Collaborative Research, RUI: Geodetic and Geologic Study of the Kinematics of Late Cenozoic Displacement Transfer, Central Walker Lane, Western Great Basin

晚新生代变形广泛分布在美国西部相连的北美板块边缘，从圣安德烈亚斯断层系向东延伸，穿过莫哈韦沙漠，进入盆地和山脉。东加州剪切带和西大海盆的步行者巷构成了一个构造活动带，它容纳了北美板块和太平洋板块之间约25%的相对运动。从莫哈韦沙漠开始，位移被带到北部，内华达州南部山脉以东，在西部和东部由欧文斯谷和炉溪断层系统界定的狭窄变形区。从内华达州中部向北，变形带扩大到包括步行者巷和大盆地西北部的内华达州中部地震带。Sierra内华达州表现为一个具有10-14 mm/年的西北向运动的连贯构造块体，并形成大盆地分布变形带的西边界。内华达州中西部下方有一个复杂的活动构造格局，位移从加州东部剪切带转移到步行者巷和内华达州中部地震带。综合地质、地震和GPS大地测量结果表明，中央步行者巷作为一个位移传递系统，连接着阶梯状的西北向横断层。在中央步行者车道位移分区是积极的，并可能容纳的构造块体的差异运动。一个GPS速度场表现出一个系统的增加幅度从东到西的中央步行者巷，是一致的块平移和垂直轴旋转。在可疑的块体边界上观察到发散、横向和会聚运动带。观测到的速度场与目前对断层位移的理解不容易协调，并指出了比较大地测量和地质位移场的困难。PI建议对中央步行者巷进行综合大地测量和地质调查，以解决两个问题：（1）平移构造之间的位移传递是否完全由贯通断层上的运动学协调滑动来调节，由GPS大地测量得到的主动位移传递运动学与地震学和断层滑动反演得到的位移场是否一致？中央步行者巷非常适合这项研究，原因有三：（1）该地区地震活跃，位移传递断层系统存在明确的地震震源机制，（2）断层暴露良好，并产生了变形运动学的初步断层滑动估计，（3）GPS大地网记录到了一个复杂的现代位移场，其差异滑动量约为10 mm/yr。这些元素将允许位移传递的运动学特性，并提供直接比较不同的测量变形运动学的方法的机会。PI的主要兴趣是描述主动位移传递步距中变形的运动学特征，并将大地测量确定的位移场与来自地震震源机制和断层滑动反演的位移场进行比较。为了实现他们的研究目标，暴露在中央步行者巷的延伸跨越系统的几个方面必须更详细地检查。该项目规定的主要任务是：（1）建立连接边界横断层的活动高角度断层的空间分布，（2）记录横断层之间转移位移的断层系统的详细几何形状和滑动历史，以及（3）部署具有足够密度的GPS网络，以区分当前连续变化与不连续变化-日速度场。PI将利用详细的地质测绘、结构分析和GPS大地测量进行综合研究，以解决上述任务。研究人员（Oldow和Satterfield）在该地区都有丰富的工作经验，通过以前的研究，地质测绘和结构分析将建立张性断层系统的区域限制，记录主要和次要断层系统之间的可变几何关系，定义断层运动的运动学历史，并通过记录偏移地貌来对最近的滑动幅度进行一阶估计。结合其他正在进行的或拟议中的研究在中央步行者巷，这项研究的结果应有助于积极transtensional位移转移的一个前所未有的观点，并产生关键的洞察变形运动学的地质和大地测量的比较。

Late Cenozoic deformation is broadly distributed across the North American plate margin of the conterminous western United States and stretches from the San Andreas fault system eastward across the Mojave Desert and into the Basin and Range. The eastern California shear zone and Walker Lane of the western Great Basin form an active belt of structures accommodating about 25% of the relative motion between North America and the Pacific plate. From the Mojave Desert, the displacement is carried north, east of the southern Sierra Nevada, in a narrow zone of deformation bound on the west and east by the Owens Valley and Furnace Creek fault systems. North from the latitude of the central Sierra Nevada, the zone of deformation broadens to include the Walker Lane and centralNevada seismic belt in the northwestern Great Basin. The Sierra Nevada behaves as a coherent tectonic block with a northwest-directed motion of 10-14 mm/yr and forms the western boundary of the zone of distributed deformation in the Great Basin. A complex pattern of active structures underlies west-central Nevada where displacement is transferred from the eastern California shear zone to the Walker Lane and the central Nevada seismic belt. Integrated geologic, seismological, and GPS geodetic results indicate that the central Walker Lane serves as an displacement transfer system linking stepped northwest-trending transcurrent faults. Within the central Walker Lane displacement partitioning is active and may be accommodated by differential motion of tectonic blocks. A GPS velocity field exhibits a systematic increase in magnitude from east to west across the central Walker Lane and is consistent both with block translation and vertical-axis rotation. Zones of divergent, transcurrent, and convergent motion are observed across suspected block boundaries. The observed velocity field is not easily reconciled with the current understanding of fault displacements and points out the difficulty in comparing geodetic and geologic displacement fields.The PI's propose an integrated geodetic and geologic investigation of the central Walker Lane to address two questions: (1) Is displacement transfer between transcurrent structures wholly accommodated by kinematically coordinated slip on throughgoing faults, and (2) are the kinematics of active displacement transfer derived from GPS geodesy consistent with the displacement field estimated by earthquake seismology and fault-slip inversion? The central Walker Lane is ideally suited for this study for three reasons: (1) the region is seismically active and well defined earthquake focal mechanisms exist for the displacement transfer fault system, (2) the faults are well exposed and have produced preliminary fault-slip estimates of deformation kinematics, and (3) a complex present-day displacement field with ~10 mm/yr of differential slip is recorded by a GPS geodetic network. These elements will allow characterization of the kinematics of displacement transfer and offer the opportunity to directly compare different means of measuring deformation kinematics. The PI's primary interest is to characterize the kinematics of deformation in the active displacement transfer stepover and to compare the geodetically determined displacement field with that derived from earthquake focal mechanisms and fault-slip inversion. To achieve their research objectives, several aspects of the extensional stepover system exposed in the central Walker Lane must be examined in greater detail. The primary tasks set out in this project are: (1) to establish the spatial distribution of active high-angle faults linking the bounding transcurrent faults, (2) to document the detailed geometry and slip history of fault systems that transfer displacement between transcurrent faults, and (3) to deploy a GPS network with sufficient density to differentiate between continuous versus discontinuous variations in the present-day velocity field.The PI's will address the tasks listed above with an integrated study utilizing detailed geologic mapping, structural analysis, and GPS geodesy. The investigators (Oldow and Satterfield) each have substantial experience working in the area and by building on previous studies, geological mapping and structural analysis will establish the areal limits of the transtensional fault system, document variable geometric relations between major and secondary fault systems, define the kinematic history of fault motion, and develop first-order estimates of recent slip magnitude by documenting offset landforms. Combined with other ongoing or proposed studies in the central Walker Lane, the results of this research should contribute to an unprecedented view of active transtensional displacement transfer and yield critical insight into the comparison of geologic and geodetic measures of deformation kinematics.