The 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.
