Large-magnitude earthquakes and hydrologic events in mountainous settings commonly trigger thousands of landslides, and slope failures typically constitute a significant proportion of the damage associated with these events. Large, dormant deep-seated landslides are ubiquitous in the Oregon Coast Range, western United States, yet a method for calculating landslide ages with the precision required to diagnose a specific triggering event, including the A.D. 1700 Cascadia earthquake, has remained elusive. Establishing a compelling connection between prehistoric slope instability and specific triggers requires landslide ages with precision greater than that provided by 14C dating of detrital materials. Tree-ring analysis is the only known method capable of determining landslide age with this precision. Dozens of landslide-dammed lakes in western Oregon present an opportunity to use tree rings from drowned snags, or “ghost forests,” to establish the year of death, and thus landsliding. We cross-dated tree-ring indices from drowned Douglas fir trees with live tree-ring records from the Oregon Coast Range that exhibit synchronous, time-specific patterns due to regional climate variations. Our analyses determined that the landslides responsible for creating Wasson and Klickitat Lakes occurred in A.D. 1819 and 1751, respectively. The 14C dates from selected tree rings and landslide deposit detritus are consistent with our tree-ring analysis, although the ages exhibit high variability, revealing the limitations of using 14C dating alone. Because dendrochronology provides annual precision for landsliding, sampling of tree rings at additional landslide-dammed lakes throughout the Oregon Coast Range can be used to constrain the potential effects of ground motion and major storms on Cascadia landscapes.

中文翻译：

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俄勒冈州西部滑坡的年代测年：寻找卡斯卡迪亚公元1700年地震的信号

山区的大地震和水文事件通常会引发数千次滑坡，而斜坡破坏通常在与这些事件相关的破坏中占很大比例。在美国西部的俄勒冈州海岸山脉，普遍存在着休眠的大型深部滑坡，然而，以精确的速度来计算滑坡年龄的方法仍然难以捉摸，而这种滑坡年龄是诊断特定触发事件所需的精度，包括公元1700年卡斯卡迪亚地震。在史前斜坡失稳与特定触发因素之间建立令人信服的联系，需要的滑坡年龄要比14C碎屑物质测年的精度更高。树木年轮分析是能够以这种精度确定滑坡年龄的唯一已知方法。俄勒冈州西部数十个滑坡筑坝的湖泊为人们提供了机会，利用淹没的断枝或“鬼林”中的树木年轮来确定死亡年份，并因此发生滑坡。我们将淹没的道格拉斯杉树的树年轮值与俄勒冈州海岸山脉的活树年轮记录进行了过时交合，这些记录由于区域气候变化而呈现出特定时间的同步模式。我们的分析确定，造成沃森湖和克利基塔特湖的滑坡分别发生在公元1819年和1751年。来自选定树木年轮和滑坡沉积物碎屑的14 C日期与我们的树木年轮分析一致，尽管年龄显示出较高的可变性，这揭示了仅使用14 C日期的局限性。由于树状年代学可以提供每年一次的滑坡精度，