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  • 1
    Electronic Resource
    Electronic Resource
    Seismic sources and attenuation properties at the Campi Flegrei volcanic area (1987)
    Springer
    Pure and applied geophysics 125 (1987), S. 883-917 
    Details
    ISSN: 1420-9136
    Keywords: Campi Flegrei ; Volcanic earthquakes ; Attenuation ; Source parameters ; Moment tensor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Microearthquake digital data collected at Campi Flegrei during the recent (1982–1985) ground uplift episode have been analyzed in order to infer source and medium seismic properties. The main results obtained from these analyses are: 1. Hypocenter distribution and the size of the seismic zone do not change with time and do not depend on the ground uplift rate. Events occurred clustered in time with no simple causal relations between the cluster occurrences and their energy. 2. Anelastic attenuation does not depend strongly on frequency, showing a constant pattern at high frequencies. The observed values of low and high frequency attenuation, due to the short source receiver distances, do not seriously affect the spectral content of signals radiated by the sources. 3. A constant Brune stress drop pattern (∼4–5 bars) as a function of seismic moment is observed. This indicates that the manner of fracturing is almost independent on magnitude of earthquakes (hypothesis of self-similarity (Aki, 1967)). Seismic processes in a prefractured medium can explain the observed small stress drop values. 4. Focal mechanisms from moment tensor estimates show that radiation patterns are mostly well interpreted in terms of double couple source models. 5. The scaling of peak ground motion parameters (A max andV max vs seismic moment) can be explained by an ω2 source model (constant stress drop) multiplied by an exponential function with a small decay parameter, which takes into account the measured attenuation. These results support the hypothesis of earthquakes generated by simple shear fractures along prefractured structures as a response to changes in the stress field due to the ground deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879360
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  • 2
    Electronic Resource
    Electronic Resource
    1-D P-velocity Models of Mt. Vesuvius Volcano from the Inversion of TomoVes96 First Arrival Time Data (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 1643-1661 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —We applied a revised version of the 1-D τ–p inversion method to first P-arrival times from the active seismic experiment performed at Mt. Vesuvius (southern Italy) in 1996 (TomoVes96 Project). The main objective of this work is to obtain 1-D velocity models of Mt. Somma-Vesuvius volcano complex and surrounding area. Moreover we show that combining the 1-D information we provide a reliable 2-D initial model for perturbative tomographic inversions. Seismic and geological surveys suggest the presence of a refractor associated with the contrast between carbonate basement and volcanic/alluvial sediments; synthetic simulations, using a realistic topography and carbonate top morphology, allowed us to study the effect of topography on the retrieved velocity models and to check that the 1-D τ–p method can also approximately retrieve the refractor depth and velocity contrast. We analysed data from 14 on-land shots recorded at stations deployed along the in-profile direction. We grouped the obtained models in three subsets according to the geology of the sampling area: Models for carbonate outcrop area, models for the Campanian Plain surrounding the volcano edifice and models for Mt. Somma-Vesuvius volcano complex. The found 1-D P-velocity models show important vertical and lateral variations. Very low velocities (1.5–2.5 km/s) are observed in the upper 200–500 m thick shallow layer. At greater depths (3 km is the maximum investigated depth) P velocities increase to values in the range of 4–6 km/s which are related to the presence of the carbonatic basement. Finally we interpolated the 1-D models to demonstrate an example of misfit for a 2-D interpolated model whose residuals are confined in a narrow band around zero.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001054
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  • 3
    Electronic Resource
    Electronic Resource
    Q c of three component seismograms of volcanic microearthquakes at Campi Flegrei volcanic area — Southern Italy (1985)
    Springer
    Pure and applied geophysics 123 (1985), S. 683-696 
    Details
    ISSN: 1420-9136
    Keywords: Q ; code waves ; volcanic earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Digital recordings of three component microearthquake codas from shallow seismic events in the volcanic region of Campi Flegrei — Southern Italy — were used with an automatic technique to calculate the attenuation factorQ c (codaQ) in the hypothesis of singleS toS backscattering. Results show the same value ofQ for each of the three components. This result is interpreted as due to isotropicS wave radiation pattern. A check of the coda method was performed using a single station method based on simple assumptions on the direct SH wave spectrum. Single stationQ was averaged over the stations and over the earthquakes. Results show that the two methods lead to comparable results. A frequency dependence quite different from that evaluated in active tectonic regions was found for coda attenuation, comparable to other volcanic areas throughout the world. This is interpreted as due to the presence of magma that affects anelasticity and scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878402
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  • 4
    Electronic Resource
    Electronic Resource
    A detailed analysis of microearthquakes in western Crete from digital three-component seismograms (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 110 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Seismological data collected during the summer of 1988 are presented and analysed to discuss the microearthquake deformation in western Crete (Greece). The experiment consisted, in a dense network, of 34 stations (5 km interstation spacing) among them 13 three-component digital stations. The seismicity is essentially localized between 0 and 15 km and suggests a deformation of Crete decoupled from the subducting plate which shows a very low seismicity. The fault plane solutions are constrained by combining the information from P-wave polarities with that from horizontal directions of S-wave polarizations using the probabilistic approach developed by Zollo & Bernard (1991). Among the 16 fault plane solutions calculated, there are essentially two families: normal faulting on planes oriented NS and strike-slip faulting. Both have a horizontal SE to NE oriented tension axis. The mean direction of the T-axis confirms the E-W extension of this part of the Hellenic arc where observations at larger scale are available (active and Holocene fault scarps and fault plane solution of one teleseismic event). Observations of elliptical polarizations of S-waves at two stations suggest the presence of a shallow low-velocity anisotropic layer. Assuming a model of vertical cracks, this anisotropy would imply that the cracks be oriented N145–170d̀. This direction of aligned cracks is consistent with the regional E–W oriented extension as determined by the fault plane solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00879.x
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  • 5
    Electronic Resource
    Electronic Resource
    Source investigation of a small event using empirical Green's functions and simulated annealing (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We propose a two-step inversion of three-component seismograms that (1) recovers the far-field source time function at each station and (2) estimates the distribution of co-seismic slip on the fault plane for small earthquakes (magnitude 3 to 4). The empirical Green's function (EGF) method consists of finding a small earthquake located near the one we wish to study and then performing a deconvolution to remove the path, site, and instrumental effects from the main-event signal.The deconvolution between the two earthquakes is an unstable procedure: we have therefore developed a simulated annealing technique to recover a stable and positive source time function (STF) in the time domain at each station with an estimation of uncertainties. Given a good azimuthal coverage, we can obtain information on the directivity effect as well as on the rupture process. We propose an inversion method by simulated annealing using the STF to recover the distribution of slip on the fault plane with a constant rupture-velocity model. This method permits estimation of physical quantities on the fault plane, as well as possible identification of the real fault plane.We apply this two-step procedure for an event of magnitude 3 recorded in the Gulf of Corinth in August 1991. A nearby event of magnitude 2 provides us with empirical Green's functions for each station. We estimate an active fault area of 0.02 to 0.15 km2 and deduce a stress-drop value of 1 to 30 bar and an average slip of 0.1 to 1.6 cm. The selected fault of the main event is in good agreement with the existence of a detachment surface inferred from the tectonics of this half-graben.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb06022.x
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  • 6
    Electronic Resource
    Electronic Resource
    Source parameters of microearthquakes at Phlegraean Fields (Southern Italy) volcanic area
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 47 (1987), S. 25-42 
    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(87)90064-1
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  • 7
    Electronic Resource
    Electronic Resource
    Rupture characterization of a low magnitude earthquake of central Apennines (Italy)
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 82 (1994), S. 157-165 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0031-9201(94)90086-8
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  • 8
    Electronic Resource
    Electronic Resource
    Seismic coda Q and turbidity coefficient at the Phlegraean Fields volcanic area: Preliminary results (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 219-224 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Digital recordings of microearthquake codas from shallow seismic events in the Phlegraean Fields region (south-central Italy) were used to calculate the attenuation factor Qc. A quite unusual frequency dependence was found for the coda attenuation comparable to Hawaii pattern of Qc. This is interpreted as due to the presence of magma that increases the amount of anelasticity. Amount of scattering at Phlegraean Fields was estimated through the « turbidity » coefficient (Dainty model), that shows a high degree of scattering due to inhomogeneities as compared to Hawaii. Probably this is due to the greater crustal thickness of Phlegraean Fields with respect to Hawaii that produces more scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01961551
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  • 9
    Electronic Resource
    Electronic Resource
    Space-time distribution of small earthquakes at Phlegraean Fields, south-central Italy (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 201-207 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A preliminary statistical analysis of the space-time distribution of small seismic events in the volcanic area of Phlegraean Fields, south-central Italy, was done on the basis of a catalogue of earthquakes recorded by the local seismic stations in the period January 1, December 31, 1983. The non-random character of the sequence has been tested by matching the observed time-dstribution of seismic events with the theoretical Poisson process. A clustered occurrence of seismic events seems to be the main cause of the departure from a Poisson process as the inter-arrival times distribution clearly shows. Furthermore, the non-random behaviour of the events space-time distribution mainly due to quiescient and clustered recursive seismic phases could be studied by using the method proposed byVon Seggern et al. (1981). The analysis and the space-time diagrams confirm the swarm-type character of the entire seismic sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01961549
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  • 10
    Electronic Resource
    Electronic Resource
    Error analysis in hypocentral locations at Phlegraean Fields (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 209-218 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The location reliability of the earthquakes occurred at Phlegraean Fields has been analyzed, and the theoretical errors, inferred from the diagonal elements of the covariance matrix, have been estimated. Using only first P-phase arrivals to the local network (22 stations) and assuming a reading error of 0.05 sec., the average error on the spatial coordinates is estimated to be of the order of 0.2 km. Shallow events (depth〈1 km) are very poorly constrained in depth at the borders of the network. The use of both P and S arrival times, recorded by a smaller three component network (10 stations), improves the depth determination. Further analysis has been performed on a set of about 350 selected earthquakes, using two different velocity models. Differences in depth considerably greater than the theoretical errors, and showing highly different patterns have been found. Tests with artificial events, randomly distributed in space, indicate that the observed depth distribution is essentially due to the used velocity model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01961550
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