Full waveform inversions and source characterization based on spectral-element simulations: innovative datasets and inversion strategies

地震成像是基于穿越地球内部的地震波绘制的地下结构图，它生成了令人着迷的地壳和地幔图像，这些图像被证明对于理解形成地球构造演化的地球动力学过程和地质事件至关重要。另一方面，地震学致力于了解地震，这是对人类破坏最大的自然灾害之一，包括其位置，震源机制，地震波传播和诱发地面震动的强度。收集这些基本信息为长期地震灾害评估和风险缓解提供了重要指导，特别是对地震多发地区而言。基于精确的数值方法（如过去二十年中发展起来的谱元法）模拟地震波传播的能力，使创新的、基于数值模拟的全波形反演（FWI）技术能够应用于高分辨率成像，以及基于复杂背景模型的三维格林函数的震源反演。我们的团队继续致力于基于开源最先进的SEM软件包开发FWI功能的最前沿，并通过提高其数值效率和探索新的反演策略来促进更广泛的地震社区的采用。我们还将FWI应用于创新的数据集，如环境噪声和电磁体波，用于阵列成像。我们计划生成第一个高分辨率的各向同性和径向各向异性模型的地壳和最上层的地幔的整个阿拉斯加地区的基础上，多分量的环境噪声FWI。本文提出了一种联合环境噪声和地震波的FWI方法，利用这两种数据集的互补灵敏度，并将联合FWI应用于加州板块边界地区的高分辨率成像。我们还探讨了基于格林函数的震源反演方法，该方法通过SEM求解器为改进的3D区域模型计算。我们建议开发高效的工作流程，近实时源机制反演的基础上存储的三维数值应变-格林张量（SGT）数据库，可以采用作为一个定期的地震网络操作。这些新开发的结构成像和震源反演能力将使我们成为领先的计算地震学研究小组之一，并有助于培养下一代HQP，这些HQP配备了并行计算，大型地震数据集处理，先进成像和震源表征方法以及机器学习方面的关键技能。

Seismic imaging, the mapping of subsurface structures based on seismic waves traversing through the Earth's interior, has generated fascinating images of the Earth's crust and mantle which prove to be critical for understanding geodynamic processes and geological events that shaped the tectonic evolution of the Earth. On the other hand, 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 this essential information offers crucial guidance on long-term seismic hazard assessment and risk mitigation, especially for earthquake-prone regions. The capability to simulate seismic wave propagation based on accurate numerical methods, such as the spectral-element method (SEM) developed in the past two decades, enabled the application of innovative, numerical-simulation-based full waveform inversion (FWI) techniques for high-resolution imaging, as well as seismic source inversions based on 3D Greens functions for complex background models. Our group continues to work at the forefront of developing capabilities for FWI based on open-source state-of-the-art SEM software packages and facilitate its adoption by the wider seismic community by improving its numerical efficiency and exploring new inversion strategies. We also apply FWI to innovative datasets, such as ambient-noise and teleseismic body waves, for array imaging. We plan to generate the first high-resolution isotropic and radially anisotropic models for the crust and upper-most mantle of the entire Alaska region based on multi-component ambient-noise FWI. we propose to develop joint ambient-noise and teleseismic-wave FWI method to take advantage of the complementary sensitivity of these two datasets, and apply the joint FWI to high-resolution imaging beneath central California plate boundary region. We also explore source inversion methods based on Greens functions computed for improved 3D regional models by SEM solvers. We propose to develop efficient workflows for near-realtime source mechanism inversions based on the storage of 3D numerical strain-Greens tensor (SGT) database that can be adopted as a regular seismic network operation. These newly developed structural imaging and source inversion capabilities will strength us as one of the leading computational seismology research groups and help train next-generation HQPs equipped with critical skills in parallel computing, large seismic dataset processing, advance imaging and source characterization methods, and machine learning.