Seismic moment tensor resolution by waveform inversion of a few local noisy records-II. Application to the Phlegraean Fields (Southern Italy) volcanic tremors

Cespuglio, G.; Campus, P.; Šı́lený, Jan

doi:10.1111/j.1365-246x.1996.tb04694.x

Cited by 23 publications

(8 citation statements)

References 27 publications

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“…Tests done on synthetic data have also shown that the inversion results are stable until the noise in the data is less than 20% of the maximum amplitude CESPUGLIO et al, 1996). The solutions are stable even when few stations are used (SILENY et al, 1992).…”

Section: Earthquake Source Processesmentioning

confidence: 86%

Three Decades of Seismic Activity at Mt. Vesuvius: 1972?2000

Natale

Kuznetzov

Kronrod

et al. 2004

Pure and Applied Geophysics

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We analyse the seismic catalogue of the local earthquakes which occurred at SommaVesuvius volcano in the past three decades . The seismicity in this period can be described as composed of a background level, characterised by a low and rather uniform rate of energy release and by sporadic periods of increased seismic activity. Such relatively intense seismicity periods are characterised by energy rates and magnitudes progressively increasing in the critical periods. The analysis of the b value in the whole period evidences a well-defined pattern, with values of b progressively decreasing, from about 1.8 at the beginning of the considered period, to about 1.0 at present. This steady variation indicates an increasing dynamics in the volcanic system. Within this general trend it is possible to identify a substructure in the time sequence of the seismic events, formed by the alternating episodes of quiescence and activity. The analysis of the source moment tensor of the largest earthquakes shows that the processes at the seismic source are generally not consistent with simple double-couples, but that they are compatible with isotropic components, mostly indicating volumetric expansion. These components are shown to be statistically significant for most of the analysed events. Such focal mechanisms can be interpreted as the effect of explosion phenomena, possibly related to volatile exsolution from the crystallising magma.The availability of a reduced amount of high quality data necessary for the inversion of the source moment tensor, the still limited period of systematic observation of Vesuvius micro-earthquakes and, above all, the absence of eruptive events during such interval of time, cannot obviously permit the outlining of any formal premonitory signal. Nevertheless, the analysis reported in this paper indicates a progressively evolving dynamics, characterised by a generally increasing trend in the seismic activity in the volcanic system and by a significant volumetric component of recent major events, thus posing serious concern for a future evolution towards eruptive activity.

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Section: Earthquake Source Processesmentioning

confidence: 86%

Three Decades of Seismic Activity at Mt. Vesuvius: 1972?2000

Natale

Kuznetzov

Kronrod

et al. 2004

Pure and Applied Geophysics

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“…(d) The source mechanism obtained for case (b) with errors. and Cespuglio et al (1996). They found that, for most of the events, there is a dominance of double-couple components.…”

Section: Campi Flegrei and Vesuviomentioning

confidence: 99%

Monitoring volcanic and geothermal areas by full seismic moment tensor inversion: are non-double-couple components always artefacts of modelling?

Panza

Saraò

2000

Geophysical Journal International

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Non‐double‐couple mechanisms in volcanic environments are indicators of local modifications of the stress field induced by dyke injection, high fluid pressure or by thermal cooling. However, the possible biasing effects of wave propagation in structurally complicated regions, the presence of noise, or inappropriate station coverage can make the identification of non‐double‐couples as true source phenomena uncertain. In this paper we review possible sources of false non‐double‐couples, and we estimate the reliability of the non‐double‐couple solutions on the basis of an error analysis that includes the variance of the modelling and of the noise in the data. Our analysis of synthetic and real data shows that we can identify, within confidence levels of 99 and 95 per cent, respectively, spurious non‐double‐couples due to inadequate station coverage, to noise in the data and to inadequacies of the structural model. Real data analyses must be preceded by synthetic tests in order to define the lower limits from which the non‐double‐couple components can be considered statistically significant at a given confidence level.

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“…Tests done on synthetic data have shown that the inversion results are stable until the noise in the data is less than 20 per cent of the maximum amplitude (Sileny et al . 1996; Cespuglio et al . 1996).…”

Section: Moment Tensor Inversionmentioning

confidence: 99%

Non-double-couple mechanisms in the seismicity preceding the 1991-1993 Etna volcano eruption

Saraò¹,

Panza²,

Privitera³

et al. 2001

Geophysical Journal International

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Summary The temporal evolution of the complete source moment tensor is investigated for 28 earthquakes that occurred at Mt Etna in the period August 1990–December 1991 preceding the biggest eruption of the last three centuries. We perform several tests to check the robustness of the results of inversion considering different frequency ranges and different groups of stations. As well as the selection of good‐quality data, the error analysis, statistically significant at the 95 per cent confidence level, is employed to validate the findings of the inversion and to distinguish between physical solutions and artefacts of modelling. For events between 0.3 and 10 km depth, strike‐slip mechanisms prevail on normal, inverse and dip‐slip mechanisms; this is possibly due to the dyke‐induced stress dominating the overall stress field at the surface, producing a continuous switch of the tensile and compressive axes. The regional E–W tension prevails at depth, as indicated by the prevalence of normal mechanisms. An increment of the non‐double‐couple components is observed immediately before the eruption and can be related to movements of fluids, even though, for some events, the complex interaction between tectonic stress and volcanic activity cannot be excluded. The source time functions retrieved are in general simple and short but some show complexities, as one would expect in volcanic seismicity. From the seismic scalar moment found, we extrapolate an empirical moment–magnitude relation that we compare with other relations proposed for the same area and computed for the duration magnitude and the equivalent Wood–Anderson magnitude.

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Seismic moment tensor resolution by waveform inversion of a few local noisy records-II. Application to the Phlegraean Fields (Southern Italy) volcanic tremors

Cited by 23 publications

References 27 publications

Three Decades of Seismic Activity at Mt. Vesuvius: 1972?2000

Three Decades of Seismic Activity at Mt. Vesuvius: 1972?2000

Monitoring volcanic and geothermal areas by full seismic moment tensor inversion: are non-double-couple components always artefacts of modelling?

Non-double-couple mechanisms in the seismicity preceding the 1991-1993 Etna volcano eruption

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