Seismic imaging based on numerical simulations of seismic waves: from global to hydrocarbon-reservoir applications

了解地球的地质演化一直是激发人类好奇心的基本科学问题之一。过去是什么样的构造过程和地质事件塑造了地球表面观测到的地形、地质和构造特征，是什么样的内部动力学过程驱动了复杂的构造板块运动，这些板块运动和构造应力是如何引起地震的？这些有趣的问题一直是固体地球物理研究的中心，其中地震学在阐明地球内部方面发挥着主导作用，并为破译我们星球的过去，现在和未来提供了重要线索。另一方面，地震学致力于了解地震这一对人类破坏最大的自然灾害之一，包括地震的位置、震源机制、地震波传播和诱发地面震动的强度。地震目录的收集和对异质内部结构影响的更好了解为我们提供了长期地震危险评估和风险缓解的重要指导。多伦多大学的计算地震学小组参与了地震学研究，寻求上述问题和主题的答案和解决方案。特别是，我们开发和应用维护良好的社区谱元素软件包，准确地模拟地震波在2D/3D非均匀介质中的传播。为了理解与俯冲带、大陆碰撞带、俯冲带等有关的构造过程，我们使用来自地震阵列记录的独特数据集，包括区域地震数据、噪声互相关函数（NCF）和地震接收器函数（RF，即，转换/散射/尾波的主要阶段），结合伴随层析成像技术，以揭示详细的结构下的地震阵列以及在大陆和全球规模。地震学方法的进步也为应用地球物理应用带来了新的见解，特别是石油和天然气勘探和开采的地震成像和微震监测。例如，伴随水力压裂过程的微震事件可以通过波形建模、源反演以及层析成像更准确地定位、监测和解释，在水力压裂过程中，流体和支撑剂在高压下注入相对不可渗透的烃储层中以产生用于气体或/和油被有效排出的路径。我们应用波传播的全数值模拟来模拟复杂地质结构中的微震事件，并采用创新的地震反演方法来绘制采矿和水力压裂应用的详细地下非均质性。通过以前的NSERC（个人）发现补助金和其他资金来源的支持，我能够建立一个充满活力的研究小组，由2名博士后，8名研究生（包括3名已完成的硕士）组成。加入多伦多大学五年来，共完成本科生论文7篇（其中B.Sc.论文2篇）。在同一时期，我们的团队在同行评审期刊上发表了13篇论文（另外1篇被接受，2篇正在审查）。我们还共同撰写了一本书的章节和2个会议论文集的扩展摘要。我和我的博士后、研究生们还做了50多个会议和研讨会报告。我们的研究团队希望在未来五年内保持类似的团队规模、HQP培训计划和生产力水平。

Understanding the geological evolution of the planet Earth has been one of the fundamental scientific questions that pique human curiosity. What are the tectonic processes and geological events in the past that shaped the topographic, geological and tectonic features observed on the Earth’s surface, what are the internal dynamical processes that drive the complex tectonic plate motions, and how do these plate motions and tectonic stress cause earthquakes? These intriguing questions have been the centre of solid geophysical research, in which seismology plays a leading role in illuminating the Earth’s interior and presents important clues to decipher the past, present and future of our planet. On another front, seismology engages in understanding earthquakes, one of the most damaging natural disasters to mankind, including their locations, source mechanisms, seismic wave propagation and the intensity of induced ground shaking. The collection of seismic catalogues and better understanding of the effect of heterogeneous internal structures provide us crucial guidance on long-term seismic hazard assessment and risk mitigation. The computational seismology group at University of Toronto is involved in seismological research that seeks answers and solutions to the above questions and subjects. In particular, we develop and apply well-maintained community spectral-element software packages that accurately simulate the propagation of seismic waves in 2D/3D heterogeneous media. In an effort to understand the tectonic processes associated with subduction zones, continental collision zones, cratons, etc., we use unique datasets from seismic array recordings, including regional earthquake data, noise cross-correlation functions (NCF), and teleseismic receiver functions (RF, i.e., converted/scattered/coda waves of teleseismic main phases), in combination with adjoint tomographic techniques to reveal detailed structures beneath seismic arrays as well as at continental and global scales. The methodology advancement in earthquake seismology also brings new insight into applied geophysical applications, in particular seismic imaging and microseismic monitoring for oil and gas exploration and mining. For example, microseismic events accompanying hydraulic fracturing processes in which fluid and proppants are injected at high pressure into relatively impermeable hydrocarbon reservoirs to create pathway for gas or/and oil to be drained efficiently can be more accurately located, monitored and interpreted through waveform modelling, source inversions as well as tomographic imaging. We apply full numerical simulations of wave propagation to model microseismic events in complex geological structures, and employ innovative seismic inversion methods to map detailed subsurface heterogeneities for both mining and hydraulic fracturing applications. Through the support of previous NSERC (individual) Discovery Grant and other sources of funding, I was able to establish an energetic research group composed of 2 postdocs, 8 graduate students (including 3 finished M.Sc.) and 7 undergraduates (including 2 B.Sc. theses) since I joined University of Toronto five years ago. Over the same period of time, our group published 13 papers (additionally 1 accepted, 2 under review) in peer reviewed journals. We are also co-authors on one book chapter and 2 expanded abstracts for conference proceedings. My postdocs, graduate students and I also made more than 50 conference and seminar presentations. Our research team expects to maintain a similar group size, plan for HQP training, and level of productivity for the next five years.