Discriminating slow slip earthquakes and sediment gravity flows from oceanographic signals: the Alaska Amphibious Community Seismic Experiment

俯冲带是美国沿海人口中心最严重的地震灾害。来自这些俯冲带的间歇性但不可预测的地震会产生被称为浊积岩的海底滑坡，产生危险的海啸波，可以淹没沿海城市，造成巨大的破坏和大规模的死亡。2011年的日本东北地震、浊积和由此引发的海啸就是这种危害的一个最新例子，造成15899人死亡，对基础设施的破坏一直持续到今天。1964年发生在阿拉斯加边缘的9.2级地震和海啸是美国现代史上最大的地震事件，造成了超过23亿美元的损失，并清楚地指出了俯冲带地震和海啸对美国沿海城市的潜在风险。最近进行的国家科学基金会社区地震实验在阿拉斯加边缘进行了为期14个月的海上实验，部署了海底仪器，以评估这种风险。华盛顿大学在这个实验中增加了一套额外的传感器和数据记录器，专门用于评估阿拉斯加边缘地震引发的浊积流的风险。在当前的项目中，这些新数据将整合来自所有社区实验传感器的数据，以便(1)确定可能引发浊流和海啸的最小震级地震，(2)生成数值模型，以消除由非地震阿拉斯加冬季风暴和洋流产生的误报警报。(3)帮助评估阿拉斯加俯冲带边缘产生潜在威胁美国和加拿大西海岸的大海啸的可能性。该项目包括对一名华盛顿大学研究生的支持，该研究生的博士论文包括评估俯冲带地震危害的培训，一名数值建模师将构建阿留申岛区域海洋模型，以帮助评估风暴和当地洋流涡流产生的误报，以及一名识别俯冲带边缘海洋滑坡的专家。最近，美国国家科学基金会阿拉斯加两栖社区地震实验在阿拉斯加俯冲带边缘进行了为期14个月的海上实验，部署了74台海底地震仪。此外，华盛顿大学为这些地震仪增加了额外的105个传感器和数据记录器，专门用于识别由本地和远程地震活动产生的浊度流，以及由冬季风暴和强烈的海洋涡流环流引起的非地震引发的浊度流。本研究将利用社区实验地震数据、海底压力和温度数据的可用性，并生成区域海洋模拟系统海洋环流模型。主要目标是开发改进的技术来校正海底压力时间序列的海洋现象，以便优化长时间地震事件和沉积物重力流的识别。具体而言，该研究将整合多个观测指标，包括海底温度、稳定参考站点的压力、网络平均温度和压力、大气压力和海面高度，并生成一个数值模式，以改进海洋底部压力的预测和校正。海底仪器压力数据也将用于研究沿等深线差分的有效性，而不是使用深水单站参考数据集的传统方法。综合的社区实验数据还将用于分析短期温度信号、浊度流诊断和更细微的前兆流信号以及来自长期悬浮沉积物的压力增强信号。如果在阿拉斯加边缘确定了浊度流动，地震数据和模型将用于评估触发机制和边坡稳定性，这些机制和稳定性是基于岸线测深图，以及从存档钻井和活塞岩心获得的沉积物特性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zones represent the most serious seismic hazard to United States coastal population centers. The episodic but unpredictable earthquakes from these subduction zones generate undersea landslides called turbidites that produce dangerous tsunami waves that can inundate coastal cities, producing epic damage and large-scale fatalities. The 2011 Tohoku earthquake, turbidite and resulting tsunami that claimed 15,899 deaths in Japan is a recent example of this hazard, where the damage to infrastructure continues to the present day. The 1964 Magnitude 9.2 Alaska margin earthquake and tsunami was the largest seismic event to hit the United States in modern times, causing over $2.3 billion dollars in damage and pointing clearly to the potential risks of subduction zone earthquakes and tsunamis to U.S. coastal cities. The recently-conducted National Scientific Foundation Community Seismic Experiment deployed ocean bottom instruments in a 14-month off-shore experiment on the Alaska margin in order to assess this risk. An additional suite of sensors and data loggers was added to this experiment by the University of Washington, specifically to evaluate the risk from turbidite currents initiated by Alaskan margin earthquakes. Within this current project, these new data will be integrated from all of the community experiment sensors in order to (1) determine the minimum magnitude earthquake that can trigger both turbidity currents and tsunamis, (2) produce numerical models to eliminate the production of false positive alarms that are generated from non-seismic Alaskan winter storms and ocean currents, and (3) help assess the potential for the Alaska Subduction Zone margin to produce the large tsunamis that potentially threaten the west coast of the United States and Canada. The project includes support for a UW graduate student whose PhD thesis includes training in evaluating subduction zone seismic hazards, a numerical modeler who will construct an Aleutian Island regional ocean model to help evaluate false positives produced by storms and local ocean current eddies and an expert in identifying marine landslides on subduction zone margins.The recent NSF Alaska Amphibious Community Seismic Experiment deployed 74 Ocean Bottom Seismometer instruments in the 14-month off-shore experiment on the Alaska subduction zone margin. In addition, the University of Washington added an additional 105 sensors and data loggers to these seismometers, specifically to identify turbidity currents generated by both local and distant seismic activity and by non-seismic initiation due to winter storms and vigorous ocean eddy circulation. This study will leverage the availability of the Community Experiment seismic data, bottom pressure and temperature data, and the generation of a regional ocean modeling system ocean circulation model. The primary goal is to develop improved techniques to correct bottom pressure time series for oceanographic phenomena in order to optimize the identification of long-duration seismic events and sediment gravity flows. Specifically, the study will integrate the multiple observational proxies which include bottom temperature, pressures at a stable reference site, network-averaged temperatures and pressures, atmospheric pressures and sea surface heights, together with the generation of a numerical model to improve oceanographic bottom pressure predictions and corrections. The seafloor instrument pressure data will also be used to investigate the effectiveness of differencing along-isobaths rather than the traditional approach of using a deep-water single-station reference dataset. The combined Community Experiment data will also be analyzed for short-term temperature signals diagnostic of turbidity currents and more subtle signals of precursory flows and enhanced pressures from long-lived suspended sediments. If turbidity flows are identified on the Alaskan margin, seismic data and models will be used to assess the triggering mechanisms and slope stability based on swath bathymetry maps, and sediment properties obtained from archive drilling and piston cores.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.