Collaborative Research: Adjoint tomography of fault zone environments

我们利用各种地震相：面波、体波、断裂带头波和断裂带陷波来研究断裂带的地下结构。通过使用记录的地震波场的更大部分，我们应该能够更好地分辨出地震波敏感的断裂带结构。我们使用基于伴随的层析反演技术，该技术依赖于高精度的三维地震波场模拟。该研究包括以下三个部分：(1)在真实复杂的三维断裂带模型中模拟合成地震记录，包括澄清产生记录头波和捕获波观测特征的几何和物质变化的允许范围；(2)各断裂带、体和地表相对深部关键断裂带构造的体积敏感性分析；(3)帕克菲尔德附近圣安德烈亚斯断层和圣哈辛托断裂带不同剖面构造的迭代伴随层析反演。破坏性大地震起源于地表以下几公里处的断层。对地震成核和破裂的物理环境的详细描述尚未实现。通过模拟对断裂带构造特别敏感的地震波，我们可以对断裂带的地下结构进行成像。断层成像的基本困难在于其多尺度和强烈的结构变化，这种变化在地表和钻孔内都很明显。通过使用精确的地震波传播模型，该研究将提供记录数据提供的最详细的断裂带结构描述。该项目重点关注南加州两个与社会相关的断层带。

We are investigating the subsurface structure of fault zones using a variety of seismic phases: surface waves, body waves, fault zone head waves, and fault zone trapped waves. By using a larger portion of the recorded seismic wavefield, we should be able to better resolve the fault zone structures to which the waves are sensitive. We use an adjoint-based tomographic inversion technique that relies on highly accurate, three-dimensional seismic wavefield simulations. The study has the following three components: (1) simulations of synthetic seismograms in realistic, complex 3D fault zone models, including clarifying the allowable ranges of geometrical and material variations that produce the observed characteristics of recorded head and trapped waves; (2) analysis of volumetric sensitivities of various fault zone, body, and surface phases to key fault zone structures at depth; (3) iterative adjoint tomographic inversions for the structures of the San Andreas fault near Parkfield and different sections of the San Jacinto fault zone.Large damaging earthquakes originate on faults kilometers below Earth's surface. A detailed characterization of the physical setting where earthquakes nucleate and rupture has not yet been achieved. By modeling seismic waves that are particularly sensitive to the structures of fault zones, we can image the subsurface structure of fault zones. The basic difficulty in imaging fault zones stems from their multi-scale and strong variations in structure, which are evident at the surface and within boreholes. By using accurate seismic wave propagation models, the study will provide the most detailed description of fault zone structure afforded by the recorded data. The project focuses on two societally relevant fault zones in southern California.