BROAD-BAND RECORDING OF STROMBOLIAN EXPLOSIONS AND ASSOCIATED VERY-LONG-PERIOD SEISMIC SIGNALS ON MOUNT-EREBUS VOLCANO, ROSS ISLAND, ANTARCTICA

In December 1996 and January 1997, broadband seismometers were deploye d on the summit plateau of Mount Erebus at radial distances of 0.7, 1. 4 and 1.9 km from the central crater and lava lake. Strombolian explos ions at Erebus previously have been observed to produce seismic and ac oustic energy between 1 and 6 Hz. New observations document significan t energy viith spectral peaks as grave as 20 s. Nearly identical very- long-period (VLP) signals begin similar to 1.5 s prior to explosions, have dilatational onsets and persist for up to 150 s. Similar VLP wave forms were recorded at all three stations, indicating that the seismog rams are essentially source-dominated. Particle motions suggest an ini tial depth for the VLP source of up to several hundred meters, migrati ng deeper in the course of similar to 15 s. Such explosion-associated VLP signals may indicate a nondestructive lossy resonance or nonlinear fluid-flow excitation within the shallow magmatic system.