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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the Temporal Occurrence of Seismicity at Deception Island (Antarctica). A Nonlinear Approach (1997)
    Springer
    Pure and applied geophysics 149 (1997), S. 553-574 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Correlation dimension, Hurst exponent, point process, seismicity, Weibull distribution.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Deception Island is characterized by small magnitude local events with constant energy flux and very low stress drop. To obtain information about its origin, an interevent time series of 546 events, corresponding to an observational period of two month, has been analyzed. From a statistical point of view, data satisfies a Weibull distribution and presents clustering. A rescaled range analysis reveals that data are not independent, i.e. have memory, and the correlation dimension saturates at 2.2; as a consequence, the system can be modeled as a nonlinear iterative equation with three degrees of freedom that presents chaotic behavior. Taking into account that the average interevent time is of the order of 130 minutes, too short to be only due to tectonic activity, the above results indicate that some other mechanism may coexist with the regional tectonic one. According to several geological and geophysical observations, we suggest that most of the local events may be originated by pressure waves generated by a sudden change of phase, of sea and fresh water infiltrated into the main fractures and faults and also from shallow and confined water-saturated layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050041
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  • 2
    Electronic Resource
    Electronic Resource
    New Evidence of Azimuthal Variations at Campi Flegrei: Attenuation and Predominant Frequency (1997)
    Springer
    Pure and applied geophysics 150 (1997), S. 285-304 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Campi Flegrei, attenuation, predominant frequency, azimuthal variations.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —In this paper we have determined apparent Q from body-wave dispersion and a spectral ratio method for the Campi Flegrei area. A contour map of azimuthal variations of apparent Q (ranging from Q = 4 to Q = 40) reveals that the lower Q (higher attenuation) corresponds to an area that includes the Solfatara Crater (with active fumaroles), near the site of maximum uplift produced during the bradyseismic crisis of 1984, and just over the site evidencing the presence of a magmatic body. A strong azimuthal variation of the predominant frequency of the first pulse of the P wave has been found and is interpreted in terms of a vertical travel time in a surficial resonant layer (∼ 1 km thick) over a halfspace. The attenuation maps, the interpretation of the resonant frequencies, and the additional information provided by the P-wave velocity suggest the presence of a circular structure in the area. Not only does the distribution of the thickness of the resonant layer (obtained through the estimation of the contribution of different harmonics) show the circular structure, but it also agrees with the presence of a thin layer of lighter sediments, determined by means of a microgravimetric study, and with the total magnetic map, previously obtained for this area. The results of the azimuthal variation provide new evidence of the structure that can be used to improve the knowledge of the area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050077
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of seismic dynamical systems (1998)
    Springer
    Journal of seismology 2 (1998), S. 159-171 
    Details
    ISSN: 1573-157X
    Keywords: chaos ; dynamical systems ; Hurst exponent ; stochasticprocess ; time series
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A procedure is presented for the analysis of complex stationary time series for which the Fourier power spectra reveals broadband noise or broadened pulses. We first determine the Hurst exponent from which we may know whether the time series under study is mainly random or if the data points present correlations. If the data are correlated, a chaotic analysis will reveal whether they may be interpreted as a low dimensional nonlinear system (defined by a low correlation dimension and a finite and positive Kolmogorov entropy and largest positive Lyapunov exponent) or as a stochastic process. We have studied three kind of temporal series: inter-event time series of infrasonic pulses recorded at Stromboli volcano, and, S-coda waves and microseisms, that have been recorded at the eastern Pyrenees. Results show that microseisms and Coda waves can be modeled as a low dimensional deterministic system, Correlation dimensions 2.3, 3.2, respectively. At the contrary infrasonic has resulted stochastic. This chaotic character can be attributed to the medium properties. Coda waves with scattering through a fractal distribution of scatters or to multiple reflection inside resonators (for example sedimentary basins) and microseisms as a propagation of wave guide of variable cross section which have the same temporal characteristics as a nonlinear forced oscillator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008007328969
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    Paper (German National Licenses)
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