Detection of long-duration tremors at Deception Island volcano, Antarctica

Abstract

We analyze seismic data from permanent seismic stations located on Deception Island volcano, Livingston Island, and Cierva Cove, Antarctica, and identify a type of signal named Deception long-duration signals (DLDS). They are characterized by low amplitudes, long durations (several hours to days), frequency content limited to the 0.5–5Hz band, and are detected only at Deception Island. We develop a semi-automated method to systematically detect the occurrence of DLDS during February 2008–January 2015. We identify 276 DLDS episodes with amplitudes in the range of 0.5–2μm/s and durations from 3h to 13days. The temporal distribution shows an annual modulation, suggesting a seasonal effect. DLDS activity generally increases during the austral winter, although the annual distributions display two different behaviors. Some of them have a single maximum in the winter, while others are bimodal and show a second maximum during spring. Several mechanisms can explain the occurrence of long-duration signals. However, the only mechanism that explains the spectral content, duration, temporal distribution, and station coverage of the DLDS is the occurrence of volcanic tremors. Tremor generation at Deception Island has been explained by the resonance of fluid-filled conduits within the hydrothermal and/or shallow volcanic conduits. However, the long durations of the DLDS require a triggering mechanism that could be active for a long time span. The seasonal modulation of the DLDS suggests the influence of external effects. Most DLDS episodes can be related to periods with high-amplitude oceanic microseisms, which can induce an external forcing and introduce pressure variations in the volcanic/hydrothermal fluids. However, in some cases DLDS occur independently from oceanic noise amplitude. These cases precede summer surveys with large numbers of seismic events, indicating an increasingly restless state of the volcano. They can be produced by triggering mechanisms of internal, volcanic origin, such as the occurrence of changes in the stress distribution in the volcano edifice induced by magma dynamics, or fluctuations in the rate of volcanic gas supply.