Volcanic tremors at Deception Island (South Shetland Islands, Antarctica)

Abstract

Deception Island (62°43′S, 60°57′W) is an active volcano located at the spreading centre of the Bransfield Strait backarc on the southwestern side of the Scotia Sea region (Antarctica). Since 1986, the Spanish Antarctic National Program has supported geophysical and geological surveys addressed to the study of seismic and volcanic activities in the area. The present volcanotectonic activity is restricted to significant seismic activity and several fumarole fields. Numerous earthquakes, with magnitudes ranging from 0.1 to 2.2, have been recorded, most of them distributed along the main fractures of the island, which coincide with the regional structural trend of the Bransfield Strait back-arc. Several types of volcanic tremors have also been recorded, all of them with high spectral stability contents with few and well-defined spectral peaks. The location of the stations that record tremors, the correlation of seismic noise with the tremors and the geological characteristics of Deception Island, together suggest that the tremors are generally associated with geothermal noise originated in the uppermost ducts of the fumarolian system. If we associate the surficial ducts to harmonic oscillators, it is observed that the motion is basically unidirectional, as is expected in the degasification of an aquifer. Taking the main observed frequencies and applying the classical mechanical expressions of organ pipes, we obtain a duct length which agrees with the length of a water column necessary to maintain the equilibrium as indicated by the application of the Clausius-Clapeyron equation.