VOLCANIC AND SEISMIC SWARM EVENTS ON THE REYKJANES RIDGE AND THEIR SIMILARITIES TO EVENTS ON ICELAND - RESULTS OF A RAPID RESPONSE MISSION

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 a bout 500 km southwest of Iceland was detected on both the Worldwide St andard Seismic Network (WWSSN) and Icelandic seismic networks. As part of a multi-institutional response to this swarm, the Naval Research L aboratory arranged for a P3 Orion Aircraft to deploy sonobuoys and AXB Ts in the immediate vicinity of the swarm activity. The detection of t he swarm motivated a survey of the region in 1990, using the towed Sea MARC II side-looking sonar system. In 1990-1991 the Russian Shirshov I nstitute of Oceanology offered the use of its MIR deep-diving submersi bles to investigate the rise axis for recent volcanism. During 1992, a scientific team comprised of five US and ten Russian scientists mobil ized 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 e ast of the large axial high in the center of our survey area. The leng th, width and depth range of the earthquakes were very similar to majo r seismic swarm events confined to fissure systems in the Krafla regio n of Iceland. It is likely that the earthquake swarm was located on a fresh, well-defined system of fissures and faults extending south of t he northernmost axial high studied. The earthquake swarm was probably associated with an emanation of lava creating a region of high backsca tter, located just to the east of the central axial high. In addition, the region of high-backscatter remains unsampled because it lay under neath the nadir of the processed SeaMARC tracks used to plan the subme rsible survey. However many samples were taken and structural studies of the evolving Reykjanes Ridge were carried out.