Megathrust Paleogeodesy at the Central Cascadia Subduction Zone

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，过去对卡斯卡迪亚地区陆面变化的测量精度较低（误差大于±0.5米），测量结果空间有限，而且它们只涵盖了俯冲带应变积累和释放完整旋回的一小部分。这使得过去的测量不足以确定哪种关于板块边界变形的假设是最有效的。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中收集的微化石，例如有孔虫和硅藻，可以纠正这一缺陷。对其他大陆海平面变化的类似研究已经获得了前所未有的正负0.1-0.3米的垂直分辨率。对卡斯卡迪亚河口现代有孔虫和硅藻的季节和空间差异进行了评估，并将结果用于改进基于微化石的传递函数。将传递函数应用于几个河口的有孔虫和硅藻化石数据，以重建中部卡斯卡迪亚俯冲带最近四个大地震旋回的陆地水平变化。详细的岩石地层学和生物地层学描述以及河口沉积物的放射性碳定年可以使河口之间的微化石重建相互关联，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年的时间内对卡斯卡迪亚的变形进行更精确的测量；(2)为大地震前海岸隆起与下沉的相互竞争的假设提供关键的检验；(3)有助于约束喀斯喀迪亚板块边界变形的区域模式；(4)直接验证其他俯冲带的滑动可预测、时间可预测和滑动不可预测应变积累假设。

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.