行比较和对比来获得新的见解。对当前地表长期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了目前显示SSE的区域。这意味着目前活动的滑脱部分可以划分为四个不同的摩擦带，它们的摩擦性质跨越了速度减弱到速度加强的行为，并包括被认为支持SSE的过渡带(S)。这个项目表明，剥离上的摩擦力可以用速率和状态形式主义来描述。他们将对地震周期内不同时代的大地测量数据进行建模，以验证这一假设并回答以下问题：1)断层面流变学的参数范围如何充分预测观测到的长期蠕变速率、SSE和微震活动？2)这些参数是如何从1975年前的锁定状态演变到目前的？3)下裂谷带中的哪些岩浆超压与侧向形变率兼容？该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，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.