Investigating the long-term record of seismically induced erosion preserved in the stratigraphy of Lake Quinault, Washington

在这个项目中，将调查位于华盛顿奥林匹克半岛上的一个深冰碛湖--奎诺特湖沉积物填充物中的卡斯卡迪亚大地震的长期记录。 奎诺特湖的地理位置非常理想，可以提供卡斯卡迪亚地震活动及其高地流域规模影响的长期记录。 将进行一次高分辨率地震反射勘测，以提供关于湖泊沉积物填充物厚度和总体几何形状的信息，并查明可能在过去几千年的地震事件中触发的湖缘滑塌沉积物。 长（ca.将从盆地中心附近的至少五个位置采集12米）的活塞岩心，并使用岩心描述、地球物理测量和X射线照相术识别和解释事件层。 这些层将与湖缘地层学相关，以帮助建立其同震起源，宏观植物碎片的放射性碳分析将用于评估其与一个完善的区域古地震历史的关系。 沉积物的地球化学分析将进行测试的假设，一个大的俯冲带地震后，深基岩滑坡的沉积物的生产将压倒侵蚀通过近地表机制在十年的时间尺度。 由于他们的假设更大的深度从地表以下的起源，我们预测，相比于其他地层，有机质和沉积物积累在奎诺特湖后立即大地震，并持续几年将相对耗尽同位素，包括14 C，10 Be，和26铝，将有相对较高的26铝/10 Be的比率。 该项目的目标是提高对北美卡斯卡迪亚边缘大俯冲或其他大地震的陆地高地反应的理解。 以前对沉降的沿海低地土壤、低洼的沿海湖泊和泻湖、峡湾和深海浊积岩的研究已经确定，这些事件在该地区以300-500年的频率发生。 根据对世界上地形起伏较大的其他地区的研究，地震引发的山体滑坡可能是未来事件发生期间和之后立即面临的对生命和基础设施的最重大危害之一。 通过记录过去数千年来重复地震引发的山体滑坡的沉积和地球化学记录，这项研究将深入了解未来事件对河流和沿海环境沉积物供应的潜在十年级影响，并对淡水和咸水生态系统产生影响。 我们的研究结果将为太平洋西北地区的利益相关者提供重要信息，包括对该湖拥有管辖权的奎诺特印第安民族（QIN），并将开发用于评估其他地区地震灾害的工具。 此外，我们的研究将有助于阐明与大地震相关的滑坡和其他质量浪费过程在卡斯卡迪亚和其他俯冲边缘以上的地形演变中所起的作用。

In this project the long-term record of large Cascadia earthquakes contained in the sedimentary fill of Lake Quinault, a deep, glacial moraine-dammed lake on the Olympic Peninsula, Washington, will be investigated. Lake Quinault is ideally situated to provide a long record of both seismicity in Cascadia and its upland drainage-basin scale impacts. A high resolution seismic reflection survey will be conducted to provide information about the thickness and overall geometry of the lake's sedimentary infill and to identify lake-margin slump deposits that may have been triggered during earthquake events over the past several thousand years. Long (ca. 12 m) piston cores will be recovered from at least five locations near the basin center, and event layers will be identified and interpreted using core descriptions, geophysical measurements, and x-radiography. The layers will be correlated to the lake-margin stratigraphy to help establish their co-seismic origin, and radiocarbon analyses of macroscopic plant debris will be used to evaluate their relationships to a well-established regional paleo-seismological history. Geochemical analyses of the sediments will be performed to test the hypothesis that following a great subduction zone earthquake, the production of sediment by deep-seated bedrock landslides will overwhelm erosion via nearer-surface mechanisms on a decadal time scale. Because of their hypothesized greater depth of origin from beneath the surface, we predict that compared to other strata, the organic matter and sediments accumulating in Lake Quinault immediately after a large earthquake and continuing for several years will be relatively depleted in isotopes including 14C, 10Be, and 26Al and will have relatively higher 26Al/10Be ratios. The goal of this project is to improve understanding of the terrestrial upland response to great subduction or other large earthquakes on the Cascadia margin of North America. Previous studies of subsided coastal lowland soils, low-lying coastal lakes and lagoons, fjords, and deep sea turbidites have established that these events have occurred in this region at 300-500 year frequencies. Based on research in other areas of the world with large topographic relief, earthquake-triggered landslides are likely to be one of the most significant hazards to life and infrastructure faced during and in the immediate aftermath of future events. By documenting the sedimentary and geochemical record of landslides triggered by repeated earthquakes spaced over the past thousands of years, this study will offer insight into potential decadal-scale impacts of future events on sediment supply to riverine and coastal environments, with implications for both fresh and salt water ecosystems. Our results will provide important information for stakeholders in the Pacific Northwest, including the Quinault Indian Nation (QIN), who have jurisdiction over the lake, and will develop tools for assessing earthquake hazards in other regions. Our study, moreover, will help to elucidate the role that landslides and other mass wasting processes associated with large earthquakes have played in the evolution of topography above Cascadia and other subduction margins over millennial time scales.