Imaging Fine-scale Density Structure in the Ocean with Seismic Reflection Data

最近的研究表明，不同密度的水团之间的边界会产生反射，这些反射可以在最初为对海底下的结构成像而采集的地震数据中观察到。由于地震反射数据是在过去几十年里在世界各地的海洋中收集的，它们提供了一个机会来扩大对各种海洋过程的空间和时间限制。建议检查自20世纪80年代中期以来沿美国西部大陆边缘收集的大量地震反射数据库，这些数据库最初是为了研究与门多西诺转换断层和卡斯卡迪亚俯冲带有关的构造过程而获得的。一个目标是分析在门多西诺断裂带东端观测到的密度场的局部扰动，以检验它们是由潮汐诱导的混合产生的假设。来自底部混合层顶部的可能反射也可能与内波与陡壁侧翼海底的相互作用有关。另一个目标是确定加州暗流中涡旋强度和分布的时间和空间变化。这些漩涡已经被漂流者探测到，并在1997年至2003年作为NSF/NOAA GLOBEC计划的一部分在俄勒冈州和加利福尼亚州北部近海获得的广泛的水文数据库中表现明显。由于水文和地震数据在时间和空间上重叠，因此有机会测试从地震数据得出的海洋密度模型的有效性，并绘制过去没有其他数据这样做的时候的涡旋空间范围，从而扩大历史记录。将需要重新处理和反演，以优化对海洋的精细速度/密度结构的成像；大多数现有数据都是使用扭曲并往往消除源自海洋而不是海底之下的信号的参数进行处理的。洋流体制的变化对生态和气候有广泛的影响。该项目还将为一名研究生提供在地球物理学中具有广泛适用性的数字信号处理技术方面的培训。最后，这些成果将用于在当地学校和其他旨在传播地球科学和海洋学的重要性和激动人心的论坛上由私人投资机构进行的公开演讲。

Recent studies have shown that boundaries between water masses of different density result in reflections that can be observed in seismic data originally acquired to image the structure beneath the seafloor. Because seismic reflection data have been collected throughout the world oceans over past several decades, they provide an opportunity to extend spatial and temporal constraints on a variety of ocean processes. It is proposed to examine the extensive seismic reflection database collected since the mid-1980s along the continental margin of the western US, which were originally acquired to study tectonic processes associated with the Mendocino transform fault and Cascadia subduction zone. One objective is to analyze local perturbations of the density field that are observed over the eastern end of the Mendocino Escarpment to test the hypothesis that they result from tidally induced mixing. A possible reflection from the top of a bottom mixed layer may also be associated with interaction of internal waves with the seafloor on the flank of the Escarpment. Another objective is to determine temporal and spatial variations in the strength and distribution of eddies in the California undercurrent. These eddies have been detected by drifters and are apparent in the extensive hydrographic data base acquired offshore Oregon and northern California between 1997 and 2003 as part of the NSF/NOAA GLOBEC program. Because the hydrographic and seismic data overlap in time and space, there is an opportunity to test the validity of ocean density models derived from seismic data and map the spatial extent of the eddies a times in the past when no other data to do this exist, thus extending the historical record. Reprocessing and inversion will be needed to optimize imaging of the fine-scale velocity/density structure of the ocean; most of the existing data have been processed using parameters that have distorted, and often eliminated, signals originating in the ocean rather than beneath the seafloor. Changes in ocean current regimes have broad impacts on ecology and climate. The project will also provide training for a graduate student in digital signal processing techniques of broad applicability in geophysics. Finally, the results will be used in public presentations that the PIs give in local schools and other forums designed to transmit the importance and excitement of earth science and oceanography.