We have mapped microearthquakes caused by magma migration preceding and during the flank and summit eruptions in March-May 2010 of Eyjafjallajökull stratovolcano in Iceland using a Coalescence Microseismic Mapping technique. Spatial and temporal clustering of >5,000 microearthquakes under the eastern flank of the volcano illuminates several northeast-southwest striking sub-vertical dikes at 2-6 km b.s.l., emplaced before the Fimmvörðuháls flank eruption in March. This intense precursory seismicity had a lateral extent of 6 km east-west and 3 km north-south. A sequence of 386 microearthquakes during the summit eruption, refined by double-difference relative relocation, defines a sub-linear trend inclined 5-10 deg from vertical extending from the upper mantle at 30 km depth to the summit crater. This sequence includes two major clusters at 19 km and 24 km b.s.l., each containing >100 earthquakes. All microearthquakes display characteristics of brittle fracture, with several subsets of events exhibi