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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.

自从明确探测到约 50 公里以下的深部地震以来，已有近一个世纪的时间了。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。深度大于约 50 公里的压力抑制了浅层事件所必需的摩擦滑动和弱化机制。该项目重点研究中深度地震，即深度约 50 至 300 公里的地震。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、仪器仪表齐全地区中深度地震的地震学分析以及基于物理的计算机模拟，以在实验室实验和现场观测之间架起桥梁。根据初步实验室数据得出的假设是，产生深层地震的俯冲板块中的典型矿物会经历一种或多种转变，随着压力和温度的增加而导致机械不稳定。矿物在相变时会致密化，局部降低压力并允许裂缝扩展。其他反应可能会在颗粒之间或内部产生脆弱的表面。在适当的条件下，这些不稳定性可能会滑动，产生热量并引起失控反应，从而导致地震。实验室数据可以小规模重现这些反应。将使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，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的特征进行比较，并基于新颖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样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险和风险。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察的深层地震事件和地球深层内部的理解。该项目将支持博士后研究人员、研究生和本科生继续深造。自从首次明确发现深层地震（定义为深度约 50 公里以下）以来，已有近一个世纪的历史。这些深度的压力排除了在浅层地震中占主导地位的摩擦滑动，而对深层地震的机制仍然知之甚少。深部地震的研究面临许多挑战，包括无法物理检查断层结构并直接观察地球内部深处的地震滑移。在此，该项目通过整合三种关键方法来研究中深度地震（定义为深度约 50 至 300 公里之间的地震）背后的机制：（1）对一些经过充分研究的构造环境进行详细的地震学调查，（2）对候选矿物/岩石群进行受控实验室实验，这些矿物/岩石群具有由高压、高温反应和声发射监测引发的潜在机械不稳定性，以及定量波形分析；(3) 基于微力学的数学和物理模型，具有多种尺度方案，涵盖从毫米到公里尺度的破裂过程。模板匹配和机器学习等新兴地震学工具可以以前所未有的空间和振幅分辨率检测俯冲带中的微事件。事件检测量增加了 10 倍以上，为故障区域提供了比以前更多的照明。有了这些进展，这项研究将重点关注日本中部和北部的俯冲带，以研究事件分布、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，俯冲板片的许多主要成分，例如部分蛇纹石化橄榄石、硬钠长石蓝片岩相岩石的榴霞石化，甚至方辉橄榄岩，现在已知会产生机械不稳定性。根据这些观测结果，提出了中深度地震的几种物理机制。实验装置的开发使样本线性尺寸增加了约 10 倍。宽带声发射技术的新发展允许使用最先进的地震学工具对声发射事件（“实验室地震”）进行定量分析。因此，地震和实验室地震可以在地震学分析中以统一的方式处理，从而可以与不同尺度的观测结果进行直接和更好的比较。热孔机械模型将解释实验中观察到的相变以及纳米剪切或反应带的形成。模拟将分三个阶段进行：（1）模拟小规模实验。对实验的详细扫描将使我们能够模拟引发转变的材料扰动。此阶段的实验将用于验证和改进模型，以及拟合模型参数。 (2) 在数学上对模型进行升级，使小尺度行为均质化，以便该模型可以用于模拟板块中的地震。 (3)模拟日本俯冲带。然后将模型与地震观测进行比较，以验证结果。这项研究将完成中深度地震难题的最后一部分：验证小规模实验中观察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中深度地震的研究方法。这项研究还将促进新数值方法的发展及其在地球物理过程中的应用。中深度地震课题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。大型中深度地震能够造成重大破坏和人员伤亡。因此，更好地了解其机制有助于减轻这些事件的地震危害。高压下的固体力学也引起了物理学家和材料科学家的兴趣。这项工作的跨学科性质在整个科学和工程领域具有多种应用。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。