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危险。 来自这些俯冲带的偶发但不可预测的地震会产生海底滑坡，称为浊积岩，产生危险的海啸波，可以淹没沿海城市，造成史诗般的破坏和大规模的死亡。 2011年日本东北部地震、浊流和由此引发的海啸造成15 899人死亡，就是这种灾害的一个最近例子，对基础设施的破坏一直持续到今天。 1964年阿拉斯加9.2级地震和海啸是现代袭击美国的最大地震事件，造成超过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个月的离岸实验，部署了海底仪器，以评估这一风险。华盛顿大学在这个实验中增加了一套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流的风险。 在目前的项目中，这些新的数据将从所有社区实验传感器中整合出来，以便（1）确定可以触发浊流和海啸的最小震级地震，（2）建立数值模型，以消除非地震阿拉斯加冬季风暴和洋流产生的误报警报，以及（3）帮助评估阿拉斯加俯冲带边缘产生可能威胁美国和加拿大西海岸的大海啸的潜力。 该项目包括支持华盛顿大学的一名研究生，他的博士论文包括评估俯冲带地震危险的培训，一位数值模拟师，他将构建阿留申群岛区域海洋模型，以帮助评估风暴和当地洋流漩涡产生的误报，以及一位识别俯冲带边缘海洋滑坡的专家。阿拉斯加俯冲带边缘14个月离岸实验中的地震计仪器。此外，华盛顿大学在这些地震仪上增加了105个传感器和数据记录器，专门用于识别本地和远程地震活动以及冬季风暴和剧烈海洋涡流环流引起的非地震引发所产生的浊流。 这项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，以及区域海洋模拟系统海洋环流模型的生成。 主要目标是开发更好的技术，纠正海洋现象的海底压力时间序列，以便最佳地识别长期地震事件和沉积物重力流。 具体而言，这项研究将综合多个观测代用指标，包括海底温度、稳定参考地点的压力、网络平均温度和压力、大气压力和海面高度，并生成一个数值模型，以改进海洋学海底压力预测和校正。海底仪器压力数据还将用于调查沿等深线求差的有效性，而不是使用深水单站参考数据集的传统方法。还将分析综合的群落实验数据，以获得浊流的短期温度信号诊断和更微妙的湍流信号以及来自长期悬浮沉积物的增强压力。 如果在阿拉斯加边缘发现浊流，地震数据和模型将用于评估触发机制和斜坡稳定性，其基础是条带测深图以及从存档钻探和活塞岩心中获得的沉积物特性。该奖项反映了NSF的法定使命，并被认为值得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来获得支持。

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.