Volcanic tremor wave field during quiescent and eruptive activity at Mt. Etna (Sicily)

Ereditato, Davide; Luongo, G.

doi:10.1016/0377-0273(94)90006-x

Cited by 22 publications

(14 citation statements)

References 12 publications

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“…Etna for a time period spanning 6 years (1987^1993) during which di¡erent kinds of volcanic activity were at work, including periods of quiescence, Strombolian activity or lava fountaining (Ferrucci et al, 1990;Ereditato and Luongo, 1994;Wegler and Seidl, 1997). The polarisation analysis for the whole of this period revealed a persistent pattern of high values for the rectilinearity coe⁄cient with an east^west polarisation, suggesting that the wave¢eld consists of waves radiated by a vertical extended source aligned along the north^south direction.…”

Section: The Nature Of Volcanic Tremormentioning

confidence: 99%

“…The polarisation analysis for the whole of this period revealed a persistent pattern of high values for the rectilinearity coe⁄cient with an east^west polarisation, suggesting that the wave¢eld consists of waves radiated by a vertical extended source aligned along the north^south direction. The dominant wave types have been identi¢ed either as P waves (Ferrucci et al, 1990) or as Love/SH waves (Ereditato and Luongo, 1994;Wegler and Seidl, 1997) showing a complicated overlapping pattern. Similar observations have been reported for the tremor wave¢eld in other volcanoes, such as Arenal where the dominant wave type was identi¢ed as S waves by Benoit and McNutt (1997), whereas Hagerty et al (2000) reported a very complicated composition of the wave¢eld and were unable to identify any particular wave type.…”

Section: The Nature Of Volcanic Tremormentioning

confidence: 99%

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

Konstantinou

Schlindwein

2003

Journal of Volcanology and Geothermal Research

182

129

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Volcanic tremor has attracted considerable attention by seismologists because of its potential value as a tool for forecasting eruptions and better understanding the physical processes that occur inside active volcanoes. However, unlike tectonic earthquakes where the dominant source process is brittle failure of rock, the driving mechanism of tremor seems to involve complex interactions of magmatic fluids with the surrounding bedrock. These interactions are responsible for the following distinct characteristics found in volcanic tremor recorded at many volcanoes worldwide: (a) the onset of tremor may be emergent or impulsive, with its amplitude showing in many cases a direct relationship to the volcanic activity; (b) in the frequency domain the spectra consist of a series of sharp peaks in the band 0.1^7 Hz, representing either a fundamental frequency and its harmonics, or a random distribution, while quite often they exhibit temporal variations in their content; (c) the depth of the source can vary considerably from one volcano to another in the range of a few hundred metres to 40 km; (d) tremor may occur prior to and/or after eruptions with a duration that ranges from several minutes to several days or months. The methods used to study tremor include spectral analysis using both the Fast Fourier Transform and the Maximum Entropy Method, polarisation analysis of the wavefield and methods that make use of array data to deduce the backazimuth and type of the seismic waves as well as the location of the source. Visual and/or recorded acoustic observations of the ongoing volcanic activity have assisted in many cases to further constrain proposed physical mechanisms for the generation of tremor. The models suggested as possible sources of tremor can be grouped as follows: (a) fluid-flow-induced oscillations of conduits transporting magmatic fluids; (b) excitation and resonance of fluid-filled cracks; (c) bubble growth or collapse due to hydrothermal boiling of groundwater; (d) a variety of models involving the oscillations of magma bodies with different geometries. It has been proposed by many authors that the source of tremor is not unique and may differ from one volcano to another, a fact that adds more difficulty in the source modelling efforts. As data quality, computer power and speed are improving, it may be possible in the near future to decipher and accurately model tremor source processes at different volcanic environments. ß 2002 Elsevier Science B.V. All rights reserved.

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Section: The Nature Of Volcanic Tremormentioning

confidence: 99%

Section: The Nature Of Volcanic Tremormentioning

confidence: 99%

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

Konstantinou

Schlindwein

2003

Journal of Volcanology and Geothermal Research

182

129

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“…This could indicate that Love waves become more important with increasing distance. For comparison, Ereditato and Luongo (1994) have made a study on volcanic tremor at Etna, and they likewise found a large amount of Love waves.…”

Section: Particle Motion At the Onset Of The Eruptionmentioning

confidence: 99%

Volcanic tremor related to the 1991 eruption of the Hekla volcano, Iceland

Soosalu

Einarsson

Jakobsdóttir

2003

Bulletin of Volcanology

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Volcanic tremor at the Hekla volcano is directly related to eruptive activity. It starts simultaneously with the eruptions and dies down at the end of them. No tremor at Hekla has been observed during noneruptive times. The 1991 Hekla eruption began on 17 January, after a short warning time. Local seismograph stations recorded small premonitory earthquakes from 16:30 GMT on. At 17:02 GMT, low-frequency volcanic tremor became visible on the seismograph records, marking the onset of the eruption. The initial plinian phase of the eruption was short-lived. During the first day several fissures were active but, by the second day, the activity was already limited to a segment of one principal fissure. The eruption lasted almost 53 days. At the end of it, during the early hours of 11 March, volcanic tremor disappeared under the detection threshold and was followed by a swarm of small earthquakes. At the start of the eruption, the tremor amplitude rose rapidly and reached a maximum in only 10 min. The tremor was most vigorous during the first hour and started to decline sharply during the next hour, and later on more gently. During the eruption as a whole, the tremor had a continuous declining trend, with occasional increases lasting up to about 2 days. Spectral analysis of the tremor during the first 7 h of the eruption shows that it settled quickly, within a couple of minutes, to its characteristic frequency band, 0.5-1.5 Hz. The spectrum had typically one dominant peak at 0.7-0.9 Hz, and a few subdominant peaks. Hekla tremor likely has a shallow source. Particle motion plots suggest that it contains a significant component of surface waves. The tremor started first when the connection of the magma conduit with the atmosphere was reached, suggesting that degassing may contribute to its generation.

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“…Assuming that Dc and t are known respectively within €3 m and €30 s, the uncertainty on the source depth is €180 m. Eventually, because of all simplifying assumptions made, we consider a source depth located at a few hundred meters, in agreement with studies of other authors at Etna (e.g. Schick and Riuscetti 1973;Ereditato and Luongo 1994) and Stromboli (Chouet et al 1999;Vergniolle 2001). Note that with the more hypothetical 35-min delay between radar and tremor signals, the reservoir would be located at a depth of about 7 km, consistent with seismic studies (Laigle and Hirn 1999;Laigle et al 2000).…”

Section: Discussionmentioning

confidence: 87%

Doppler radar sounding of volcanic eruption dynamics at Mount Etna

et al. 2003

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Besides their common use in atmospheric studies, Doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field. We present the observations made with a mid-power UHF Doppler radar (Voldorad) during a 7-h Strombolian eruption at the SE crater of Mount Etna on 11-12 October 1998. Main characteristics of radar echoes are retrieved from analysis of Doppler spectra recorded in the two range gates on either side of the jet axis. From the geometry of the sounding, the contribution of uprising and falling ejecta to each Doppler spectrum can be discriminated. The temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before, during and after its paroxysm. Moreover, during the sharp decrease of eruptive activity following the paroxysm, detailed analysis of video (from camera recording), radar and seismic measurements reveals that radar and video signals start to decrease simultaneously, approximately 2.5 min after the tremor decline. This delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the SE crater. Detailed analysis of eruptive processes has been also made with Voldorad operating in a high sampling rate mode. Signature of individual outburst is clearly identified on the half part of Doppler spectra corresponding to rising ejecta: temporal variations of the backscattered power exhibit quasi periodic undulations, whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time. Periodicity of power variations (between 3.8 and 5.5 s) is in agreement with the occurrence of explosions visually observed at the SE vent. Maximum vertical velocities of over 160 m s 1 were measured during the paraoxysmal stage and the renewed activity. Finally, by using a simplified model simulating the radar echoes characteristics, we show that when Voldorad is operating in high sampling rate mode, the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam.

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Volcanic tremor wave field during quiescent and eruptive activity at Mt. Etna (Sicily)

Cited by 22 publications

References 12 publications

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

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

Volcanic tremor related to the 1991 eruption of the Hekla volcano, Iceland

Doppler radar sounding of volcanic eruption dynamics at Mount Etna

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