Megathrust Paleogeodesy at the Central Cascadia Subduction Zone

卡斯卡迪亚中部俯冲带的巨型逆冲古地质测量

• 批准号: 0842728
• 负责人: Benjamin Horton
• 金额: $ 23.31万
• 依托单位: University of Pennsylvania
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-02-15 至 2013-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0842728&HistoricalAwards=false
• 关键词: Megathrust; Paleogeodesy; Central; Cascadia; Subduction

The wetland sediments fringing estuaries at the Cascadia subduction zone harbor a unique record of plate-boundary earthquakes during the past 5,000 years. However, the precision of past measurements of land-level changes at Cascadia is low (errors of greater than plus or minus 0.5 meter), the measurements are spatially limited, and they span only fractions of complete cycles of subduction zone strain accumulation and release. This makes past measurements insufficient for determining which hypotheses of plate-boundary deformation are most valid. This deficiency will be redressed by applying recently developed statistical transfer functions to microfossils, such as foraminifera and diatoms, collected from Cascadia estuarine sediments. Similar studies of sea-level change on other continents have obtained an unprecedented vertical resolution of plus or minus 0.1-0.3 meter. Seasonal and spatial differences in modern foraminfera and diatoms from Cascadia estuaries are assessed and the results are used to improve our microfossil-based transfer functions. Transfer functions are applied to fossil foraminiferal and diatom data at several estuaries to reconstruct land-level changes spanning the four most recent great earthquake cycles in the central Cascadia subduction zone. Detailed lithostratigraphical and biostratigraphical descriptions and radiocarbon dating of estuarine sediment allow correlation of microfossil reconstructions among estuaries and help reconstruct a history of plate-boundary deformation in Oregon. The improved vertical resolution of our reconstructions will: (1) yield more precise measures of Cascadia deformation over time periods of 10 to 100 years; (2) provide critical tests for competing hypotheses of coastal uplift versus subsidence just prior to great earthquakes; (3) help constrain regional models of Cascadia plate-boundary deformation; and (4) directly test hypotheses of slip-predictable, time-predictable, and slip-time-unpredictable strain accumulation proposed for other subduction zones.

卡斯卡迪亚俯冲带河口边缘的湿地沉积物保​​存着过去 5000 年来板块边界地震的独特记录。然而，过去对卡斯卡迪亚陆地平面变化的测量精度较低（误差大于正负0.5米），测量受到空间限制，并且仅涵盖俯冲带应变积累和释放的完整周期的一部分。这使得过去的测量不足以确定哪些板块边界变形的假设最有效。通过将最近开发的统计传递函数应用于从卡斯卡迪亚河口沉积物收集的有孔虫和硅藻等微化石，可以弥补这一缺陷。其他大陆海平面变化的类似研究获得了前所未有的正负0.1-0.3米的垂直分辨率。对来自卡斯卡迪亚河口的现代有孔虫和硅藻的季节和空间差异进行了评估，并将结果用于改善我们基于微化石的传递函数。将传递函数应用于几个河口的化石有孔虫和硅藻数据，以重建卡斯卡迪亚中部俯冲带最近四个大地震周期的土地平面变化。详细的岩石地层和生物地层描述以及河口沉积物的放射性碳测年可以对河口之间的微化石重建进行关联，并有助于重建俄勒冈州板块边界变形的历史。我们重建的垂直分辨率的提高将：（1）在 10 到 100 年的时间段内产生更精确的卡斯卡迪亚变形测量； (2) 为大地震前海岸隆起与下沉的竞争假设提供关键检验； （3）有助于约束卡斯卡迪亚板块边界变形的区域模型； (4)直接检验针对其他俯冲带提出的滑移可预测、时间可预测和滑移时间不可预测的应变积累假设。