Electron spin resonance plateau dating of periodicity of activity on the San Gabriel fault zone, southern California
Electron spin resonance plateau dating of periodicity of activity on the San Gabriel fault zone, southern California
复制标题
南加州圣盖博断层带活动周期的电子自旋共振平台测年
DOI：
--
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
H. Schwarcz
中科院分区：
文献类型：
--
作者：
Hee;H. Schwarcz
我们使用电子自旋共振（ESR）高原测年方法研究了南加州小图洪加地区圣盖博断层带第四纪断层活动的时空模式。小图洪加地区发育两个主要断层带（圣盖博和圣苏珊娜-马德雷山脉）和褶皱。圣苏珊娜-马德雷断裂带的逆冲断层和褶皱痕迹与圣盖博断裂带大致平行，表明最大水平应力几乎垂直于圣盖博断裂带。圣盖博断层带主股的弯曲产生了局部压压区域，并将最大水平应力的方向改变为与主股成较小的角度，导致与断层主走向倾斜的副断层和褶皱的发育。这些结构特征可以通过低阻力解耦剪切与压变相结合的过程来解释。 Little Tujunga 地区挤压变形和走滑变形划分的时间模式尚不清楚。主断层和次断层的 ESR 日期范围为 1970 年 11 月至 40 ka。这些日期显示了活动期和非活动期的时间聚类，类似于历史和全新世地震断层活动中所见的情况。在给定的活动期内，断层活动沿着圣盖博断层带的约束弯曲广泛分布。历史地震断层同样表明，断层应变在抑制弯曲方面受到禁止，断层活动扩展至距主链数公里处。一些断层被重新激活，在主断层岩石的旧带内产生了明确的重新活动断层泥带，其显示出比主断层岩石更年轻的ESR日期。圣盖博断层带以前被认为是圣安德烈亚斯断层系统中挖掘出的古老断层。这项研究的结果表明，虽然比圣安德烈亚斯断层带的活动性要低得多（Pallett Creek 的平均复发间隔为 132 年），但圣盖博断层带的长期（80-120 k.y.）循环断层活动持续到更新世。这些结果表明，ESR测年可用于评估古地震断层运动的复发间隔和地壳稳定性，时间分辨率为5%~10%。
We investigated temporal and spatial patterns of Quaternary fault activity of the San Gabriel fault zone in the Little Tujunga region, southern California, using the electron spin resonance (ESR) plateau dating method. Two major fault zones (San Gabriel and Santa Susana–Sierra Madre) and folds are developed in the Little Tujunga region. The traces of thrust faults and folds of the Santa Susana–Sierra Madre fault zone are roughly parallel to the San Gabriel fault zone, indicating that the maximum horizontal stress was nearly perpendicular to the San Gabriel fault zone. Bends in the main strands of the San Gabriel fault zone yielded local transpressive regimes and changed the direction of maximum horizontal stress to a lower angle to the main strands, resulting in the development of subsidiary faults and folds oblique to the main trend of the fault. These structural features can be explained by the process of low drag-decoupled shear combined with transpression. The temporal pattern of partition between compressional and strike-slip deformation in the Little Tujunga region is not clear yet. ESR dates from both the main strands and subsidiary faults range from November 1970 to 40 ka. The dates show temporal clustering into active and inactive periods, analogous to those seen in historic and Holocene earthquake fault activity. Within a given active period, fault activity is widely distributed along a restraining bend in the San Gabriel fault zone. Historic earthquake faults similarly show that fault strain was prohibited in restraining bends and that fault activities spread out up to several kilometers away from the main strand. Some faults were reactivated, producing well-defined bands of reactivated fault gouge within old zones of host fault rock, which exhibit younger ESR dates than those of the host fault rocks. The San Gabriel fault zone was formerly considered to be an exhumed ancient fault of the San Andreas fault system. Results from this study suggest that, although much less active than the San Andreas fault zone (average recurrence interval in Pallett Creek, 132 yr), the long-term (80–120 k.y.) cyclic fault activity of the San Gabriel fault zone continued into the Pleistocene. These results show that ESR dating can be used to evaluate the recurrence intervals of paleoearthquake fault movements and crustal stability with a temporal resolution of 5%–10%.