Using 230Th/U Dating of Pedogenic Carbonate to Provide a Time-Axis for Slip on the Elsinore Fault, Southern California

利用成土碳酸盐的 230Th/U 测年为南加州埃尔西诺断层上的滑动提供时间轴

• 批准号: 0636053
• 负责人: Warren Sharp
• 金额: $ 12.17万
• 依托单位: Berkeley Geochronology Center
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-02-01 至 2009-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0636053&HistoricalAwards=false
• 关键词: Using; 230Th; Dating; Pedogenic; Carbonate

Continental plate boundaries commonly consist of broad regions of deformation characterized by fault systems consisting of multiple, approximately parallel faults, such as the San Andreas fault system of California. To better quantify the seismic hazard posed by such faults, it is essential to determine their pattern of motion through time. While recent advances in geodetic observations in the vicinity of plate boundary fault systems provide unprecedented insight into patterns of crustal deformation on the relatively short (i.e., decadal) timescale, it is likely that over longer timescales seismogenic faults exhibit variable displacement rates. That is, slip rates derived from geodetic data may reflect transient motions associated with large earthquakes in the recent past, or other recent changes in crustal loading. On a longer timescale, slip rates on major faults such as the San Andreas of southern California are thought to have varied by about a factor of two within the last approximately100,000 years. Such variability, if confirmed, could perhaps result from redistribution of slip due to evolving crustal structural complexities, clustering of earthquakes on intermediate timescales (i.e., approximately 10,000 years), or other mechanisms. Quantifying fault slip rates on timescales of 1 to 100,000 years is therefore fundamental to an improved understanding of continental dynamics and will serve societal needs for improved quantification of seismic hazards near major fault systems. Reliable measurements of fault slip on the timescale of 1 to 100,000 years, however, are quite limited in number. This is in part because of the relative rarity of geological situations that preserve the appropriate stratigraphic or geomorphologic information needed to precisely determine offsets on active faults. A second and equally demanding requirement for determining long-term slip rates, however, is that offset strata or landforms must be reliably dated, and existing methods for dating geologically young surfaces and strata only partially meet this demand. A novel technique for determining the age of landforms offset by faulting will be developed and applied in this research project. Specifically, the project will extend and further develop small-sample, high precision 230Th/U dating of soil carbonate via mass spectrometry. The results will provide unprecedented insight into the constancy (or lack thereof) of slip rates over time on the Elsinore fault, a principal strand of the San Andreas fault system in southern California, over a range of intervals in the past approximately 100,000 to 200,000 years.The research project will further develop a novel means of dating geologically youthful landforms, extend the capacity and capability of earth scientists to determine fault slip rates in arid regions worldwide, and help to address societal needs for more quantitative assessment of seismic hazards. The project will also provide comprehensive training in innovative techniques of geochronology for doctoral candidate.

大陆板块边界通常由广泛的变形区域组成，其特征是由多个近似平行的断层组成的断层系统，例如加利福尼亚的圣安德烈亚斯断层系统。为了更好地量化这些断层所造成的地震危险，确定它们随时间的运动模式是至关重要的。虽然最近在板块边界断层系统附近的大地测量观测取得了进展，为在相对较短的时间尺度（即十年）上的地壳变形模式提供了前所未有的见解，但在较长的时间尺度上，发震断层很可能表现出可变的位移率。也就是说，从大地测量数据得出的滑动率可能反映与最近的大地震有关的瞬态运动，或最近地壳载荷的其他变化。在更长的时间尺度上，像南加州的圣安德烈亚斯断层这样的主要断层的滑动率被认为在过去大约10万年里发生了大约两倍的变化。这种变异性如果得到证实，可能是由于地壳结构复杂性的演变、中间时间尺度（即大约1万年）上的地震聚集或其他机制引起的滑动重新分布造成的。因此，在1至10万年的时间尺度上量化断层滑动率对于提高对大陆动力学的理解至关重要，并将满足社会对主要断层系统附近地震危险量化的需求。然而，在1到10万年的时间尺度上对断层滑动的可靠测量在数量上是相当有限的。这在一定程度上是因为保存了精确确定活动断层偏移所需的适当地层或地貌信息的地质情况相对稀少。然而，确定长期滑移率的第二个也是同样苛刻的要求是，偏移地层或地形必须可靠地定年，而现有的地质年轻表面和地层定年方法只能部分满足这一要求。本研究项目将发展并应用一种确定断层偏移地貌年龄的新技术。具体来说，该项目将扩展和进一步发展小样本、高精度230Th/U土壤碳酸盐质谱测年技术。这一结果将为埃尔西诺断层在过去大约10万到20万年的时间间隔内滑动速率的恒定（或不恒定）提供前所未有的见解。埃尔西诺断层是南加州圣安德烈亚斯断层系统的主要分支。该研究项目将进一步开发一种确定地质年轻地貌年代的新方法，扩展地球科学家确定全球干旱地区断层滑动率的能力，并帮助解决对地震危害进行更多定量评估的社会需求。该项目还将为博士候选人提供全面的地质年代学创新技术培训。