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

1872年华盛顿州地震是太平洋西北地区已知的最大地壳地震，估计震级超过了美国最近发生的破坏性地震。引发1872年地震的断层尚不清楚，也没有更早事件的记录。最近关于现代地震精确定位的研究发现，在华盛顿州车兰湖周围假定的1872年震中区域存在盲目推力。初步测绘表明，哥伦比亚河沿岸的冰川阶地出现了明显的变形，这可能与1872年的冰川事件有关。这个项目正在探索两个假设。首先，1872年的地震是由向西北方向的盲目推覆(由震中重新定位划定)的滑移造成的，在奥卡诺根交汇处和韦纳奇市之间的哥伦比亚河河谷冰川沉积的地形偏转中可以看到一个宽阔的褶皱。对梯田表面的测绘和详细的GPS测量，加上表面暴露测年方法，正在被用来检验这一假设。其次，地面震动导致车兰湖和附近其他湖泊的沉积物变形。较早的事件在较低的地层层位通过类似的变形被记录下来。正在从车兰湖采集岩芯，以确定是否存在与1872年事件有关的变形，并寻找地层剖面较低的早期大地震的证据。

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.