Array tracking of the volcanic tremor source at Deception Island, Antarctica

Abstract

Abstract. We have found experimental evidence which shows that the volcanic tremor recorded at Deception Island (South Shetland Islands, Antarctica) is a superposition in time of overlapping hybrid events. We studied data from a small aperture seismic array. Data analysis for tremor and hybrids included: (1) spectral analysis; (2) apparent slowness and back-azimuth determination by using the zero-lag cross-correlation method; and (3) polarization analysis. Both types of events share these common features: (a) two dominant spectral bands at frequencies 1-3 Hz (the most energetic) and 4-8 Hz; (b) several coherent phases with the same back-azimuth to the source and apparent slowness along the whole signal; (c) in the high frequency band, the apparent slowness is very low (around 0.17 s/km), indicating the propagation of body waves; (d) in the low frequency band, the apparent slowness is high (around 1.6 s/km), consistent with the presence of surface waves; and (e) clear P-wave onset followed by a complex pattern of Rayleigh waves. Therefore, both types of events are strongly related because they share the same source region, the same wave-propagation properties, and the same wave composition. Moreover, several arrivals, that resemble a single hybrid event, have been found along the tremor signals. Due to these reasons, we hypothesize that volcanic tremor of Deception Island is a superposition of hybrid type events. The source of both types could be the interaction between thaw water and hot materials in a shallow aquifer.

Nature, wavefield properties and source mechanism of volcanic tremor: a review

“…Injection of water into hot dry rock has been found to produce seismic signals similar to low-frequency volcanic earthquakes and supports the idea of a source that involves the opening of tensile cracks caused by excess £uid pressure (Bame and Fehler, 1986). The overall similarity of tremor and low-frequency events in the time and frequency domains, notwithstanding their di¡erent signal duration, has been pointed out by many authors as indicating that a common source may be at work, and which of the two seismic signals will be generated depends on the duration of the excitation mechanism (Fehler, 1983;Chouet, 1985;Hofstetter and Malone, 1986;Tsuruga et al, 1997;Almendros et al, 1997).…”

“…EtnaEreditato and Luongo, 1994;Wegler and Seidl, 1997) and is strongly in£uenced by path e¡ects. There are also a few studies that indicate a mixed composition of the wave¢eld with the presence of both body and surface waves (Deception Island, Almendros et al, 1997). Other studies utilised data from local arrays, by using the polarisation properties of the wave¢eld in order to calculate the backazimuth of the propagating waves and estimate the location of the source (Kilauea-Ferrazzini et al, 1991;Masaya-Me ¤taxian et al, 1997).…”

Evidence for enhanced bioavailability of trace elements in the marine ecosystem of Deception Island, a volcano in Antarctica

“…Deception Island is an active volcanic complex in the Antarctic Peninsula (Almendros, Ibanez, Alguacil, DelPezzo, & Ortiz, 1997;Rey, Somoza, & Martinez Frias, 1995). Geochemical analysis of caldera seafloor sediment shows a dominance of andesitic lava, rich in aluminum silicate (Baker, Davies, & Roobol, 1969;Rey et al, 1995).…”

The 1969 subglacial eruption on Deception Island (Antarctica): events and processes during an eruption beneath a thin glacier and implications for volcanic hazards

“…Geophysical investigations since 1987 have indicated that seismic activity on Deception Island is characterized by volcano-tectonic earthquakes, long-period and hybrid events, and tremor (Vila et al 1992;Almendros et al 1997). The 1969 seismogram and contemporary observations suggest that tremor and volcano-tectonic earthquakes were both involved in the activity (below), although the harmonic signature of very small volcano-tectonic earthquakes is not always separable in the comparatively crude record.…”

“…It is likely that both seawater and freshwater infiltrate the volcanic edifice and continuously replenish aquifers on the island (Vila et al 1992). For example, the incidence of tremor is roughly correlated with days on which there was rapid snow melt (Almendros et al 1997;Villegas et al 1997). Corrieg et al (1997) related tremor to vaporization of groundwater at depths of 2-3 km.…”