Collaborative Research: High-resolution receiver function imaging of crustal structure in the Southern Great Basin, Nevada

美国西部不断受到板块构造力的影响。在这个以内华达州南半部为中心的研究区，过去由于地壳的伸展而形成了内华达州特有的交替山脉和山谷，而最近则是美国西部沿海地区相对于大陆核心向西运动形成的。负责圣安德烈亚斯断层的西北向板块运动部分也受到加州/内华达州交界处的断层系统的影响。在15至30公里的深度，下部地壳岩石处于足够高的温度和压力下，可以变形而不发生脆性破坏。断层运动和地表运动与地壳下部形变之间的关系在很大程度上是未知的。我们的研究将使用内华达大学雷诺南部大盆地数字地震台网的地震记录来研究这一过程。这个网络探测来自全球地震的信号，这些信号被研究区域下的地壳结构修改后。通过观察来自不同方向的地震信号之间的差异，研究人员可以发现下地壳发生变形过程的迹象。在地壳的伸展和剪切过程中，下地壳有几种表现方式。在估算莫霍面深度和探测和测量地壳各向异性的多种方法中，接收函数提供了最佳选择之一。利用内华达大学Reno的短周期、密集、长期运行的南方大盆地数字地震网络收集的数据集，他们进行了一项试点研究，表明可以从这些数据中获得高质量的接收器功能。接收函数显示了来自莫霍面和地壳结构的到达，并指示了各向异性、散射和三维结构的存在。该项目计划应用多道叠加技术，包括专门针对各向异性探测的技术、用于计算接收函数的新的自举窗口技术和数值正演模拟，以区分散射和各向异性转换，并探测与构造过程有关的地壳结构。接收器功能将根据该地区的永久和临时宽带站进行校准，包括与短周期传感器位于同一网络中的少数几个宽带站。地壳结构和各向异性的发现将在内华达州西南部和加利福尼亚州东部的构造历史和发展，以及总体上的地壳下部变形的背景下进行解释。辨别哪些过程在这个研究区域正在运行，可能有助于其他研究大陆地壳变形的地球科学家了解他们所在地区的类似活动。了解地壳形变，包括下地壳发生的情况，是研究美国和其他地方的断层和地震的基础。

The western United States is continuously being deformed by plate tectonicforces. In this study area centered on the southern half of Nevada, thecharacteristic alternating ranges and valleys of Nevada were formed inthe past by stretching of the Earth's crust, and more recently, thenorthwestward motion of the western US coastal regions relative to thecore of the continent. Northwestward plate motion responsible for the SanAndreas Fault is partly also accommodated by a fault system in theCalifornia/Nevada border area. At 15 to 30 km depth, lower crustalrocks are under high enough temperature and pressure to deform withoutbrittle failure. How faulting and surface motions relate to lower crustaldeformation is largely unknown. Our study will use seismic recordings from the University of Nevada, Reno Southern Great Basin Digital Seismic Network to study this process. This network detects signals from worldwide earthquakes after they are modified by the structure of the crustunder the study area. By looking at the differences betweenearthquake signals arriving from different directions, the researchers can find signs of the deformation processes occuring in the lower crust. There areseveral ways in which the lower crust could behave during stretching andshearing of the crust. mong methods to estimate Moho depth and to detectand measure crustal anisotropy, receiver functions offer one of the bestoptions. Using a data set collected by the University of Nevada, Reno'sshort-period, dense, long-running Southern Great Basin Digital SeismicNetwork, they performed a pilot study showing that high-quality receiver functions can be obtained from the data. The receiver functions show arrivals from the Moho as well as from crustal structure, and indicate the presence of anisotropy, scattering, and 3-dimensional structure. The project plan is to apply multichannel stacking techniques, including ones specific to anisotropy detection, a new bootstrap windowing technique for receiver function calculation, and numerical forward modeling in order to distinguish scattering from anisotropic conversions and to detect crustal structures associated with tectonic processes. Receiver functions will be calibrated against permanent and temporary broadband stations in the area, including a handful of broadband stations colocated with the short-period sensors in the same network. Crustal structure and anisotropy findings will be interpreted in the context of the tectonic history and development of southwest Nevada and eastern California in particular, and lower crustal deformation in general.Distinguishing which processes are operating in thisstudy area may help other geoscientists who look at deforming continentalcrust understand similar activity in their field areas. Understandingcrustal deformation, including what happens in the lower crust, isfoundational for studies of faulting and earthquakes in the US andelsewhere.