Collaborative Research: 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毗邻的北美板块边缘，从圣安德烈亚斯断裂系统向东延伸，穿过莫哈韦沙漠，进入盆地和山脉。加州东部剪切带和西部大盆地的Walker Lane形成了一条活跃的构造带，容纳了北美和太平洋板块之间约25%的相对运动。从莫哈韦沙漠开始，位移被带到内华达山脉南部以东的北部，在欧文斯山谷和炉溪断层系统的西面和东面交界的狭窄形变带中。形变带从内华达山脉中部的纬度向北扩展，包括大盆地西北部的沃克巷和内华达中部地震带。内华达山脉是一个北西向运动为10-14 mm/a的连贯构造块体，构成了大盆地分布变形带的西部边界。内华达州中西部是一种复杂的活动构造格局，在那里，位移从加利福尼亚州东部的剪切带转移到沃克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，中央沃克巷是一个连接北西向阶梯状横流断裂的位移传递系统。在中央Walker巷内，位移划分是活跃的，并可能被构造块体的差异运动所容纳。在中央Walker巷，GPS速度场表现出自东向西的系统性增大，并与块体平移和垂直轴旋转一致。在可疑的块体边界上观察到发散、横流和收敛运动的区域。观测到的速度场不容易与目前对断层位移的理解相一致，并指出了比较大地测量位移场和地质位移场的困难。PI建议对中央Walker巷进行综合大地测量和地质调查，以解决两个问题：(1)横流构造之间的位移传递是否完全由贯穿断层上的运动学协调滑动来调节；(2)GPS大地测量得出的活动位移传递的运动学与地震地震学和断层滑动反演估计的位移场是否一致？中央Walker Lane非常适合于这项研究，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大地网记录了约10 mm/年的复杂现代位移场。这些元素将允许表征位移传递的运动学，并提供直接比较测量变形运动学的不同方法的机会。PI的主要兴趣是描述活动位移传递跨越中的形变运动学，并将大地测量确定的位移场与地震震源机制和断层滑动反演得到的位移场进行比较。为了实现他们的研究目标，必须更详细地研究暴露在中央步行道上的伸展跨越式系统的几个方面。该项目的主要任务是：(1)建立连接边界横流断层的高角度活动断层的空间分布，(2)记录在横流断层之间传递位移的断层系统的详细几何和滑动历史，以及(3)部署具有足够密度的GPS网络，以区分当今速度场中的连续和不连续变化。PI将通过利用详细的地质制图、构造分析和GPS大地测量进行综合研究来解决上述任务。调查人员(Oldow和Satterfield)都有在该地区工作的丰富经验，通过在以前研究的基础上，地质制图和构造分析将确定伸展断裂系统的区域界限，记录主要和次要断裂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对最近滑动强度进行一级估计。与中央Walker Lane正在进行或计划进行的其他研究相结合，这项研究的结果应该有助于以一种前所未有的观点看待活动的扭张性位移转移，并对形变运动学的地质和大地测量措施的比较产生关键的洞察。

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.