Holocene tectonics and fault reactivation in the foothills of the north Cascade Mountains, Washington
Holocene tectonics and fault reactivation in the foothills of the north Cascade Mountains, Washington
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华盛顿州喀斯喀特山脉北部山麓的全新世构造和断层再活动
DOI：
10.1130/ges00880.1
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发表时间：
2013
期刊：
影响因子：
2.5
通讯作者：
Timothy L. Hyatt
中科院分区：
文献类型：
--
作者：
B. Sherrod;E. Barnett;E. Schermer;H. Kelsey;J. F. Hughes;F. Foit;C. Weaver;R. Haugerud;Timothy L. Hyatt
我们使用激光雷达图像，以确定最新更新世冰川沉积物沿着北福克Nooksack河Whatcom县，华盛顿（美国）的两个断层陡坎。对这些以前未知的陡坎的绘图和古地震调查提供了对北方普吉特低地地震历史和地震危险性的限制。肯德尔陡崖沿着博尔德溪断层（南倾的第三纪正断层）的测绘轨迹，而峡谷溪陡崖紧邻南倾的峡谷溪断层和南倾的冰川伸展断层。这两个悬崖都是南面朝上，与附近基岩断层上观察到的位移方向相反。在这些陡崖上挖掘的沟渠暴露了褶皱和断层的第四纪晚期冰川沉积物，当地的日期为约100年至约100年。12和13 ka，全新世埋藏土和陡崖崩积层。反向和斜断层的土壤和崩积物表明至少有两个晚全新世地震，而折叠的冰川水洗形成之前的冰后期土壤表明一个更早的全新世地震。在峡谷溪开挖中，断层两侧床层厚度的突然变化表明存在滑动的横向分量。在湿地附近的肯德尔陡崖的沉积物记录三个池塘形成的情节在全新世，我们推断，表面破裂的博尔德溪故障在过去的地震暂时堵塞了河道，创造了一个短暂的湖泊。博尔德溪和峡谷溪断层形成于第三纪早期至中期，为正断层，可能处于休眠状态，直到在新的应力状态下重新激活为逆断层。最近的地震-每一个可能M w > 6.3和约会约。8050-7250日历年B. P.（cal yr B. P.），3190-2980 cal. yr B.P.，和910-740 cal. yr B.P.-证明了北方普吉特低地的逆断层对西雅图（华盛顿）和温哥华、不列颠哥伦比亚省（加拿大）之间的城市地区构成了危险。
We use LiDAR imagery to identify two fault scarps on latest Pleistocene glacial outwash deposits along the North Fork Nooksack River in Whatcom County, Washington (United States). Mapping and paleoseismic investigation of these previously unknown scarps provide constraints on the earthquake history and seismic hazard in the northern Puget Lowland. The Kendall scarp lies along the mapped trace of the Boulder Creek fault, a south-dipping Tertiary normal fault, and the Canyon Creek scarp lies in close proximity to the south-dipping Canyon Creek fault and the south-dipping Glacier Extensional fault. Both scarps are south-side-up, opposite the sense of displacement observed on the nearby bedrock faults. Trenches excavated across these scarps exposed folded and faulted late Quaternary glacial outwash, locally dated between ca. 12 and 13 ka, and Holocene buried soils and scarp colluvium. Reverse and oblique faulting of the soils and colluvial deposits indicates at least two late Holocene earthquakes, while folding of the glacial outwash prior to formation of the post-glacial soil suggests an earlier Holocene earthquake. Abrupt changes in bed thickness across faults in the Canyon Creek excavation suggest a lateral component of slip. Sediments in a wetland adjacent to the Kendall scarp record three pond-forming episodes during the Holocene—we infer that surface ruptures on the Boulder Creek fault during past earthquakes temporarily blocked the stream channel and created an ephemeral lake. The Boulder Creek and Canyon Creek faults formed in the early to mid-Tertiary as normal faults and likely lay dormant until reactivated as reverse faults in a new stress regime. The most recent earthquakes—each likely M w > 6.3 and dating to ca. 8050–7250 calendar years B.P. (cal yr B.P.), 3190–2980 cal. yr B.P., and 910–740 cal. yr B.P.—demonstrate that reverse faulting in the northern Puget Lowland poses a hazard to urban areas between Seattle (Washington) and Vancouver, British Columbia (Canada).