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

在大陆转换断层，如圣安德烈亚斯，一个构造板块相对于其邻近板块水平滑动。由于这些断层位于陆地上，而且往往位于人口稠密的地区，因此引发的地震极大地影响了当地人口。关于板块如何在浅层(约10公里)下变形，这是地震的发源地，仍然存在争议。在更大的深度，下伏的岩石从脆性变形过渡到韧性变形。但断层下的剪切带是否在数十公里内保持狭窄，或者变形是否立即扩大尚不清楚。这些不同的情景会影响断层的加载方式，并对地震危险性评估产生重大影响。在这里，该团队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择优取向和组构，这可以用地震波检测到。这是因为岩石组构影响波速，然后波速取决于传播方向。通过分析地震波在断层下传播的各向异性，研究人员探索了岩石变形的几何和程度。他们还使用受地质观测约束的地球动力学模型；对于给定的断层几何形状和变形属性，他们预测断层下的地震各向异性特征。通过比较观测和预测，该团队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。它为一名女研究生提供支持和培训，并向本科生和K12学生--特别是在科学界代表性不足的群体--和公众提供服务。该团队使用了横跨六个大陆转换断层(圣安德烈亚斯、北安纳托利亚、德纳利、新西兰阿尔卑斯山、阿尔金/昆仑和死海)的现有部署数据。它进行了远震横波分裂的全波形二维和三维模拟，以及各向异性接收函数分析。目标是成像每个转换断层周围的剪切带和更广泛的形变场。选定的断层代表了不同年龄和成熟度的转换。现有的分裂观测显示了断层之间的系统对比。结合高分辨率剪切带成像和地球动力学模拟，研究人员调查了岩石圈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结构的可能作用。该项目是朝着建立大陆岩石圈转换模型和更好地评估相应的地震危险迈出的关键一步。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.