Moment tensors of microearthquakes from the Eyjafjallajökull volcano in South Iceland

Analyses of relative P- and S-wave amplitudes of 15 selected earthquakes (M_L <2.3) from a seismic swarm, which occurred in May and June 1994 at the Eyjafjallajoökull volcano in South Iceland, reveal similar radiation patterns, a thrust-type double-couple with an additional source component. All focal solutions have nearly vertical T-axes and horizontally oriented P-axes, with E-W-oriented nodal planes. The volume increase corresponding to an isotropic source component is estimated to be in the range of 24 m³. The temporal and spatial seismic pattern, small magnitude range, focal mechanisms and depth range of the Eyjafjallajökull earthquakes indicate vertical intrusion of magma into a confined region at the northern flank of the volcano.