In 1999 lasting over 7 months, the largest ever earthquake swarm at a mid-ocean ridge was teleseismically registered worldwide. It featured 252 recorded events, including 11 events with a magnitude mb>5.0 and originated from around 85°E at the eastern Gakkel Ridge (full spreading rate 6-14 mm/yr). This makes it indicative for active spreading processes at ultraslow spreading ridges where heat loss by conductive cooling is thought to decrease magma supply and focus magmatism in widely spaced discrete volcanic centres. The relocalization was done with the routine NonLinLoc using a probabilistic approach. The new locations of the epicentres show a clustering of events within the central rift valley and the southern rift flank, the 68% error in ellipse semi-major axes of the new localization is in the order of 15 km for the best events. An analysis of the respective epicentral distance to the volcanic complex with advancing time showed high seismicity and diffuse activation around the volcanic complex within the rift valley before the 15th of April, to the NW migrating epicentres with additional activation of the valley walls and a marked drop in seismicity after April 15th. We postulate that the change in seismicity rate and the following change in source mechanism might mark the onset of volcanic activity and may be reflected by three events with highly correlating waveforms at the beginning of April.