Kilometer-Scale Fault Zone Structure and Kinematics Along the San Andreas Fault near Parkfield, California

由于城市不断向地震多发地区发展，地震对全球社会的威胁越来越大，但我们对地震行为的理解有限。对断层的基本理解需要对岩体和构造的几何形状及其在断层带内和断层带附近的运动进行详细的描述。该项目为加利福尼亚中南部的圣安德烈亚斯断层帕克菲尔德部分的大量仪器和地球物理成像提供了这种解释。通过确定沿圣安德烈亚斯断层的主要岩体的位置、姿态和特征，并确定与断裂带主要结构相关的活动变形率。详细的地质和地貌数据集以及几何和运动学模型对于解决与沿走滑断裂带的景观发展、走滑断裂带内部和邻近的上地壳块体运动以及该重要断裂带内部和邻近的地质历史所定义的物质特性有关的问题是有价值的。此外，数据和推断对于完全理解EarthScope元素：圣安德烈亚斯断层观测站（SAFOD）的结果是必不可少的。目前正在SAFOD半径10公里范围内进行地质和地貌测绘（1:6000或更大比例）。在较低但仍然相对详细的比尺（1:24000或更大），帕克菲尔德地区的选定部分正在绘制地图，以加强对构造地质、地貌和地质年代学数据的解释。通过对第三系沉积岩和花岗质岩样品的磷灰石裂变径迹研究，可以推断该地区的发掘和岩石隆升历史。地貌分析有助于记录该地区活动地质构造的几何形状和速率，包括主要的圣安德烈亚斯断层、次级走滑断层以及附近的倾滑断层和褶皱。这些构造可以通过它们对地貌和年轻沉积物的破坏来识别，并通过对与它们相关的变形的面积分布的解释来推断它们的几何形状。这些研究包括建立该地区主要排水系统的阶地时序，确定沿活动构造的变形速率，以及改进古地震记录。将与滑坡有关的搬运速率与根据磷灰石裂变径迹热年代学推断的同一块体的掘出速率进行比较。地质地貌填图成果和遥感影像将在数字地理空间数据系统中编制。

Earthquakes are an increasing threat to societies globally because of continued urban development into earthquake-prone areas, yet our understanding of earthquake behavior is limited. Fundamental understanding of faulting requires detailed description of the geometry of rock bodies and structures and their motions within and adjacent to fault zones. This project is providing such an explanation for the heavily instrumented and geophysically-imaged Parkfield section of the San Andreas Fault in south-central California.by defining the positions, attitudes, and characteristics of the major rock bodies along the San Andreas Fault, and determining the rates of active deformation associated with the principal structures of the fault zone. The detailed geologic and geomorphic data sets and geometric and kinematic models are valuable for addressing questions related to landscape development along strike-slip fault zones, the motions of blocks in the upper crust within and adjacent to strike-slip fault zones, and the material properties as defined by geologic history within and adjacent to this important fault zone. In addition, the data and inferences are essential for a complete understanding of the results from the EarthScope element: San Andreas Fault Observatory at Depth (SAFOD).Geologic and geomorphic mapping (1:6000 scale or greater) in an area within a 10 km radius of SAFOD is being performed. At a lower but still relatively detailed scale (1:24000 or greater), selected portions of the Parkfield region are being mapped to enhance interpretations of the structural geology, geomorphic, and geochronologic data. An apatite fission track study on samples from the Tertiary sedimentary rocks and the granitic rocks permits inference of the exhumation and rock uplift history for the area. The geomorphic analyses help document the geometries and rates of active geologic structures in the area, including the main San Andreas Fault, subsidiary strike-slip faults, and nearby dip-slip faults and folds. Such structures may be identified by their disruption of landforms and young deposits, and their geometries inferred by interpretation of the areal distribution of deformation associated with them. These investigations include establishing a terrace chronosequence for the major drainage system of the area, determining rates of deformation along the active tectonic structures, and improving the paleoseismic record. Rates of transport associated with landslides are being compared with exhumation rates inferred for the same blocks based on the apatite fission track thermochronology. The geologic and geomorphic mapping results and remotely sensed imagery will be compiled in a digital geospatial data system.