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  • 1
    Electronic Resource
    Electronic Resource
    Statistical analysis of earthquake activity at Etna volcano (March 1981 eruption) (1985)
    Springer
    Pure and applied geophysics 123 (1985), S. 697-705 
    Details
    ISSN: 1420-9136
    Keywords: Volcanic earthquakes ; statistical analysis ; Mt. Etna
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Seismic activity that preceded, accompanied, and followed the 17–23 March 1981 Etnean eruption has been statistically analyzed. On the grounds of both time evolution of seismicity and catalogue completeness, three time intervals have been defined (12 February–2 March, 12–17 March, 19–31 March) and for each of these periods both the “b” coefficient of theGutenberg-Richter's (1956) relationship and the “E” parameter of the cluster size (Shlien andToksoz, 1970) have been calculated. No significant variations were observed between the first and third periods, while lower values of bothb andE coefficients were found in the second one. These findings might indicate that changes in the seismicity features occur just before the eruption start. Small but fast variations in the stress field acting on the volcano might originate this type of seismic activity, while the importance of the tectonic control on volcanic phenomena seems to be confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878403
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  • 2
    Electronic Resource
    Electronic Resource
    Scaling of peak ground motions from digital recordings of small earthquakes at Campi Flegrei, southern Italy (1988)
    Springer
    Pure and applied geophysics 126 (1988), S. 37-53 
    Details
    ISSN: 1420-9136
    Keywords: scaling of peak ground motions ; volcanic microearthquakes ; source parameters ; high frequency attenuation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The dependence of peak ground acceleration and velocity on seismic moment is studied for a set of small earthquakes (0.7〈M L〈3.2) recorded digitally at distances of a few km in the Campi Flegrei volcanic area near Naples, Italy, during the ground uplift episode of 1982–1984. Numerical simulations, using the ω-square spectral model with constant stress drop and ane −πkf high frequency decay, fit well both the velocity and acceleration data for an averagek=0.015. The observed ground motions in the 1–24 Hz frequency band appear to consist of radiation from simple sources modified only slightly by attenuation effects. Moreover, the scaling of peak values agrees closely with those determined in nonvolcanic areas, once the difference in stress drop is taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876913
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  • 3
    Electronic Resource
    Electronic Resource
    Constraints on the shallow crustal model of the Northern Apennines (Italy) from the analysis of microearthquake seismic records (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A joint study of microearthquake source and medium parameters was carried out by analysing a seismic sequence that occurred in the Tuscan Emilian Apenninic region. Signal processing and graphic techniques were applied to study the amplitude and polarization of wave motion and thus identify the main and secondary body-wave arrivals on the seismic records.The evidence for similar waveforms (denoted as ‘similar events') in a micro-earthquake subset allowed application of a non-linear technique, which provided the accurate relative location of the events. Microearthquakes occurred within the shallow sediments (average depth of 3.5 km), and all appeared to be concentrated in a small volume of about 1 km3. The composite fault mechanism of the ‘similar events’ was computed by non-linear inversion of P-polarity readings. The maximum-likelihood solution appeared to be well constrained, and indicated a normal-faulting mechanism with the T axis approximately oriented in a northerly direction.Interpretation of several secondary arrivals was performed by direct modelling of traveltimes and wave-motion amplitudes using a double-couple point-source model. Green's functions in a layered medium were computed using two different methods, based on ray theory (Farra 1990) and discrete wavenumber representation of the wavefield (Bouchon 1981). The study of secondary arrivals indicates a depth of 11-12 km for the top of the crystalline pre-Tertiary basement. This estimate concerns a region located at around 3-6 km from the epicentres of the ‘similar events', along the N290°E direction. The modelling of arrival times for an S-to-P converted phase at the basement discontinuity suggests an increase of about 10 per cent in the basement seismic-wave velocity (VP˜˜ 6.9 km s-1), or, equivalently, an increase of the VP to VS ratio in the upper sediments. The increments were defined with respect to an existing reference model by AGIP (Italian Petroleum Agency). Recordings at the Minerbio station (MIN) (located about 40 km SE of the epicentral area) show converted/reflected phases at shallow crustal discontinuities and wave-resonance phenomena. These path effects appear repeatedly on seismic records independently of the size of earthquakes within the magnitude range considered. Waveform and traveltime modelling of these secondary arrivals provide further constraints on the depth and velocity of main-structure discontinuities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb01843.x
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  • 4
    Electronic Resource
    Electronic Resource
    Fault mechanisms from near-source data: joint inversion of S polarizations and P polarities (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 104 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We propose a non-linear inversion method for studying the earthquake mechanism by combining the information carried by both S-wave polarizations and P-wave polarities from near-source records. The posterior probability of parameters (strike, dip and slip fault angles) for the given observational data sets is computed by using a Bayesian approach. The conditional probability density function of S polarizations given a model parameter set is defined assuming a Gaussian distribution for the expected errors. The P polarity information is taken into account in the form of a prior probability density function, which has been defined according to Brillinger, Udias & Bolt (1980). The method is based on the estimate by an exhaustive search of the posterior probability of model parameters. This probability is then represented by its projection on plane sections in the model space. This enables one to locate the maximum likelihood solutions, and to get a reliable estimate of the parameter correlation and resolution. Numerical examples and data analysis show that the addition of a few S polarizations to a P polarity data set greatly improves the resolution on the fault parameters.The proposed method is suitable to study the low-magnitude seismicity in active tectonic and volcanic areas which are monitored by local networks as the use of three-component sensors becomes more systematic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb05692.x
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  • 5
    Electronic Resource
    Electronic Resource
    Modelling of ground acceleration in the near source range: the case of 1976, Friuli earthquake (M = 6.5), northern Italy (1997)
    Springer
    Journal of seismology 1 (1997), S. 305-319 
    Details
    ISSN: 1573-157X
    Keywords: kinematic source model ; strong ground motion ; directivity effect ; source geometry effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A mixed statistical-deterministic model of earthquake rupture is developed for evaluating the strong ground motion in the near source range (receiver distance comparable to the fault length). The source parametrization is based on the k-square model and the propagation is computed by asymptotic Green's functions. The method is applied to the case of 1976, Friuli earthquake (M = 6.5) in northern Italy which occurred on a low-dip thrusting fault. Acceleration records at 29 stations are computed for 100 simulations of rupture histories. The mean value map of peak ground accelerations shows clearly a maximum to the south due to the inner geometry and directivity of the source. The variation of the estimated PGA versus the epicentral distance is strongly dependent on azimuth and is not decreasing monotonically. The comparison of these curves with those predicted by empirical acceleration–distance relationships shows discrepancies in the near source distance range. This study shows the importance of considering the complexity of the source rupture process for strong motion estimate in the near source range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009766214032
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  • 6
    Electronic Resource
    Electronic Resource
    High frequency strong ground motion modelling in the Catania area associated with the Ibleo-Maltese fault system (1999)
    Springer
    Journal of seismology 3 (1999), S. 279-288 
    Details
    ISSN: 1573-157X
    Keywords: complex source model ; site effect ; strong motion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A hybrid statistical-deterministic approach has been applied to estimate strong ground motion parameters (PGA, spectral ordinates) in South-Eastern Sicily for a M = 7 earthquake. A number of 100 different rupture processes have been simulated along a composite fault system representing two segments of the Ibleo-Maltese fault scarp. Map at regional scale of mean PGA in the 0.5–20 Hz frequency band shows highest values (0.4–0.5 g) nearby and North of Catania, due to a dominant directivity effect. The COV parameter, which expresses the variability of PGA values as a function of source complexity, is higher in the region nearby and South of the town of Augusta, where, depending on the rupture history, rather large PGA values can be observed (〉0.4 g). PGA attenuation curves suggest that an azimuthal variation could be related to the source extent and directivity. The response and pseudo acceleration spectra are computed for different sites in the town of Catania including an approximate 1D site response. Ground motion amplification effects at high frequency (5–20 Hz) are produced by thin shallow layer of soft clay, loose pyroclastites and fill. We observe small amplification effects, in the frequency ranges 2–3 Hz and 5–10 Hz, in sites where recent alluvia reach a thickness of some tens of meters. Otherwise, sites located on outcrops of massive lavas show moderate attenuation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009857730064
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  • 7
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    Fault mechanisms from near-source data: joint inversion of S polarizations and P polarities (2007)
    Oxford University Press
    Details
    Publication Date: 2007-04-02
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 8
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    Source parameter scaling and radiation efficiency of microearthquakes along the Irpinia fault zone in southern Apennines, Italy (2014)
    American Geophysical Union
    Details
    Publication Date: 2014-04-01
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 9
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    The Effectiveness of a Distant Accelerometer Array to Compute Seismic Source Parameters: The April 2009 L'Aquila Earthquake Case History (2011)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2011-02-01
    Description: The 6 April 2009 Mw 6.3 L'Aquila earthquake, central Italy, has been recorded by the Irpinia Seismic Network (ISNet) about 250 km southeast of the epicenter. Up to 19 three-component accelerometer stations could be used to infer the main source parameters with different seismological methods. We obtained an approximate location of the event from arrival times and array-based back-azimuth measurements and estimated the local magnitude (6.1) from an attenuation relation for southern Italy. Assuming an omega-square spectral model, we inverted S-wave displacement spectra for moment magnitude (6.3), corner frequency (0.33 Hz), stress drop (2.5 MPa), and apparent stress (1.6 MPa). Waveform modeling using a point source and an extended-source model provided consistent moment tensors with a centroid depth around 6 km and a prevalently normal fault plane solution with a dominant directivity toward the southeast. The relatively high corner frequency and an overestimated moment magnitude of 6.4 from moment tensor inversions are attributed to the rupture directivity effect. To image the rupture geometry, we implemented a beamforming technique that back-projects the recorded direct P-wave amplitudes into the earthquake source region. A northwest-southeast striking rupture of 17 km length is imaged, propagating with an average velocity up to 3 km/s. This value is significantly higher than our estimate of 2.2 km/s from S-wave spectra. Our case study demonstrates that the use of array techniques and a dense accelerometer network can provide quick and robust estimates of source parameters of moderate-sized earthquakes located outside the network.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 10
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    Test of a Threshold-Based Earthquake Early-Warning Method Using Japanese Data (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-06-01
    Description: Most of existing earthquake early-warning systems are regional or on-site systems. A new concept is the integration of these approaches for the definition of alert levels and the estimation of the earthquake potential damage zone (PDZ). The key element of the method is the real-time, simultaneous measurement of initial peak displacement (Pd) and period parameter (τc) in a 3-s window after the first P-wave arrival time at accelerometer stations located at increasing distances from the epicenter. As for the on-site approach, the recorded values of Pd and τc are compared to threshold values, which are set for a minimum magnitude M 6 and instrumental intensity IMM VII, according to empirical regression analysis of strong-motion data from different seismic regions. At each recording site the alert level is assigned based on a decisional table with four entries defined by threshold values of the parameters Pd and τc. A regional network of stations provides the event location and transmits the information about the alert levels recorded at near-source stations to more distant sites, before the arrival of the most destructive phase.We present the results of performance tests of this method using ten M〉6 Japanese earthquakes that occurred in the period 2000–2009 and propose a very robust methodology for mapping the PDZ in the first seconds after a moderate-to-large earthquake. The studied cases displayed a very good matching between the rapidly predicted earthquake PDZ inferred from initial P-peak displacement amplitudes and the instrumental intensity map, the latter being mapped after the event, using peak ground velocity and/or acceleration, or from field macroseismic surveys.Online Material: Animated GIF files of simulations of the threshold-based method.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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