Three-Dimensional Characterization of a Pseudotachylyte-Bearing Fault

断层滑动是地球上地壳变形的主要方式。然而，地壳内的断层表现出一系列的行为，从引发地震的粘滑到无地震蠕变。实验室得出的摩擦定律可以解释这种断层行为的频谱；然而，这些定律在天然地震条件下的刻度和对这些定律的物理意义的解释已被证明是一个巨大的挑战。这项研究将通过成像含假玄武岩的断层的三维几何图形来连接实验室和地震标尺。假玄武岩是由摩擦熔体形成的断层岩，通常被认为是断裂带中保存有地震滑动速度的唯一明确证据。摩擦熔体的凝固“冻结在”震源几何形状中；然而，它也排除了广泛的断层表面暴露的发展，这使得以前对断层带几何的研究成为可能。我们已经克服了这一困难，通过使用高分辨率X射线计算机断层扫描(CT)对断层完整的3D几何进行成像。在这项研究中，我们将使用天然和实验断层表面的CT图像来量化表面粗糙度、摩擦接触面积和假黄长石厚度，从而确定断层粗糙度随滑动的演化，并在地震成核和传播尺度上估计关键的摩擦参数。拟议中的项目将提高对地震及其影响的了解，这是国家减少地震灾害计划的主要目标之一。此外，该项目将在美国主要是本科生的卫斯理大学和意大利世界著名的研究机构国家地质学院(INGV)的科学家之间建立一种新的合作。本科生将在该项目中发挥不可或缺的作用，为未来对地壳脆性变形过程的国际和跨学科研究播下种子。这些学生将体验科学过程的全部过程，从假设的产生，到研究设计，再到在专业会议上和书面论文中展示结果。该项目得到了EAR构造计划和国际科学与工程办公室全球风险基金的支持。

Fault slip is the dominant mode of deformation in the earth's upper crust. Faults within the crust, however, exhibit a range of behavior, from earthquake-generating stick-slip to aseismic creep. Laboratory-derived friction laws can explain this spectrum of fault behavior; however, the scaling of these laws to the conditions of natural earthquakes and the interpretation of the laws' physical meanings have proven to be formidable challenges. This research will bridge laboratory and earthquake scales by imaging the three dimensional geometry of pseudotachylyte-bearing faults. Pseudotachylytes, fault rocks formed from frictional melts, are generally considered the only unequivocal evidence ofearthquake slip velocities preserved in fault zones. The solidification of frictional melt "freezes in" earthquake source geometries; however, it also precludes the development of extensive fault surface exposures that have enabled previous studies of fault zone geometry. We have overcome this difficulty by imaging the intact 3D geometry of the fault using high-resolution X-ray computed tomography (CT). In this study we will use CT imagery of natural and experimental fault surfaces to quantify surface roughness, frictional contact area, and pseudotachylyte thickness and will thus determine the evolution of fault roughness with slip and estimate key frictional parameters at earthquake nucleation and propagation scales. The proposed project will improve the understanding of earthquakes and their effects, one of the primary goals of the National Earthquake Hazard Reduction Program. Furthermore, the project will establish a new collaboration between Wesleyan University, a primarily undergraduate institution in the US, and scientists from the Istituto Nazionale di Geofisica e Vulcanologia (INGV), a world-renowned research institute in Italy. Undergraduate students will play an integral role in the project, planting the seeds for future international and interdisciplinary research into the processes of brittle deformation in the earth's crust. These students will experience the full scope of the scientific process, from hypothesis generation, to study design, to presentation of results at professional meetings and in a written thesis. The project is being supported by the EAR Tectonics Program and the Office of International Science and Engineering's Global Venture Fund.