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卫星和科学干涉合成孔径雷达卫星，以毫米精度测量加州州和内华达州边界地区的内华达州山脉和大盆地的垂直运动。 该项目第一个资助阶段的初步结果显示，相对于大盆地，内华达州山脉正以每年约1毫米的惊人速度向上移动。 向上的运动似乎是一个固体块体，内部几乎没有变形，尽管这需要更详细的测量和建模测试。相比之下，大盆地本身的地质活动非常活跃，地震频繁，震级很大，而且东西向延伸。然而，在解释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上下移动到误差范围内。 因此，该项目的初步结果表明，内华达州山脉实际上是相对于地球中心上升。因此，内华达州山脉似乎正在经历一场现代地质活动的井喷，并在过去的几百万年里相对较快地发展到目前的高度。 该项目的目标是进一步阐明这是否是事实，如果是的话，如何解释。现在这些初步结果已经公布，该项目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，了解研究区域的地球表面上下移动的速度。 提高精度和细节允许更先进的建模的各种过程，可能与垂直运动，这应该导致一个更好的理解可能是什么驱动当代隆起的内华达州。 通过将观测期再延长4年、在分析中增加更多的全球定位系统覆盖范围（包括该项目最近安装的新台站）以及扩大干涉合成孔径雷达卫星数据的场景覆盖范围，正在加强测量工作。 使我们能够确定地球质心位置的参考系统继续得到改进。 这一发展继续减少确定内华达州山脉绝对抬升速率的误差。 此外，再加上大盆地大地震后地球如何变形的改进模型，这可能使我们能够检测大盆地相对于地球重力场是向上还是向下移动，这对大盆地的历史和它今天的演变有影响，因此，这可能如何影响内华达州的演变。这个项目有更广泛的目标，解决一个长期的-关于内华达州山脉隆起的历史和机制的长期争议，现代地形的年龄估计（在本项目之前）在300万年到6000万年之间，我们的项目倾向于更早的情况。 如果结果成立，它们将有助于限制大盆地演化的模型，因为从古代峡谷的地质分析中得知，西部侧翼必须在某个时候重力坍塌，成为现代大盆地。 因此，从许多角度理解该系统的隆起和塌陷都很重要，包括北美和太平洋之间板块边界的过去和未来演变，今天活动断层（包括圣安德烈亚斯断层）的应力，以及解释整个地震活动区的应变和断层类型的变化。 因此，该项目有助于了解地震可能发生的时间和地点，并帮助公民做好地震危险的准备。 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水的存在而上下移动。 因此，该项目的数据也被用于探索其在改善这一大部分干旱地区的大型水文模型方面的效用，以帮助应对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.