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了解有限。对断层作用的基本理解需要详细描述岩体和结构的几何形状，以及它们在断层带内和附近的运动。该项目通过定义圣安德烈亚斯断层沿线主要岩体的位置、产状和特征，并确定与断裂带主要结构相关的活动变形速率，为加州中南部圣安德烈亚斯断层大量使用仪器和地球物理成像的帕克菲尔德段提供了这样的解释。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走滑断裂带沿线地貌发育、走滑断裂带内部和邻近地壳中块体的运动以及这一重要断裂带内和邻近地质史所定义的物质性质等问题很有价值。此外，这些数据和推断对于全面了解地球范围元素：圣安德烈亚斯深部断层观测站(SAFOD)的结果至关重要。目前正在进行SAFOD半径10公里范围内的地质和地貌测绘(1：6000或更大比例尺)。在较低但仍相对详细的比例尺(1：24000或更高)上，正在绘制帕克菲尔德地区的选定部分的地图，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岩样品的磷灰石裂变径迹研究，可以推断该地区的折返和岩石抬升历史。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，包括主圣安德烈亚斯断层、副走滑断层以及附近的倾滑断层和褶皱。这种构造可以通过它们对地貌和年轻沉积物的破坏来识别，通过对与它们相关的变形的区域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水系的阶地时间序列，确定沿活动构造的形变速率，以及改善古地震记录。与滑坡有关的运移速率正在与根据磷灰石裂变径迹热年代学推断的相同区块的挖掘速率进行比较。地质和地貌测绘结果以及遥感图像将汇编在一个数字地理空间数据系统中。

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.