Arctic Basin Earthquake Detection with the Spinnaker Hydrophone Array

主要研究人员将使用美国海军在北极冰盖下记录的水听器阵列数据来研究加克尔岭的地震活动性。水声技术可通过分析海底界面处地震能量转换为声能所产生的T波来探测和定位地震事件。 由于T波的传播效率比体波高得多，因此水声方法可以检测到大量陆基台站无法检测到的小震级地震。 在东北太平洋，水声技术得到了非常成功的应用，利用水听器数据，包括首次从海底扩张事件中获得的实时地震数据，探测到了太平洋西北部地方陆地地震台站无法探测到的数千个洋中脊构造和火山事件，并确定了这些事件的位置。联合S.海军“三角帆”阵列是一个独特的，128元水听器阵列部署在84 'N，62' W。 三个月的三角帆阵列数据已经获得。 主要研究人员将在一项试点研究中展示北极盆地区域和地震研究的可行性，方法是使用T波走时和波束形成技术定位斯匹次卑尔根断裂带的区域事件，并检测距离高达11，000公里的大地震的地震阶段。这些研究表明，Spinnaker台阵的信噪比和频率响应特性非常适合探测北极盆地内的地震能量。这项研究应通过使用方位形成和台阵处理技术，将台阵“指向”加克尔海岭，并搜寻全球地震台网（GSN）或北极陆地阵列。 基于之前的水声实验，他们期望将地震检测阈值从体波震级Mb ~！4.5到Mb ~！2.0，这将导致观察到的事件比目前看到的GSN多几百倍。降低北极盆地地震活动的检测阈值对于解开该地区的构造是重要的。 加克尔海岭是一个神秘的特征，明显缺乏转换偏移，巨大的自由水重力异常，以及世界上扩张最慢的板块边界。 由于在Gakkel海岭部署当地地震阵列在后勤上困难重重，而且费用昂贵，因此水声技术可能是研究这一区域最具成本效益的手段。 这项研究应能更好地了解加克尔海岭的地震活动，所开发的技术可直接用于北极盆地和加克尔海岭的综合地震监测系统。

AbstractOPP 98-13140The Principal Investigators will use hydrophone array data recorded by the U.S. Navy under the Arctic ice cap to study the seismicity of the Gakkel Ridge. Hydroacoustic techniques allow for the detection and localization of seismic events through the analysis of T waves generated by the conversion of seismic to acoustic energy at the seafloor interface. Because T waves propagate much more efficiently than body waves, hydroacoustic methods can allow for the detection of large numbers of small-magnitude earthquakes that are not detected by land based stations. Hydroacoustic techniques have been applied very successfully in the northeast Pacific, where thousands of mid-ocean ridge tectonic and volcanic episodes, too small to be detected by local land seismic stations in the Pacific northwest, have been detected and localized with hydrophone data, including the first ever real-time seismic data from seafloor spreading events. The U. S. Navy "Spinnaker" array is a unique, 128 element hydrophone array deployed at 84'N, 62'W. Three months of Spinnaker array data have been acquired. The Principal Investigators will demonstrate the feasibility of regional and teleseismic earthquake studies in the Arctic Basin in a pilot study by using T wave travel time and beamforming techniques to localize a regional event from the Spitsbergen Fracture Zone, and to detect teleseismic phases from large earthquakes at ranges up to 11,000 km. These studies have demonstrated that the signal-to-noise ratio and frequency response characteristics of the Spinnaker array are well-suited to the detection of seismic energy from within the Arctic Basin.This research should advance Arctic Basin tectonic studies by using bearnforming and array processing techniques to "point" the array towards the Gakkel Ridge and search for low-magnitude earthquakes that were not detected by the Global Seismic Network (GSN) or Arctic land arrays. Based on previous hydroacoustic experiments, they expect to lower the earthquake detection threshold from body wave magnitude Mb ~! 4.5 to Mb ~! 2.0, which should result in the observation of several hundred times more events than currently seen by the GSN.Decreasing the detection threshold of Arctic Basin seismicity is important for unraveling the tectonics of the region. The Gakkel Ridge is an enigmatic feature with an apparent lack of transform offsets, anomalously large free-water gravity anomalies, and the slowest spreading plate boundary in the world. Because the deployment of local seismic arrays on the Gakkel Ridge is logistically difficult and expensive, hydroacoustic techniques may provide the most cost-effective means to study this region. This study should provide a better understanding of Gakkel Ridge seismicity, and the techniques developed can be directly applied towards a comprehensive seismic monitoring system for the Arctic Basin and the Gakkel Ridge.