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Victoria University Antarctic Research Expedition Science and Logistics Reports 1974-75: VUWAE 19

Erebus expedition (Seismic studies)

Erebus expedition (Seismic studies)

  1. Three slow motion type seismographs (Dibble, 1964) and an ink chart recorder of seismic power (Dibble, 1969) were used to record at 5 sites: 3 surrounding the main crater at a radius of 1 km; one in the ice cave near the camp at 0.5 km radius; and one near the main crater centre. Twentysix [sic] days of recording were obtained between December 3 and 31, including 12 days with simultaneous recording at all 5 sites.
  2. No volcanic tremor was recorded, but an average of 1000 volcanic page 10 earthquakes per day in a range of 0.1 to 106J were recorded. The parameter "b" (Richter, 1958) for a sample of 1000 earthquakes had the value of 1.2.
  3. In a total of 24 hours of documented visual observations of the inner crater, all earthquakes of 103J or more were explosion earthquakes corresponding with explosions of either the main vent or the lava lake. Some smaller earthquakes were accompanied by eruptions, but those accompanying the bursting of large bubbles in the lava lake were too small to be recorded. However most earthquakes were B-type volcanic earthquakes (Minakami, 1963) not accompanied by audio-visual activity, but otherwise similar to explosion earthquakes.
  4. It was not possible to predict safe periods for the descent into the inner crater from the seismic recordings, and as yet, the type and location of the explosions and eruptions cannot be recognised from the seismograms because they are all different. However the general level of activity over long periods could undoubtedly be followed by means of a radio telemetry seismograph at the southernmost of the 5 sites, recording at Scott Base. This would aid the planning of future expeditions to the volcano.