Local seismicity following the 1998 eruption of Axial Volcano

A local network of seven ocean bottom hydrophones was deployed on Axial vol cano 14 days after the onset of seismic activity from the January 1998 diki ng/eruption episode. Eighty-one locatable microearthquakes were observed du ring a 166 day deployment. The first group of events, observed immediately after the eruption, cluster around the rim of the central caldera. These ev ents are believed to be aftershocks from the major caldera collapse at the beginning of the diking event. The second group of events, observed 2-5 mon ths after the eruption, are primarily located on a line striking 125 degree s from the caldera onto the southeast shoulder of the volcano, with a few e vents extending into Helium basin to the north. These events are interprete d to result from horizontal shear associated with the CoAxial and Vance rid ge segment offset, or extension across the Juan de Fuca/Pacific plate bound ary underlying the eastern flank of Axial volcano.