Collaborative Research: Late Cenozoic Vertical Crustal Motions and Erosional Mass Transfer in the Southern San Andreas Fault Zone

合作研究：圣安德烈亚斯断裂带南部的晚新生代地壳垂直运动和侵蚀质量传递

• 批准号: 1145067
• 负责人: Michele Cooke
• 金额: $ 6.61万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-02-15 至 2015-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1145067&HistoricalAwards=false
• 关键词: Collaborative; Research; Late; Cenozoic; Vertical

Vertical crustal motions are widely recognized in continental strike-slip fault zones, yet the underlying controls and surficial response to 3-dimensional strain in these settings are poorly understood. Observed patterns of uplift and subsidence often do no match the predictions of numerical models for oblique strain, suggesting that existing models for strike-slip faults are incomplete. Structural controls on development of sedimentary basins in strike-slip fault zones are similarly complex and incompletely understood. This project is addressing these problems with a multi-disciplinary, multi-investigator study of 3-dimensional strain and related surface processes in the San Andreas fault zone of southern California. The research team will use a diverse suite of methods to document rates and geometries of vertical crustal motions through time, and test two hypotheses for the evolution of the San Andreas fault: (1) that plate-motion obliquity exerts the primary control on the 3-dimensional and temporal evolution of the fault zone; and (2) that the fault zone experienced a major change at approximately 1.1 to 1.4 million years ago in response to tectonic reorganization of the plate boundary. Each hypothesis makes unique predictions about space-time patterns of uplift, erosion, subsidence, and sediment dispersal within the fault zone, that will allow the team to test the hypotheses with a systematic program of fieldwork, data analysis, and modeling. This project integrates diverse research methods including geologic mapping, stratigraphic and structural analysis, paleomagnetic studies of sediment age and block rotations, provenance analysis, detrital zircon dating, low-temperature (U-Th)/He dating of bedrock sources, geomorphic analysis, study of seismic and gravity data, and numerical modeling.This study seeks to fill large gaps in the understanding of the geologic evolution of the southern San Andreas fault system, a complex network of seismically active faults that define the Pacific-North America plate boundary in California. The history of deformation over geologic timescales (millions of years) is relatively poorly known, despite its critical role in shaping the crustal architecture and fault geometries that control earthquakes in this setting. This project's approach benefits from a unique collaboration of academic researchers and students from four universities with earth scientists at the U.S. Geological Survey. The team is also collaborating with geophysicists investigating processes of continental rupture beneath the Salton Sea, and scientists studying paleoseismology and fault slip rates on the San Andreas fault over shorter timescales. These collaborations provide an important avenue for engaging with and contributing new knowledge to the vibrant geoscience community in southern California. Lessons learned in this research will be used to develop new lab and teaching exercises that will reach thousands of students over the course of the project. Ultimately, the results of this study will shed new insights into dynamic linkages between crustal deformation, fault-zone complexity, growth of topography, erosion, and sediment dispersal within continental strike-slip fault zones at active plate boundaries.

在大陆走滑断裂带中，地壳垂直运动已被广泛认识，但对这些构造中的三维应变的基本控制和地表响应却知之甚少。观察到的隆起和沉降模式往往与斜应变数值模型的预测不匹配，这表明现有的走滑断层模型是不完整的。走滑断裂带中构造对沉积盆地发育的控制作用也同样复杂，而且尚未完全了解。本项目通过对南加州圣安德烈亚斯断层带的三维应变和相关表面过程进行多学科、多调查员研究来解决这些问题。研究小组将使用一套不同的方法来记录地壳垂直运动的速率和几何形状，并测试圣安德烈亚斯断层演化的两个假设：（1）板块运动的平行性对断层带的三维和时间演化起主要控制作用;（2）断裂带在大约110万至140万年前经历了一次重大变化，以响应板块边界的构造重组。每个假设都对断层带内隆起、侵蚀、沉降和沉积物扩散的时空模式做出了独特的预测，这将使研究小组能够通过系统的实地考察、数据分析和建模来测试这些假设。该项目综合了多种研究方法，包括地质填图、地层和构造分析、沉积年龄和地块旋转的古地磁研究、物源分析、碎屑锆石定年、基岩源的低温（U-Th）/He定年、地貌分析、地震和重力数据研究、和数值模拟。这项研究旨在填补在南部圣安德烈亚斯断层系统的地质演化的理解，一个复杂的地震活动断层网络，定义了加州的太平洋-北美板块边界。地质时间尺度（数百万年）上的变形历史相对知之甚少，尽管它在塑造地壳结构和断层几何形状方面发挥着关键作用，这些结构和断层几何形状控制着这种环境中的地震。该项目的方法得益于来自四所大学的学术研究人员和学生与美国地质调查局地球科学家的独特合作。该团队还与研究索尔顿海下大陆断裂过程的地质学家合作，并与研究圣安德烈亚斯断层在较短时间尺度上的古地震学和断层滑动率的科学家合作。这些合作提供了一个重要的途径，参与和贡献新的知识，以充满活力的地球科学界在南加州。在这项研究中学到的经验教训将用于开发新的实验室和教学练习，将达到成千上万的学生在项目的过程中。最终，这项研究的结果将揭示地壳变形，断裂带的复杂性，地形，侵蚀和沉积物分散在大陆走滑断裂带在活动板块边界的增长之间的动态联系的新见解。