SGER: Lake Sediment Cores and Surface Exposure Dates Near the Epicenter of the 1872 Washington Earthquake

1872年华盛顿州发生的地震是太平洋西北地区已知最大的地壳地震，估计震级超过了美国最近发生的破坏性地震。引起1872年地震的断层是未知的，更早的地震也没有记录。最近对现代地震精确重新定位的研究追踪了1872年华盛顿切兰湖附近假定的震中区域的一次盲冲。初步的地图显示，哥伦比亚河沿岸可观察到的冰川梯田变形可能与1872年有关。这个项目正在探索两个假设。首先，1872年的地震是由一个向西北方向的盲冲断层（由震源重新定位所描绘）的滑动引起的，该断层在奥卡诺根汇合处和韦纳奇市之间沿哥伦比亚河谷的冰川沉积物的地形偏转中产生了一个广泛的褶皱。对阶地表面进行测绘和详细的GPS测量，再加上地表暴露测年方法，正用于验证这一假设。其次，地面震动导致了车兰湖和附近其他湖泊的沉积物变形。较早的事件记录在较低地层层位类似的变形。目前正在从切兰湖收集岩心，以确定是否存在与1872年事件有关的变形，并在地层剖面较低的地方寻找早期大地震的证据。

he 1872 Washington State earthquake is the largest known crustal earthquake in the Pacific Northwest, with an estimated magnitude exceeding most recent damaging U.S. earthquakes. The fault that produced the 1872 earthquake is not known, nor has a record of earlier events been produced. Recent work on the precise relocation of modern earthquakes traces a blind thrust in the presumed 1872 epicentral region around Lake Chelan, Washington. Preliminary mapping suggests observable deformation of glacial terraces along the Columbia River that may be associated with the 1872. This project is exploring two hypotheses. First, The 1872 earthquake was produced by slip on a northwest-striking, blind thrust (delineated by hypocenter relocation) that produced a broad fold visible in the topographic deflection of glacial deposits along the Columbia River valley between the Okanogan confluence and the city of Wenatchee. Mapping and detailed GPS surveying of the terrace surfaces coupled with surface exposure dating methods are being used to test this hypothesis. Second, ground shaking caused deformation of sediments in Lake Chelan and other near-by lakes. Earlier events are recorded by similar deformation at lower stratigraphic horizons. Cores are being collected from Lake Chelan to determine if deformation related to the 1872-event is present and to seek evidence for earlier large earthquakes, lower in the stratigraphic section.