Arctic Basin Earthquake Detection with the Spinnaker Hydrophone Array

OPP 98-13140首席调查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海脊的地震活动。水声技术能够通过分析在海底界面将地震能量转换为声能而产生的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，因此水声方法可以探测到陆基台站无法探测到的大量小震级地震。水声技术在东北太平洋得到了非常成功的应用，在那里探测到了数以千计的大洋中脊构造和火山幕，这些构造和火山幕太小，太平洋西北部的当地陆地地震台无法探测到，并利用水听器数据，包括有史以来第一次来自海底扩展事件的实时地震数据进行了定位。美国海军“Spinnaker”阵列是一种独特的128元水听器阵列，部署在北纬84‘，西经62’处。已经获得了三个月的Spinnaker阵列数据。首席调查员将在一项试点研究中论证北极盆地区域和远震地震研究的可行性，方法是使用T波走时和波束形成技术来定位斯皮茨卑尔根断裂带的区域事件，并从范围达11 000公里的大地震中检测远震震相。这些研究表明，Spinnaker台阵的信噪比和频率响应特性非常适合于探测北极盆地内部的地震能量。这项研究应该通过使用方位形成和台阵处理技术来推进北极盆地构造研究，将台阵“指向”Gakkel海脊，并寻找全球地震台网(GSN)或北极陆地台阵没有检测到的低震级地震。根据之前的水声实验，他们预计将体波震级Mb4.5降至Mb2.0，这将导致观测到的地震比GSN目前看到的事件多几百倍。降低北极盆地地震活动的探测阈值对揭示该地区的构造具有重要意义。Gakkel海脊是一个神秘的特征，它明显缺乏转换偏移量，异常大的自由水重力异常，以及世界上最慢的扩张板块边界。由于在Gakkel Ridge部署当地地震阵列在后勤上困难且成本高昂，水声技术可能为研究该地区提供最具成本效益的手段。这项研究应能更好地了解Gakkel Ridge的地震活动，所开发的技术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.