Revealing the Nature of Contemporary Uplift and Collapse in the Sierra Nevada - Great Basin System

揭示内华达山脉-大盆地系统当代隆起和塌陷的本质

• 批准号: 0844389
• 负责人: Geoffrey Blewitt
• 金额: $ 47.49万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-04-15 至 2012-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0844389&HistoricalAwards=false
• 关键词: Revealing; Nature; Contemporary; Uplift; Collapse

How tectonically active is the Sierra Nevada today? To what extent is Great Basin extension driven internally by gravitational collapse? How do the Sierra Nevada and Great Basin interact? What is the role of the Sierra Nevada in controlling collapse and extension of the Great Basin? These questions are central to the mission of the EarthScope Program, as they represent key parts to the puzzle of how the Pacific-North America plate boundary is evolving, and what processes are responsible. Yet, despite recent advances in geodesy, we still do not have answers to simple questions that any schoolchild might ask: "How fast is the Sierra Nevada going up today?"; "Is the Great Basin going up or down?"To address these questions, this 3-year project will accurately characterize uplift and collapse in the Sierra Nevada - Great Basin region by exploiting high precision GPS data from EarthScope's Plate Boundary Observatory to measure vertical motion of the Earth's crust. These measurements will provide crucial first-order evidence on the underlying processes. Measuring vertical motion is important because it indicates the flux of potential energy, a fundamental characteristic of tectonic/mantle dynamic processes, including isostasy, orogeny (mountain building), gravitational collapse, and mantle upwelling. To make the vertical GPS data physically meaningful, methods are being implemented that will accurately reference the changes in surface height to the center of the Earth (the Earth center of mass). In order to reduce the errors in vertical rates to a useful level (sub-millimeter per year), the investigators are making use of several recent advances in GPS observable modeling, including global-scale ambiguity resolution, absolute antenna calibrations, satellite transmitter phase center variations, the modeling of non-gravitational forces on the GPS satellites, and atmospheric refraction. Once an accurate time series of vertical position is derived for each GPS station, the spatial and temporal patterns of vertical variations are then interpreted in terms of both the tectonic processes of interest, as well as non-tectonic effects (such as atmospheric pressure loading and hydrological effects).The primary data set for this project is being acquired by the specially designed "PBO Transect" of densely-spaced GPS stations, spanning east-west the entire Great Basin and Sierra Nevada range at latitude 39º-40º, together with the more broadly spaced PBO network covering the Pacific-North American plate boundary and beyond. In addition, the University of Nevada, Reno, has since 2004 built and operated the ~300-station "MAGNET" semi-continuous GPS network, which provides data for this project. Although the measurements from MAGNET are not continuous all of the time, pilot studies show that they can accurately track seasonal and secular change in GPS station height; thus MAGNET complements the continuous PBO measurements by providing much more spatial detail to the complex patterns of vertical motions. By the end of this project (mid-2012), pilot studies predict that vertical velocities for most GPS stations have an accuracy of 0.5 mm/yr, at a level that is useful for scientific interpretation, and toward answering the project's research questions.

今天的内华达山脉在构造上有多活跃？大盆地伸展在多大程度上受到重力塌陷的内部驱动？内华达山脉和大盆地是如何相互作用的？内华达山脉在控制大盆地的坍塌和伸展中扮演了什么角色？这些问题是地球范围计划任务的核心，因为它们代表了太平洋-北美板块边界如何演变以及是什么过程负责这一谜题的关键部分。然而，尽管大地测量学最近取得了进展，我们仍然没有答案来回答任何小学生可能会问的简单问题：“今天内华达山脉上升的速度有多快？”；“大盆地是上升还是下降？”为了解决这些问题，这个为期三年的项目将利用来自EarthScope的板块边界天文台的高精度GPS数据来测量地壳的垂直运动，从而准确地描述内华达山脉-大盆地地区的隆起和坍塌。这些测量将提供关于潜在过程的关键的一阶证据。测量垂直运动很重要，因为它指示了势能的流动，这是构造/地幔动力学过程的基本特征，包括均衡、造山(造山)、重力坍塌和地幔上涌。为了使垂直GPS数据具有物理意义，正在实施的方法将准确地将地表高度的变化参考到地球中心(地球质心)。为了将垂直速率的误差减少到有用的水平(每年亚毫米)，研究人员正在利用GPS观测建模方面的几个最新进展，包括全球尺度模糊分辨率、绝对天线校准、卫星发射机相位中心变化、GPS卫星上的非引力建模和大气折射。一旦得到了每个GPS站的准确的垂直位置时间序列，垂直变化的空间和时间模式就会根据感兴趣的构造过程以及非构造效应(如大气压力负荷和水文效应)来解释。该项目的主要数据集是通过专门设计的密集分布的GPS站的“PBO样带”获得的，这些样带横跨整个大盆地和内华达山脉的整个纬度39°-40°的范围，以及覆盖太平洋-北美板块边界和更远地区的更宽间距的PBO网络。此外，内华达大学雷诺分校自2004年以来已建成并运营了拥有300个站点的“磁铁”半连续GPS网络，为该项目提供了数据。尽管磁铁的测量并不总是连续的，但试点研究表明，它们可以准确地跟踪GPS站高的季节性和长期变化；因此，磁铁通过为复杂的垂直运动模式提供更多空间细节，补充了连续的PBO测量。到该项目结束时(2012年年中)，初步研究预测，大多数GPS站的垂直速度具有0.5毫米/年的精度，这一水平对科学解释和回答该项目的研究问题是有用的。