Arctic Basin Earthquake Detection with the Spinnaker Hydrophone Array

摘要：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Gakkel Ridge的地震活动性。水声技术可以通过分析海底界面处地震能转化为声能所产生的T波来探测和定位地震事件。由于T波比体波传播效率高得多，水声方法可以探测到陆地台站无法探测到的大量小震级地震。水声技术在太平洋东北部的应用非常成功，在那里，数千个洋中脊构造和火山事件太小，太平洋西北部的当地陆地地震台站无法探测到，但水听器数据已经被探测到并定位，包括有史以来第一次来自海底扩张事件的实时地震数据。美国海军“三角帆”阵列是一种独特的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。首席研究人员将在一项试点研究中展示北极盆地区域和远震地震研究的可行性，通过使用T波传播时间和波束形成技术来定位斯匹次卑尔根断裂带的区域事件，并检测距离达11,000公里的大地震的远震阶段。这些研究表明，Spinnaker阵列的信噪比和频率响应特性非常适合于北极盆地内地震能量的探测。这项研究应该通过使用信息形成和阵列处理技术将阵列“指向”Gakkel Ridge，并搜索全球地震台网（GSN）或北极陆地阵列未检测到的低震级地震，从而推进北极盆地构造研究。基于先前的水声实验，他们期望降低体波震级Mb ~！4.5到Mb ~！2.0，这将导致观测到的事件比GSN目前看到的要多几百倍。降低北极盆地地震活动性的探测阈值对于揭示该地区的构造具有重要意义。Gakkel Ridge是一个神秘的特征，明显缺乏变换偏移，异常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 Ridge上部署本地地震阵列在后勤上困难且昂贵，水声技术可能是研究该地区最具成本效益的手段。本研究为进一步了解Gakkel Ridge地震活动性提供了依据，并可直接应用于北极盆地和Gakkel Ridge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.