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  • 1
    Electronic Resource
    Electronic Resource
    Seismological Evidence of Active Faulting in the Tendaho Rift (Afar Triangle, Ethiopia) (1997)
    Springer
    Pure and applied geophysics 149 (1997), S. 357-374 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Afar Triangle, Tendaho Rift, microearthquakes, S-wave splitting.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —A temporary network has been used to study the seismic activity in the central-northern part of the Tendaho Rift (Afar Triangle, Ethiopia). Small size earthquakes (M 〈 2.5) characterize the seismicity during the time interval 1993–1994 when the seismic array was operating. Shocks are mainly located in the central part of the Tendaho rift and their epicentral distribution highlights a remarkable coincidence with NW-SE trending tectonically active structures. Focal depths are confined in the range of 3–8 km.   The few acceptable fault plane solutions suggest the occurrence of both strike-slip and dip-slip rupture mechanisms, which are often characterized by a nodal plane oriented approximately NW-SE.  A detailed study of earthquake waveforms using polarization analysis showed the occurrence of splitting phenomena for the S waves. Despite the differences in focal mechanisms, the similarity of the faster S-wave directions (NW-SE to NNW-SSE) suggests that the direction of geological structures and/or the systems of fractures adjacent to the faults could bias shear-wave propagation. The splitting time between fast and slow shear waves shows no systematic relationship with either hypocentral distance or focal depth, suggesting that the anisotropic volume is constrained to depths shallower than 3 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050030
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  • 2
    Electronic Resource
    Electronic Resource
    Review of seismological studies at Mount Etna (1987)
    Springer
    Pure and applied geophysics 125 (1987), S. 951-970 
    Details
    ISSN: 1420-9136
    Keywords: Mt. Etna ; earthquakes ; eruptions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper reports the present state of seismological research at Mt. Etna. A schematic classification of the earthquakes that occur on the volcano is proposed, based on both seismogram and spectrum features. We have made both focal solutions and estimates of earthquake source parameters (stress drop values between 2 and 20 bars and small source dimensions). The crust of Etna thus appears as an extremely heterogeneous medium that does not permit great stress accumulation. The coexistence of an extensional regime with an older and deeper compressive one seems confirmed at depths greater than about 7 km. Eruptive and seismic phenomena occur mainly along the principal structural trends of the volcano, but often the directions of the eruptive fractures and the earthquake concentration during the same eruption do not coincide. Tectonics seem to play an important role in controlling seismo-volcanic behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879362
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  • 3
    Electronic Resource
    Electronic Resource
    Volcanic tremor at Mt. Etna: State-of-the-art and perspectives (1987)
    Springer
    Pure and applied geophysics 125 (1987), S. 1079-1095 
    Details
    ISSN: 1420-9136
    Keywords: Mt. Etna ; volcanic tremor ; eruptive precursors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Volcanic tremor on Etna seems to have its origin within the main magma feeding system. On the basis of both spectral analyses at two permanent seismic stations and periodical measurements along the slopes of the volcano, two distinct sources are proposed. The former, characterized by low frequency contents (f〈1.5 Hz), is located in a 2 km deep flat magma chamber, whereas the latter source seems to be linked to the upper part of the active vents. Turbulent motions in the magma-gas mixture, induced by escaping gases within the conduits, is one proposed cause of volcanic tremor on Etna (Seidl et al., 1981). From spectral analyses we propose approximate models of the feeding system of the main summit craters. Time variations of tremor energy were also investigated, and no regular patterns have been observed for the studied eruptions. More systematic information seems to be needed for a better knowledge of both the source model and location, and correlation between tremor features and volcanic activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879369
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  • 4
    Electronic Resource
    Electronic Resource
    Attenuation of short period seismic waves at Etna as compared to other volcanic areas (1987)
    Springer
    Pure and applied geophysics 125 (1987), S. 1039-1050 
    Details
    ISSN: 1420-9136
    Keywords: Q ; volcanic earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract CodaQ for Etna volcano is frequency dependent and theQ frequency pattern and the numerical values ranging from about 100 at 1 Hz to about 300 at 18 Hz are similar to the values obtained for other volcanoes: Campi Flegrei, Aeolian Islands and Hawaii. Moreover the frequency pattern and the numerical values of coda quality factor, for most of the seismically active zones of Italy are very different from those of the volcanic zones. Several studies of the location of magma chambers show the presence of magma pockets beneath Lipari and Vulcano Islands of the Aeolian archipelago and an anomalous low velocity body beneath Etna. These evidences suggest that a possible interpretation of the characteristic frequency pattern ofQ on volcanic areas is that the presence of magma can modify the scattering environment and consequently the codaQ estimates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879367
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  • 5
    Electronic Resource
    Electronic Resource
    Volcanic tremor at Mount Etna (January 1984–March 1985): its relationship to the eruptive activity and modelling of the summit feeding system (1991)
    Springer
    Bulletin of volcanology 53 (1991), S. 309-320 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Spectral analyses of volcanic tremor at Etna during January 1984–March 1985, have been performed and the relationship between tremor energy and observed volcanic phenomena have been examined. The highest energy levels have been observed during the paroxysmal phases of eruptions, whereas a gradual decrease was linked to the lowering of eruptive activity. Amplitude variations with time of some spectral frequency peaks (0.95, 1.20, 1.45, 1.65, 1.80 and 2.40 Hz) have been compared with volcanic activity at the summit craters, and on the basis of these results a new schematic diagram for the feeding system of the summit vents is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414527
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  • 6
    Electronic Resource
    Electronic Resource
    Earthquake activity during the 1983 Etna eruption (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 953-963 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Seismic stations, with automatic P-picking and satellite retransmission were set up on Mount Etna following the eruption started on March 1983. Positions of the stations were chosen in order to complement the permanent telemetered network of Catania University. Comparison between locations obtained by both networks were made for earthquakes recorded by at least 5 ARGOS DCP (Data Collection Platform) stations. We observed a satisfactory agreement for events inside both networks. By merging data of both networks, it has been possible to locate more than 50 earthquakes for which separate computation was not possible due to the low number of arrivals. On 3rd-4th June a swarm of deep seismic events was observed. Hypocenters of these earthquakes are clearly located in a NNW-SSE-trending vertical zone of 5 km width at a depth of 7–36 km. Changes in the distribution of shallow seismic activity, before and after this swarm, have been observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952354
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  • 7
    Electronic Resource
    Electronic Resource
    Time variation of b and Q"c at Mt. Etna (1981-1987)
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 71 (1992), S. 137-140 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(92)90070-C
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  • 8
    Electronic Resource
    Electronic Resource
    Seismic activity preceding the 1983 eruption of Mt. Etna (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 941-952 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The March–August, 1983 eruption of Mt. Etna can be considered as one of the most important in the last years. The analysis of seismic activity during the three months immediately before the eruption showed interesting variations of theb coefficient, in the frequency-magnitude relationship, that have been linked to possible changes of the stress field in the Etnean region. The eruption start was also preceded by a strong seismic crisis with epicenters mostly on the southern, eastern and southwestern flanks of the volcano, and characterized by the shallowness of most of the events (h≤3 km). The data analysis has led to a hypothesis on the eruption occurrence based on a model of dynamic evolution of the stress field acting on Mt. Etna.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952353
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  • 9
    Electronic Resource
    Electronic Resource
    An approach to problems on energy sources at Mount Etna based on seismological and volcanological data (1987)
    Springer
    Bulletin of volcanology 49 (1987), S. 729-736 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Based on seismograms from the most continuously operating station of the seismic network at Mt. Etna (Monte Vetore, 1665 m a.s.l.), the energy release patterns through time have been obtained for volcanic tremors and earthquakes which occurred between 1978–1982. Both energies range between 1011∓1013 J/a, but their release patterns are not strictly correlated to each other. Considering only the eruptions which occurred during the same time span, the amount of thermal energy released and the associated potential energy needed to raise the magma to the surface from a 2-km-deep hydrostatic equilibrium level were estimated to be about 1017 and 1015 J/a, respectively. The computed energies for earthquakes and tremors are at least one order of magnitude less than what is needed to match a model of magma transport based solely on the jerky propagation of melt-filled cracks. The energy needed to raise the magma to the surface could be supplied by expanding gases in the upper levels of the magma column and/or by tectonic stresses acting on shallow batches of magma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01079824
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  • 10
    Electronic Resource
    Electronic Resource
    Features of volcanic tremors on Mt. Etna (Sicily) during the March–August 1983 eruption (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 929-939 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The seismic analysis of the volcanic tremors preceding and accompanying the Etnean eruption of March–August, 1983 has shown a significant variation in the spectral content before the beginning of the eruption, the tremor peaks at 1.4 and 1.6 Hz — which might be associated with the feeding pipes of the NE crater (Schick et al., 1982a) — being the dominant feature of the spectra. A model of eruption mechanism is proposed where a feeder dyke would connect the NE crater with the effusive fracture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952352
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