Investigation of the dynamic pressure surge effect in a fluid-filled fracture through numerical modeling and laboratory experiment

有充分的证据表明，自然发生的地震，即使是远在数千公里之外的地震，也能通过微弱的震动地震波触发其他地震。此外，地震波还能引起液化和火山喷发。然而，这些触发现象的物理原理尚不清楚。这项工作将侧重于了解可能引发地震的物理条件，无论是通过地震波传递还是人类活动，例如井中的流体注入。具体来说，本研究将探讨压力波动现象，这可能是所有这些触发现象的共同潜在机制，尽管在不同的地质环境中。研究者将使用数值模拟和物理实验来区分导致地震触发的相互竞争的物理机制。阐明触发机制对减轻自然灾害具有广泛和根本的社会影响。这项工作将支持一名早期职业教师和一名研究生。弱地震波的通过不仅会突然引发地震，还会改变水文系统的流体渗透性，引起液化并引发火山爆发。然而，究竟是什么机制控制了所有这些不同的触发事件在很大程度上是未知的，因为地震波引起的应力扰动非常小，大约只有几千帕斯卡，相当于几枚硬币的重量。寻找潜在的触发机制一直是地球物理学的中心问题。这项为期两年的研究试图在理解这些触发现象方面取得根本性的突破。研究人员最近发现了一种动态压力激增现象，在充满流体的裂缝中，流体压力相对于入射波压力会增加2-3个数量级。流体压力的增加可以降低有效围压，从而引发地震或产生压力梯度来驱动流体流动。这种新发现的效应在低频地震波中可能比高频地震波更为明显，这与观测结果一致。除了频率相关外，压力波动现象还与裂缝的几何形状和孔径有关。该项目将研究一个科学可验证的假设，它可以填补理解触发许多现象的知识空白，包括地震动力触发。为了验证这一假设，研究者将在数值模型和实验室实验中同时使用高性能计算。所提出的想法和方法是有希望的，并且可能对减轻地震和火山灾害产生深远的影响。此外，从该项目中获得的见解可用于创建新的地下传感和成像方法，有助于碳封存、核废料处理和非常规/地热能源开发。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。

It is well documented that naturally occurring earthquakes, even those located thousands of kilometers away, can dynamically trigger other earthquakes by the passage of a weak vibrating seismic wave. Furthermore, seismic waves can also induce liquefaction and volcanic eruptions. However, the physics of these triggered phenomena are unknown. This work will focus on understanding the physical conditions that can trigger earthquakes, either by passing seismic waves or by human activity, such as fluid injection at wells. Specifically, this study will investigate a pressure surge phenomenon, which could be the common underlying mechanism for all these triggered phenomena although in different geological settings. The investigator will use both numerical modeling and physical experiments to discriminate between competing physical mechanisms that lead to earthquake triggering. Elucidating the triggering mechanism has broad and fundamental societal impact in the mitigation of natural hazards. This work will support an early career faculty member and a graduate student. The passing of weak seismic waves not only can suddenly trigger earthquakes but can also change the fluid permeability of a hydrologic system, cause liquefaction and bring on volcanic eruptions. However, what mechanisms control all these different triggered occurrences are largely unknown because the stress perturbation due to the seismic wave is extremely small and it is on the order of a few thousand Pascal, equivalent to the weight of a few coins. Finding the underlying triggering mechanism has been a central problem in Geophysics. This 2-year study seeks to make a fundamental breakthrough in understanding these triggered phenomena. The investigator recently identified a dynamic pressure surge phenomenon where the fluid pressure in a fluid-filled fracture can increase 2-3 orders of magnitude relative to the incident wave pressure. The increase in fluid pressure can reduce the effective confining pressure to trigger earthquakes or to produce a pressure gradient to drive fluid flow. This newly discovered effect could be much more pronounced for a low-frequency incidence seismic wave than that for a high-frequency one, which agrees with observations. In addition to its frequency-dependence, the pressure surge phenomenon also depends on the fracture geometry and aperture. This project will investigate a scientifically testable hypothesis, which can fill the knowledge gap in understanding triggering of many phenomena, including earthquake dynamic triggering. To test this hypothesis, the investigator will use both high-performance computing on numerical models and laboratory experiments. The proposed idea and approaches are promising and may have far-reaching consequences in not only the earthquake but also the volcano hazards mitigation. In addition, the insights learned from this project can be used to create new subsurface sensing and imaging methods, useful in carbon sequestration, nuclear waste disposal, and unconventional/geothermal energy development.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.