Long-period Seismic Events Research Articles

The 1989–1990 eruptions of Redoubt Volcano: an introduction

Redoubt Volcano, located on the west side of Cook Inlet in south-central Alaska, erupted explosively on over 20 separate occasions between December 14, 1989 and April 21, 1990. Fourteen lava domes were emplaced in the summit area, thirteen of which were subsequently destroyed. The eruption caused economic losses estimated at over $160,000,000 making this the second most costly eruption in U.S. history. This economic impact provided the impetus for a integrated comprehensive account of an erupting volcano using both modern and classical research and modern techniques which in turn led to advances in eruption monitoring and interpretation. Research on such topics as dome formation and collapse and the resulting pyroclastic flows, elutriated ash, lightning, tephra, and flooding was blended with the rapid communication of associated hazards to a large user group. The seismology successes in predicting and monitoring eruption dynamics were due in part to (1) the recognition of long-period seismic events as indicators of the readiness of the volcano to erupt, and (2) to the development of new tools that allowed the seismicity to be assessed instantaneously. Integrated studies of the petrology of erupted products and volatile content over time gave clues as to the progress of the eruption towards completion.

Correlations between SO2 flux and long-period seismicity at Galeras volcano

THE 14 January 1993 eruption of Galeras volcano, in Colombia, which killed six scientists and three tourists1, was followed by a larger eruption on 23 March 19932. Both eruptions were preceded by episodes of long-period seismicity. The source of long-period seismic events has been modelled extensively3–8, as the resonance within a fluid-filled crack induced by pressure transients in the fluid5–7. Here we use the SO2 flux from Galeras volcano, measured remotely, to infer the degassing history during the episode of long-period events preceding the 23 March eruption. SO2 flux and long-period seismicity have been monitored separately elsewhere to forecast volcanic activity9–13. Our results show how the combination and correlation of the two methods can be used to interpret the movement of gases from the magma body to the surface, and to monitor the pressure buildup leading to an eruption at explosive volcanoes.

How we processed Apollo lunar seismic data

The Apollo lunar seismic station network gathered data continuously at a rate of 3 × 10 8 bits per day for nearly eight years until the termination in September, 1977. The data were processed and analyzed using a PDP-15 mini-computer. On average, 1500 long-period seismic events were detected yearly. Automatic event detection and identification schemes proved unsuccessful because of occasional high noise levels and, above all, the risk of overlooking unusual natural events. The processing procedures which were finally chosen consist of plotting all the data on a compressed time scale, visually picking events from the plots, transferring event data to separate sets of tapes and performing detailed analyses using the latter. Many problems remain, especially in the automatic processing of extra-terrestrial seismic signals.