Collaborative Research: Adjoint tomography of fault zone environments

我们正在利用各种地震相：面波、体波、断层带首波和断层带陷波来研究断层带的地下结构。通过使用记录的地震波场的较大部分，我们应该能够更好地分辨波敏感的断层带结构。我们使用的伴随为基础的层析反演技术，依赖于高精度，三维地震波场模拟。该研究有以下三个组成部分：（1）在真实的复杂三维断层带模型中模拟合成地震记录，包括澄清产生记录的首波和陷波的观测特征的几何和材料变化的允许范围;（2）分析各种断层带、体相和地表相对深度关键断层带结构的体积敏感性;（3）Parkfield附近的San Andreas断层和San Jacinto断层带不同部分的迭代伴随层析反演。地震成核和破裂的物理环境的详细特征尚未实现。通过模拟对断层带结构特别敏感的地震波，我们可以对断层带的地下结构进行成像。断层带成像的基本困难来自其多尺度和强烈的结构变化，这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，这项研究将提供记录数据所提供的断层带结构的最详细的描述。该项目的重点是在南加州的两个社会相关的断层带。

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.