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

该项目使用熟悉的GPS卫星和科学的InSAR卫星，以毫米精度测量内华达山脉和大盆地的垂直运动，该地区横跨加州和内华达州之间的边界。该项目的第一个资助阶段的初步结果表明，内华达山脉正以惊人的速度向上移动，相对于大盆地每年约1毫米。向上的运动似乎是一个内部变形很小的固体块，尽管这需要用更详细的测量和建模进行测试。相比之下，大盆地本身的地质活动非常活跃，地震频繁，震级高，并且有可测量的东西延伸。然而，在考虑了上个世纪的地震模型之后，大盆地似乎并没有相对于地球中心向上或向下移动，在误差范围内。因此，该项目的初步结果表明，相对于地球中心，内华达山脉实际上正在上升。因此，内华达山脉似乎正在经历一次现代地质活动的爆发，并在过去几百万年里相对较快地增长到现在的高度。这个项目的目标是阐明是否确实是这样，如果是这样，如何解释它。现在这些初步结果已经公布，这个项目现在的目标是改进这些基于卫星的测量的精度和覆盖范围，以获得更准确和详细的地图，了解地球表面在研究区域上下移动的速度。精度和细节的提高使我们能够对可能与垂直运动相关的各种过程进行更高级的建模，这将有助于我们更深入地了解是什么驱动了内华达山脉的当代隆起。通过将观测期再延长4年，在分析中增加更多的GPS覆盖范围，包括本项目最近安装的新站点，以及扩大InSAR卫星数据的场景覆盖范围，这些测量正在得到加强。使我们能够确定地球质心位置的参考系在不断改进。这种发展继续减少了确定内华达山脉绝对隆升率的误差。此外，再加上大盆地发生大地震后地球如何变形的改进模型，这可能使我们能够探测到大盆地相对于地球重力场是向上移动还是向下移动，这对大盆地的历史及其今天的演变有影响，因此这可能会如何影响内华达山脉的演变。这个项目有一个更广泛的目标，即解决关于内华达山脉隆起背后的历史和机制的长期争议，现代地形的年龄估计（在这个项目之前）在300万年到6000万年之间，我们的项目倾向于早期的情景。如果结果成立，它们将有助于限制大盆地演化的模型，因为从古峡谷的地质分析中可以知道，西翼一定在某个时候受到重力的作用而坍塌，成为现代的大盆地。因此，从许多角度来看，理解这个系统的隆起和崩塌是很重要的，包括北美和太平洋之间板块边界的过去和未来的演变，今天活动断层（包括圣安德烈亚斯断层）的压力，以及解释这个地震活跃地区的应变和断层的变化。因此，该项目为了解地震可能发生的时间和地点提供了更广泛的计划，并帮助做好准备的公民了解地震危害。这个项目的另一个更广泛的好处是，地球表面也会因为地下有水而上下移动。因此，这个项目的数据也被用来探索其在改善这个大部分干旱地区的大规模水文模型方面的效用，以帮助解决管理和维持水资源方面的挑战。

This project uses the familiar GPS satellites together with scientific InSAR satellites to measure with millimeter precision the vertical movement of the Sierra Nevada mountain range and Great Basin in the region spanning the border between California and Nevada. Initial results from the first funded phase of the project show that the Sierra Nevada are moving upward at a surprisingly fast rate of about 1 millimeter per year relative to the Great Basin. The upward movement appears to be that of a solid block with little internal deformation, though this requires testing with more detailed measurements and modeling. In contrast, the Great Basin itself is known to be very geologically active, with frequent earthquakes up to large magnitudes, and with measurable east-west extension. Yet, after accounting for models of earthquakes over the last century, the Great Basin does not appear to move up or down relative to the center of the Earth to within the margins of error. Therefore the project's initial results indicate that the Sierra Nevada are actually uplifting relative to the center of the Earth. It would therefore appear that the Sierra Nevada are undergoing a modern spurt of geological activity, and have grown to their present height relatively quickly in the last few million years. The goal of this project is to shed more light as to whether this is indeed the case, and if so, how can it be explained.Now that these initial results are published, the objective of this project now is to refine the precision and coverage of these satellite-based measurements to get a more accurate and detailed map of how fast the Earth's surface is moving up and down in the study region. Enhanced precision and detail are allowing for more advanced modeling of the various processes that may be associated with vertical movement, that should lead to a stronger understanding of what may be driving contemporary uplift in the Sierra Nevada. The measurements are being enhanced by extending the observational period by another 4 years, by adding more GPS coverage to the analysis, including new stations recently installed by this project, and by extending the coverage of scenes from InSAR satellite data. The reference system that enables us to locate the center of mass of the Earth continues to be improved. This development continues to reduce the error in determining the absolute uplift rate of the Sierra Nevada. Moreover, together with improved models of how the Earth deforms following large earthquakes in the Great Basin, this may allow us to detect whether the Great Basin is moving up or down with respect to the Earth's gravity field, which has implications as to the Great Basin's history and how it is evolving today, and therefore how this might influence the evolution of the Sierra Nevada.This project has the broader goal of addressing a long-standing controversy about the history and mechanisms behind uplift of the Sierra Nevada, with the age of modern topography estimated (prior to this project) between 3 to 60 million years old, with our project favoring the earlier scenario. If the results hold up, they will help to constrain models the evolution of the Great Basin, as it is known from geological analysis of ancient canyons that the western flank must at some point have gravitationally collapsed to become the modern Great Basin. Understanding uplift and collapse of this system is thus important from many perspectives, including the past and future evolution of the plate boundary between North America and the Pacific, the stresses on active faults today (including the San Andreas Fault), and explaining the variation in style of strain and faulting across this seismically active region. Thus the project feeds into a broader program of understanding when and where earthquakes are likely to occur, and help inform prepare citizens on seismic hazards. Another broader benefit of this project is that the Earth's surface also moves up and down from the presence of water in the ground. Thus data from this project is also being used to explore its utility in improving large-scale models of hydrology in this largely arid region, to help address challenges in managing and sustaining water resources.