Using Geodesy to Separate Transient and Steady Extension in the Basin and Range Province, Western United States

盆地和山脉省是太平洋/北美板块边界变形带的一个组成部分，它经历的大地震可能威胁到内华达州、犹他州、亚利桑那州、爱达荷州和俄勒冈州的社区。这个800公里宽的省份的活动变形现在可以用GPS等空间大地测量方法精确测量，因此现在有可能绘制出产生导致这些地震的应力的缓慢运动的速率和样式。然而，最近的地质和地球物理研究得出了相互矛盾的结论，即内华达州的变形是如何发生的。一些大地测量学研究表明，北美板块在内华达州东部没有变形，而另一些研究则发现了间歇性、大规模、但规模较小的变形事件的证据。地质证据表明，近期正断层和伸展活动在全省范围内大致均匀分布。关于北美板块如何变形的这三种不同观点意味着大陆岩石圈伸展的三种截然不同的动力模式，因此不可能三种观点都是正确的。EarthScope板块边界观测站GPS网络是根据美国50号州际公路沿线站点的剖面设计的，这些站点横跨北纬39度左右的整个盆地和山脉，这些GPS站点现在正在检测内华达州东部的个位数纳米应变/年变形率。因此，PBO已经准备好解决构造大地测量学的新前沿：在板块边界的主要元素之间传递变形的缓慢但活跃的领域。为了区分这三种假设，我们将：1)使用最新的软件和模型处理GPS数据；2)系统地生成大地瞬态数据目录；3)开发改进的19世纪和20世纪地震粘弹性响应模型，从GPS时间序列中去除震后瞬态信号；4)估计内华达州东部长期变形的速率和模式，并将这些结果与地质和地震数据进行比较。这些活动的结果将提高对活动板块边界的内容物如何变形的理解。通过这样做，我们将量化驱动地震发生的背景构造变形的速率、模式和风格。这些比率越来越多地被用于指导建筑实践的美国国家地震危险地图。因此，这项工作将对地震的准备工作和对未来地震损失的估计产生直接影响。

The Basin and Range Province is an integral part of the Pacific/North America plate boundary deformation zone, and experiences large earthquakes that can threaten communities in Nevada, Utah, Arizona, Idaho and Oregon. The active deformation of the 800 km wide Province can now be precisely measured with space geodetic methods such as GPS, and thus it is now possible to chart the rates and styles of the slow movements that generate the stresses that cause these earthquakes. However, recent geological and geophysical studies have come to conflicting conclusions about how the deformation across Nevada occurs. Some geodetic studies have suggested that the North American Plate is non-deforming in eastern Nevada, while others have found evidence for episodic, large-scale, but small magnitude deformation events. Geologic evidence suggests that recent normal faulting and extension occurs and is distributed roughly evenly across the Province. These three different views of how the North American plate deforms imply three extremely different dynamic modes of extension of continental lithosphere, and thus it is not possible that all three are correct. The EarthScope Plate Boundary Observatory GPS network was designed with a profile of sites along US Interstate Highway 50, across the entire Basin and Range at a latitude of about 39 degrees N. These GPS sites are now detecting single digit nanostrain/yr deformation rates across eastern Nevada. Therefore PBO is ready to address this new frontier in the science of tectonic geodesy: The slow but active realms that transfer deformation between the major elements of the plate boundary. To distinguish between the three hypotheses we will: 1) process GPS data using the latest software and models, 2) systematically generate a catalog of geodetic transients, 3) develop improved models of the viscoelastic response of 19th and 20th century earthquakes to remove postseismic transient signals from the GPS time series, 4) estimate rates and patterns of long term deformation of eastern Nevada and compare these results to geologic and seismic data.The results of these activities will be an improved understanding of how the contents in active plate boundaries deform. In so doing we will quantify the rate, pattern, and style of background tectonic deformation that drives the occurrence of earthquakes. These rates are increasingly being used in the U.S. National Seismic Hazard Maps that guide building practices. Thus this work will have a direct impact on preparedness for and estimates of future losses from earthquakes.