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: 1145115
• 负责人: James Spotila
• 金额: $ 7.74万
• 依托单位: Virginia Polytechnic Institute and State University
• 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 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1145115&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.

地壳垂直运动在大陆走滑断层带中被广泛认识，但对这些环境中三维应变的底层控制和地表响应知之甚少。观测到的隆起和沉降模式通常与斜应变数值模型的预测不符，这表明现有的走滑断层模型是不完整的。走滑断裂带沉积盆地发育的构造控制同样复杂且不完全清楚。该项目正在通过对南加州圣安德烈亚斯断层带的 3 维应变和相关表面过程进行多学科、多研究者研究来解决这些问题。研究小组将使用多种方法来记录地壳垂直运动随时间变化的速率和几何形状，并测试关于圣安德烈亚斯断层演化的两个假设：(1) 板块运动倾角对 3 个断层发挥主要控制作用。 -断层带的维度和时间演化； (2) 断裂带在大约 1.1 至 140 万年前经历了一次重大变化，响应板块边界的构造重组。每个假设都对断层带内的隆起、侵蚀、沉降和沉积物扩散的时空模式做出了独特的预测，这将使团队能够通过现场工作、数据分析和建模的系统程序来检验这些假设。该项目整合了多种研究方法，包括地质测绘、地层和结构分析、沉积物年龄和块体旋转的古地磁研究、物源分析、碎屑锆石测年、基岩源低温（U-Th）/He测年、地貌分析、研究这项研究旨在填补对圣安德烈亚斯断层系统南部地质演化理解的巨大空白，圣安德烈亚斯断层系统是一个复杂的地震活动断层网络，定义了北太平洋地区美洲板块边界位于加利福尼亚州。尽管地质时间尺度（数百万年）的变形历史在塑造控制地震的地壳结构和断层几何形状方面发挥着关键作用，但人们对它的了解相对较少。该项目的方法得益于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。该团队还与地球物理学家合作，研究索尔顿海下方的大陆破裂过程，并与科学家合作，研究古地震学和圣安德烈亚斯断层在较短时间尺度上的断层滑动率。这些合作为参与南加州充满活力的地球科学界并为其贡献新知识提供了重要途径。这项研究中吸取的经验教训将用于开发新的实验室和教学练习，这些练习将在项目过程中惠及数千名学生。最终，这项研究的结果将为活动板块边界的大陆走滑断层带内地壳变形、断层带复杂性、地形生长、侵蚀和沉积物扩散之间的动态联系提供新的见解。