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Collaborative Research: The Mechanics of Intermediate Depth Earthquakes: a Multiscale Investigation Combining Seismological Analyses, Laboratory Experiments, and Numerical Modeling

合作研究：中深度地震的力学：结合地震分析、实验室实验和数值模拟的多尺度研究

基本信息

批准号：
1925920
负责人：
Yanbin Wang
金额：
$ 59.72万
依托单位：
University of Chicago
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-12-15 至 2024-11-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1925920&HistoricalAwards=false
关键词：
Collaborative Research Mechanics Intermediate Depth

项目摘要

It has been nearly a century since deep earthquakes, below about 50 kilometers, were definitively detected. Due to the difficulty observing such events, however, the mechanisms that control deep earthquakes are still poorly understood compared to shallower events. The pressures at depths greater than roughly 50 kilometers prohibit the frictional sliding and weakening mechanism that is essential to shallow events. This project focuses on the study of intermediate-depth earthquakes, those between approximately 50 and 300 km depth. The collaborative research combines small-scale scale laboratory experiments conducted at high pressure and temperature, seismological analysis of intermediate-depth earthquakes in well instrumented areas, and physics-based computer simulations to bridge the scales between the laboratory experiments and field observations. The hypothesis, generated from preliminary laboratory data, is that the minerals typical in subducting plates that produce deep earthquakes undergo one or more transformations that lead to mechanical instability as pressure and temperature increase. Minerals can densify when changing phase, reducing pressure locally and allowing for fracture propagation. Other reactions may create weak surfaces between or within grains. Under the right conditions, these instabilities can slip, generating heat and causing a runaway reaction leading to an earthquake. Laboratory data can reproduce these reactions at the small scale. Computer models will be created using the laboratory data to reproduce these experiments and determine parameters for the models. The results will then be systematically scaled up to simulate intermediate depth earthquakes in actual subduction zones. These large-scale simulations will be compared to the characteristics of observed earthquakes, with improved sensitivity to detect micro-earthquakes based on novel template matching and machine learning techniques. The combined research will help to demonstrate, for the first time, whether the same processes observed in small-scale laboratory specimens can account for large intermediate-depth earthquakes in subduction zones. Intermediate-depth earthquakes, while less common than shallow earthquakes, do result in casualties and significant damage. Understanding the mechanisms that cause such events will help to better characterize the potential hazard and risks to seismically active areas. The interdisciplinary experimental, numerical, and seismological work has the potential to transform our understanding of deep seismic events and deep Earth interior that are difficult to observe directly. The project will support postdoctoral researchers, graduate students, and undergraduate students further their education. It has been nearly a century since deep earthquakes, defined as below about 50 km depths, were first unequivocally discovered. The pressures at these depths preclude the frictional sliding that dominates shallow earthquakes and mechanisms of deep earthquakes remain poorly understood. Many challenges surround the study of deep earthquakes, including the inability to physically examine the fault structure and directly observe earthquake slip in the deep Earth interior. Here, this project investigate the mechanisms behind intermediate-depth earthquakes, defined as those between about 50 and 300 km depths, by integrating three key approaches: (1) detailed seismological investigation over a few well-studied tectonic settings, (2) controlled laboratory experiments on candidate mineral/rock groups with potential mechanical instabilities triggered by high-pressure, high-temperature reactions with acoustic emission monitoring and quantitative waveform analyses, and (3) micromechanics-based mathematical and physical models with a multiple scaling scheme to cover rupture processes from mm to km scales. Emerging new seismological tools such as template matching and machine learning allow detection of microevents in subduction zones with unprecedented spatial and amplitude resolution. The more than 10-fold increase in event detection provides much more illumination of fault areas than previously available. With such advances, this study will focus on the subduction zones in Central and Northern Japan, to examine event distribution, frequency magnitude statistics, aftershock productivities, source properties, fault orientation and stress drops. Experimentally, a number of major constituents of subducting slabs such as partially serpentinized olivine, eclogitization of lawsonite blueschist facies rocks, and even harzburgite, are now known to produce mechanical instability. Several physical mechanisms have been proposed for intermediate-depth earthquakes based on these observations. Development of experimental devices have increased sample linear dimensions by a factor of about 10. New developments in broadband acoustic emission technology have permitted quantitative analyses of acoustic emission events ("labquakes") using state-of-the-art seismological tools. Therefore, earthquakes and labquakes can be treated in a unified fashion in seismological analyses, allowing direct and better comparison with observations at very different scales. Thermo-poro-mechanical models will account for phase transformations, and formation of nano-shear or reaction bands as observed in the experiments. Simulations will be conducted in three stages: (1) Simulate the small-scale experiments. Detailed scans of experiments will allow us to mimic the perturbation in material that will initiate the transformation. The experiments at this stage will be used to validate and improve the model, as well as fit model parameters. (2) Mathematically upscale the model, homogenizing the small-scale behavior, so that the model can be used to simulate earthquakes in plates. (3) Simulate the Japan subduction zone. The models will then be compared with seismological observations to valid the results.The study will complete one of the last pieces in the puzzle of intermediate-depth earthquakes: verifying whether observed phenomena in small-scale experiments can quantitatively be the principal mechanism for regular intermediate-depth earthquakes observed at large depths. The combined seismological, experimental, and multiscale numerical work has the potential to truly transform the approach to the study of intermediate-depth earthquakes. The research will also lead to the development of new numerical methods and their application to geophysical processes.The subject of intermediate-depth earthquakes bears enormous societal impact with great scientific significance to the Earth and planetary science community. Large intermediate-depth earthquakes are capable of producing significant damage and casualties. Hence, an improved understanding of their mechanisms helps mitigate seismic hazard from these events. The mechanics of solids under high pressures is also of interest to physicists and material scientists. The interdisciplinary nature of the work has diverse applications throughout science and engineering.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.

近一个世纪以来，人们才真正探测到50公里以下的深层地震。然而，由于观测此类事件的困难，与浅层地震相比，控制深层地震的机制仍然知之甚少。深度大于大约50公里的压力阻止了摩擦滑动和减弱机制，而这对浅层事件至关重要。该项目侧重于研究中深度地震，即深度在50至300公里之间的地震。该合作研究结合了在高压和高温下进行的小规模实验室实验，在仪器完备的地区进行的中深度地震的地震学分析，以及基于物理的计算机模拟，以架起实验室实验和实地观测之间的桥梁。根据初步实验室数据得出的假设是，当压力和温度升高时，产生深层地震的俯冲板块中典型的矿物质会经历一次或多次转变，导致机械不稳定。当相变时，矿物可以致密化，从而降低局部压力并允许裂缝扩展。其他反应可能在颗粒之间或颗粒内部产生弱表面。在适当的条件下，这些不稳定性会发生滑动，产生热量并引起失控的反应，导致地震。实验室数据可以在小范围内重现这些反应。将利用实验室数据创建计算机模型来重现这些实验并确定模型的参数。然后，这些结果将被系统地放大，以模拟实际俯冲带的中深度地震。这些大规模模拟将与观测到的地震特征进行比较，并基于新的模板匹配和机器学习技术提高检测微地震的灵敏度。联合研究将有助于首次证明，在小规模实验室标本中观察到的相同过程是否可以解释俯冲带的大型中深度地震。中深度地震虽然不如浅层地震常见，但确实会造成人员伤亡和重大损失。了解导致此类事件的机制将有助于更好地描述地震活跃地区的潜在危害和风险。跨学科的实验、数值和地震学工作有可能改变我们对难以直接观测的深层地震事件和地球深部内部的理解。该项目将支持博士后研究人员、研究生和本科生继续深造。近一个世纪以来，深层地震（定义为深度低于50公里）首次被明确发现。这些深度的压力排除了主导浅层地震的摩擦滑动，而深层地震的机制仍然知之甚少。深层地震的研究面临着许多挑战，包括无法对断层结构进行物理检查和直接观察地球深处的地震滑动。在这里，该项目通过整合三种关键方法来研究中深度地震背后的机制，中深度地震被定义为深度在50到300公里之间的地震：(1)在一些研究充分的构造背景下进行详细的地震调查；(2)利用声发射监测和定量波形分析，对高压、高温反应引发潜在力学不稳定性的候选矿物/岩石群进行控制实验室实验；(3)基于微观力学的数学和物理模型，采用多种尺度方案，涵盖从毫米到公里尺度的破裂过程。新兴的地震工具，如模板匹配和机器学习，可以以前所未有的空间和振幅分辨率检测俯冲带的微事件。事件检测增加了10倍以上，提供了比以前更多的断层区域照明。有了这些进展，本研究将集中在日本中部和北部的俯冲带，研究事件分布、频率震级统计、余震生产力、震源性质、断层方向和应力降。实验表明，俯冲板块的一些主要成分，如部分蛇纹石化的橄榄石、长辉石蓝片岩相岩石的榴辉石化，甚至辉石，现在已知会产生机械不稳定性。基于这些观测，提出了几种中深度地震的物理机制。实验装置的发展使样品的线性尺寸增加了大约10倍。宽带声发射技术的新发展已经允许使用最先进的地震学工具对声发射事件（“labquakes”）进行定量分析。因此，地震和地震可以在地震学分析中以统一的方式处理，从而可以与非常不同尺度的观测结果进行直接和更好的比较。热孔力学模型将解释相变，以及实验中观察到的纳米剪切或反应带的形成。模拟将分三个阶段进行：(1)模拟小尺度实验。实验的详细扫描将使我们能够模拟材料中的扰动，从而启动转变。本阶段的实验将用于验证和改进模型，并拟合模型参数。(2)在数学上对模型进行了升级，均匀化了模型的小尺度行为，使模型可以用于模拟板块内地震。(3)模拟日本俯冲带。然后将这些模型与地震观测结果进行比较，以验证结果的有效性。这项研究将完成中深度地震的最后一块拼图：验证小规模实验中观测到的现象是否可以定量地成为大深度观测到的常规中深度地震的主要机制。地震学、实验和多尺度数值工作的结合有可能真正改变研究中深度地震的方法。这项研究还将导致新的数值方法的发展及其在地球物理过程中的应用。中深度地震的研究具有巨大的社会影响，对地球和行星科学界具有重要的科学意义。大的中深度地震能够造成重大的破坏和人员伤亡。因此，提高对其机制的理解有助于减轻这些事件的地震危害。固体在高压下的力学也是物理学家和材料科学家感兴趣的。这项工作的跨学科性质在整个科学和工程领域有不同的应用。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。