Abstract

Digital recording of Erebus seismic activity began on 25.11.88, using a PC-computer-based system in parallel with the Japanese analog tape recorder. Activity was very low. Daily earthquake counts ranged from zero to c20, and few of these were explosion earthquakes. Equipment on the volcano was mostly OK, but no picture was present on the TV transmission.

The heated plastic-coated window fitted to the camera housing last season was obscured by volcanic sublimates, and the camera had a serious intermittent fault which necessitated its return to Philips NZ Ltd, but Dr Phil Kyle of S-081 loaned his NTSC colour camera, which was installed on 9 December, and recorded at Scott Base until 30 December. The lava lake was so inactive that no incandescence was recorded, and only a few explosions were seen to eject bombs. After our repaired camera was reinstalled on 30 December, its superior infrared sensitivity revealed convecting hot lava not seen in the colour transmissions.

By 8 February, when the last recordings were dispatched from Scott Base, 177 digital earthquake recordings on floppy disk, and 16 explosions with ejected bombs had been recorded. Those processed so far, confirm that the foci obtained using stacked seismograms of explosion earthquakes, and a velocity of 4 km/s in the volcano, are much shallower and nearer to the lava lake, and have smaller RMS errors (0.02 s) than those obtained from individual explosion earthquakes using the old 2.1 km/s velocity (0.33+/−0.14 s).

Recording of the Windless Bight Infrasonic Array recommenced on 27.11.88 after a gap since late August 1988, due to tapes going astray in the Scott Base Store. Both field and lab equipment were still operating well, but the RTG Hut at Windless Bight was visited for safety checks, and to raise the antenna, and adjust the power supply. The off-line analysis computer was shifted to Victoria University, and the accumulated tapes since 1987 are being searched for signals from Erebus, and other volcanic eruptions world wide.