Collaborative Research: Structure and depth extent of lithospheric shear zones surrounding continental transform faults

在圣安德烈亚斯等大陆转换断层处，一个构造板块相对于其相邻板块水平滑动。由于此类断层位于陆地上，并且通常位于人口稠密地区，因此引发的地震会对当地人口产生巨大影响。关于板块如何在产生地震的浅层（~10公里）顶层变形仍然存在争议。在较大深度，下伏岩石从脆性变形转变为延性变形。但断层下方的剪切带是否在数十公里内保持狭窄，或者变形是否立即变宽，尚不清楚。这些不同的情况会影响断层的加载方式，并对地震灾害评估具有重大影响。在这里，研究小组利用现有的地震记录来调查六个主要的大陆转换断层。变形的岩石通常表现出晶体的择优取向、结构，可以用地震波检测到。这是因为岩石结构会影响波速，而波速又取决于传播方向。通过分析穿过断层带下方的地震波的各向异性，研究人员探索了岩石变形的几何形状和程度。他们还使用受地质观测限制的地球动力学模型；对于给定的断层几何形状和变形特性，他们预测断层下方的地震各向异性特征。通过比较观测和预测，研究小组揭示了大陆转换断层的变形行为。该项目促进了与澳大利亚和瑞士的国际合作。它为女研究生提供支持和培训，并为本科生和 K12 学生（尤其是来自科学界代表性不足的群体）和公众提供服务。 该团队使用跨越六个大陆转换断层（圣安地列斯、北安纳托利亚、麦金利、新西兰高山、阿尔金塔格/昆仑和死海）的现有部署的数据。它对远震剪切波分裂进行全波形 2D 和 3D 建模，以及各向异性接收函数分析。目标是对每个转换断层周围的剪切带和更广泛的变形场进行成像。所选断层代表了不同年龄和成熟度的转变。现有的分裂观测显示了断层之间的系统对比。研究人员结合高分辨率剪切带成像和地球动力学建模，研究了岩石圈中的应变局部化程度和剪切带几何形状。他们还研究了机械各向异性和遗传织物的可能作用。该项目是建立大陆岩石圈转变模型和更好地评估相应地震危害的关键一步。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。

At continental transform faults such as the San Andreas, one tectonic plate slides horizontally relative to its neighbor. Because such faults lie on land and often in populated areas, the resulting earthquakes dramatically impact local populations. It remains debated how plates deform beneath the shallow (~10 km), top layer where earthquakes are generated. At larger depths, underlying rocks transition from brittle to ductile deformation. But whether the shear zone underneath the fault remains narrow for tens of km, or whether deformation widens right away is not clear. These different scenarios affect how faults are loaded, and have significant implications for seismic hazard assessment. Here, the team uses existing seismic records to investigate six major continental transform faults. Deformed rocks often exhibit crystal preferred orientations, fabrics, that can be detected with seismic waves. This is because rock fabrics affect the wave velocity which then depends on the propagation direction. By analyzing the anisotropy of seismic waves passing underneath the fault zones, the researchers probe the geometry and extent of rocks deformation. They also use geodynamic modeling constrained by geological observations; for given fault geometries and deformation properties, they predict seismic anisotropy features underneath the faults. By comparing observations and predictions, the team unravels the deformation behavior of continental transform faults. The project fosters an international collaboration with Australia and Switzerland. It provides support and training to a female graduate student, and outreach toward undergraduates and K12 students - notably from group underrepresented in Sciences - and the public. The team uses data from existing deployments crossing six continental transform faults (San Andreas, North Anatolian, Denali, New Zealand Alpine, Altyn Tagh/Kunlun, and Dead Sea). It conducts full-waveform 2-D and 3-D modeling of teleseismic shear wave splitting, as well as anisotropic receiver function analysis. The goal is to image the shear zone and broader deformation field surrounding each transform fault. The selected faults represent transforms of different ages and maturity. Existing splitting observations show systematic contrasts between faults. Combining high-resolution shear zone imaging and geodynamic modeling, the researchers investigate the degree of strain localization in the lithosphere and the shear zone geometry. They also study the possible roles of mechanical anisotropy and inherited fabrics. This project is a critical step toward establishing a model for continental lithospheric transforms and better assessing the corresponding earthquake hazards.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.