On 21 May 1989, a major earthquake swarm on the Reykjanes Ridge at 59 degrees 43' N, 29 degrees 32' W at a water depth of about 1000 m and about 500 km southwest of Iceland was detected on both the Worldwide Standard Seismic Network (WWSSN) and Icelandic seismic networks. As part of a multi-institutional response to this swarm, the Naval Research Laboratory arranged for a P3 Orion Aircraft to deploy sonobuoys and AXBTs in the immediate vicinity of the swarm activity. The detection of the swarm motivated a survey of the region in 1990, using the towed SeaMARC II side-looking sonar system. In 1990-1991 the Russian Shirshov Institute of Oceanology offered the use of its MIR deep-diving submersibles to investigate the rise axis for recent volcanism. During 1992, a scientific team comprised of five US and ten Russian scientists mobilized the twin, deep diving Russian submersibles to study the spreading axis of the Reykjanes Ridge. The resulting data analyses allows us to conclude that the 1989 seismic swarm event occurred adjacent to and east of the large axial high in the center of our survey area. The length, width and depth range of the earthquakes were very similar to major seismic swarm events confined to fissure systems in the Krafla region of Iceland. It is likely that the earthquake swarm was located on a fresh, well-defined system of fissures and faults extending south of the northernmost axial high studied. The earthquake swarm was probably associated with an emanation of lava creating a region of high backscatter, located just to the east of the central axial high. In addition, the region of high-backscatter remains unsampled because it lay underneath the nadir of the processed SeaMARC tracks used to plan the submersible survey. However many samples were taken and structural studies of the evolving Reykjanes Ridge were carried out.
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