Megathrust Paleogeodesy at the Central Cascadia Subduction Zone

卡斯卡迪亚俯冲带河口周围的湿地沉积物记录了过去5000年来板块边界地震的独特记录。然而，卡斯卡迪亚过去对陆地水平变化的测量精度较低(误差大于正负0.5米)，测量空间有限，只涵盖俯冲带应变积累和释放的完整周期的一小部分。这使得过去的测量不足以确定哪些板块边界变形的假设是最有效的。通过将最近发展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，如有孔虫和硅藻，这一缺陷将得到纠正。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，并将结果用于改进我们基于微化石的转移函数。传递函数被应用于几个河口的有孔虫和硅藻化石数据，以重建跨越卡斯卡迪亚俯冲带中部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和河口沉积物的放射性碳测年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。我们重建的改进的垂直分辨率将：(1)产生更精确的卡斯卡迪亚10至100年时间段的形变测量；(2)为大地震前相互矛盾的沿海隆起与沉降假说提供关键测试；(3)有助于约束卡斯卡迪亚板块-边界变形的区域模型；以及(4)直接测试为其他俯冲带提出的滑动可预测、时间可预测和滑动时间不可预测应变累积的假设。

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.