Using vertical axis rotations to characterize off-fault deformation across the San Andreas fault system, central California
Using vertical axis rotations to characterize off-fault deformation across the San Andreas fault system, central California
复制标题
使用垂直轴旋转来表征加利福尼亚州中部圣安德烈亚斯断层系统的断层变形
作者：
S. Titus;S. Crump;Z. Mcguire;E. Horsman;B. Housen
我们使用新的古地磁数据的垂直轴旋转，以限制在圣安德烈亚斯断层系统在加州中部的断层变形。样品收集自177个地点的中新世蒙特利组毗邻林科纳达断层。来自57个地点的可靠方法有3个突出的模式：（1）最大的顺时针旋转靠近林科纳达和纳西米恩托断层;（2）在圣安德烈亚斯断层附近没有观察到明显的旋转;（3）在帕索罗伯斯西北部的几个地点观察到逆时针旋转。这些古地磁结果进行比较，其他两个措施的断层外变形旋转可以计算。从褶皱为基础的运动学模型的结果表明，增加顺时针旋转对林科纳达故障，与模式1一致。在圣安德烈亚斯断层附近的Salinian基底上的岩石中观察到很少的褶皱，这表明几乎没有发生变形，并为模式2中可以忽略的古地磁旋转提供了解释。从全球定位系统速度场计算的旋转预测逆时针旋转与模式3中从古地磁数据观察到的旋转一致。速度场中的广泛模式似乎受到沿圣安德烈亚斯断层从蠕动到锁定行为沿着的过渡的控制，逆时针旋转的区域与这种过渡有关。因此，我们认为，蠕动段已asependently地质时间尺度，以产生所观察到的古地磁旋转。所有三个数据集的整合表明，圣安德烈亚斯断层边界记录了地质和大地测量时间尺度上断层平行板块运动的重要组成部分。
We use vertical axis rotations from new paleomagnetic data to constrain off-fault deformation within the San Andreas fault system in central California. Samples were collected from 177 sites in the Miocene Monterey Formation adjacent to the Rinconada fault. Reliable means from 57 sites have 3 prominent patterns: (1) the largest clockwise rotations are close to the Rinconada and Nacimiento faults; (2) no significant rotation is observed near the San Andreas fault; and (3) counterclockwise rotations are observed at several sites northwest of Paso Robles. These paleomagnetic results are compared to two other measures of off-fault deformation where rotation can be calculated. Results from a fold-based kinematic model show increasing clockwise rotations toward the Rinconada fault, consistent with pattern 1. Few folds are observed in rocks on Salinian basement near the San Andreas fault, suggesting that little deformation has occurred, and providing an explanation for the negligible paleomagnetic rotations in pattern 2. Rotations calculated from the global positioning system velocity field predict counterclockwise rotations that coincide with those observed from paleomagnetic data in pattern 3. Broad patterns in the velocity field appear to be controlled by the transition from creeping to locked behavior along the San Andreas fault, and the region of counterclockwise rotation is linked to this transition. Thus, we suggest that the creeping segment has been aseismic over geologic time scales in order to produce the observed paleomagnetic rotations. The integration of all three data sets demonstrates that the San Andreas fault borderlands record an important portion of fault-parallel plate motion over geologic and geodetic time scales.