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  • 1
    Electronic Resource
    Electronic Resource
    Seismic Zoning of Slovenia Based on Deterministic Hazard Computations (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 171-184 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Seismic hazard, seismic zoning, Slovenia.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. Seismic hazard of the territory of Slovenia is estimated using a deterministic approach based on the computation of complete synthetic seismograms. The input data are the catalogues of earthquakes and fault plane solutions for Slovenia and surrounding regions. Structural models are defined based on available seismological and geophysical information, but are mainly constrained by surface-wave dispersion and 3-D tomographic modelling of the upper crust. Seismogenic zones are delineated considering geotectonic characteristics, fault plane solutions and distribution of earthquake hypocentres. Outside Slovenia seismogenic zones are extended up to distances from which they can considerably influence seismic hazard estimates.¶Synthetic seismograms are computed using the “receiver” structure along the entire path by normal mode summation (up to 1 Hz) for receiver sites on a 0.2 × 0.2 degrees grid and scaled to the magnitude of the earthquake allowing for spectral falloff. At each site the maximum value of horizontal velocity, horizontal displacement and design ground acceleration are considered as hazard parameter. The highest values are obtained for western Slovenia where the hazard is controlled by the strongest earthquake in the catalogue, the “Idrija” event of March 26, 1511.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001093
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  • 2
    Electronic Resource
    Electronic Resource
    A Contribution to Seismic Hazard Assessment in Croatia from Deterministic Modeling (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 185-204 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Seismic hazard, deterministic modeling, synthetic seismograms, Croatia.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Some of the elements of regional seismic hazard in Croatia are assessed by computing synthetic accelerograms at a predetermined set of sites. The input dataset consists of structural models, parameters of seismic sources, and an updated earthquake catalog. Synthetic strong-motion time series for frequencies below 1 Hz are computed on a grid of sites using the modal summation technique. The long-period hazard is described by the distribution of estimated peak values of ground displacement, velocity and acceleration, while the short-period hazard is represented by the map of design ground acceleration values (DGA). The highest values of DGA exceeding 0.35 g on the base-rock level are found in the southeastern coastal part of the country, in the greater Dubrovnik area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001094
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  • 3
    Electronic Resource
    Electronic Resource
    Simultaneous Inversion of Hypocentral Parameters and Structure Velocity of the Central Region of Madagascar as a Premise for the Mitigation of Seismic Hazard in Antananarivo (1997)
    Springer
    Pure and applied geophysics 149 (1997), S. 707-730 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Seismic velocity model, hypocenter location, Itasy, Ankaratra, Madagascar.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. —A layered velocity is obtained using arrival-time data of P and S waves from local earthquakes for the Central Region of Madagascar. A damped least-squares method is applied in the inversion of the data. The data used are 770 P-wave arrival times for 154 events which have epicenters in the region inside the Malagasy network operated by the Institut et Observatoire de Géophysique d’Antananarivo (IOGA). These data are jointly used in the inversion for the earthquake hypocenters and P- and S-wave velocity models. S waves are not used in the first step of the inversion, since their use leads to large location errors. If the error on the phase reading for the P wave is about 0.1s, for the S wave it is considerably bigger. The reference average model used here is a variant of the model given by Rakotondrainibe (1977).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050048
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  • 4
    Electronic Resource
    Electronic Resource
    Complete synthetic seismograms for high-frequency multimodeSH-waves (1991)
    Springer
    Pure and applied geophysics 136 (1991), S. 529-560 
    Details
    ISSN: 1420-9136
    Keywords: Modal summation ; broad band ; Love waves ; anelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present an efficient scheme to compute high-frequency seismograms (up to 10 Hz) forSH-waves in a horizontally stratified medium with the mode summation method. The formalism which permits the computation of eigenvalues, eigenfunctions and related integral quantities is discussed in detail. Anelasticity is included in the model by using the variational method. Phase velocity, group velocity, energy integral and attenuation spectra of a structure enable the computation of complete strong motion seismograms, which are the basic tool for the interpretation of near-source broad-band data. Different examples computed for continental structures are discussed, where one example is the comparison between the observed transversal displacement recorded at station IVC for the November 4, Brawley 1976 earthquake and synthetic signals. In the case of a magnitudeM L =5.7 earthquake in the Friuli seismic area we apply the mode summation method to infer from waveform modeling of all three components of motion of observed data some characteristics of the source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878586
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  • 5
    Electronic Resource
    Electronic Resource
    Simultaneous inversion of velocity structures and hypocentral locations: Application to the Friuli seismic area NE Italy (1992)
    Springer
    Pure and applied geophysics 138 (1992), S. 267-285 
    Details
    ISSN: 1420-9136
    Keywords: Seismic velocity ; hypocenter location ; Friuli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A layeredP- andS-wave velocity model is obtained for the Friuli seismic area using the arrival time data ofP- andS-waves from local earthquakes. A damped least-squares method is applied in the inversion. The data used are 994P-wave arrival times for 177 events which have epicenters in the region covered by the Friuli seismic network operated by Osservatorio Geofisico sperimentale (OGS) di Trieste, which are jointly inverted for the earthquake hypocenters andP-wave velocity model. TheS-wave velocity model is estimated on the basis of 978S-wave arrival times and the hypocenters obtained from theP-wave arrival time inversion. We also applied an approach thatP- andS-wave arrival time data are jointly used in the inversion (Roecker, 1982). The results show thatS-wave velocity structures obtained from the two methods are quite consistent, butP-wave velocity structures have obvious differences. This is apparent becauseP-waves are more sensitive to the hypocentral location thanS-waves, and the reading errors ofS-wave arrival times, which are much larger than those ofP-waves, bring large location errors in the joint inversion ofP- andS-wave arrival time. The synthetic data tests indicated that when the reading errors ofS-wave arrivals are larger than four times that ofP-wave arrivals, the method proposed in this paper seems more valid thanP- andS-wave data joint inversion. Most of the relocated events occurred in the depth range between 7 and 11 km, just above the biggest jump in velocity. This jump might be related to the detachment line hypothesized byCarulli et al. (1982). From the invertedP- andS-wave velocities, we obtain an average value 1.82 forV p /V s in the first 16 km depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878899
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  • 6
    Electronic Resource
    Electronic Resource
    Application of numerical wave-propagation techniques to study local soil effects: The case of Benevento (Italy) (1994)
    Springer
    Pure and applied geophysics 143 (1994), S. 513-536 
    Details
    ISSN: 1420-9136
    Keywords: Local soil effects ; wave propagation ; numerical modelling ; seismic zonation ; seismic ground motion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Many of the numerical techniques used for seismic zonation studies treat one-dimensional structural models and/or the incidence of plane polarized body waves. These techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest. In such cases a more rigorous treatment of the combined effects of the source, the path and the site response is needed. This can be accomplished with a hybrid approach combining modal summation and the finite-difference technique. To demonstrate the differences between these techniques, the ground motion in the city of Benevento (Italy) is modelled. We first compare the results obtained with one-and two-dimensional structural models for vertical incidence of plane polarized body waves. These results are then compared with those obtained with the hybrid approach for two-dimensional structural models. The comparisons have allowed us to find important differences in the response obtained with the different modelling techniques. For the same site, these differences consist of strong variations in amplitude and in the shape of the spectral amplifications. For a seismic source which is not located beneath the site, vertical incidence of waves significantly overestimates the local hazard in a laterally homogeneous structure. For a laterally heterogeneous area, we can conclude that one-dimensional modelling fails to estimate the seismic hazard, whereas for a seismic source which is not located beneath the site of interest, two-dimensional modelling with vertical incidence of plane polarized body waves may not allow reliable estimates to be made of the frequency bands at which amplifications occur. The results obtained for two-dimensional structural models are used for a zonation of the city of Benevento.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879496
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  • 7
    Electronic Resource
    Electronic Resource
    Irpinia, Italy, 1980 earthquake: waveform modelling of strong motion data (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 101 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Several strong motion records of the Irpinia (southern Italy) 1980 earthquake have been modelled for a total time duration of about 180 s with the use of the multimode summation of waves of P—SV and SH type. If waveform modelling is applied to unfiltered accelerations the best that can be done, at present, is amplitude envelope matching in time and frequency domain. The early phase of the studied event can be synthesized by 12 main episodes of different sizes, modelling the rupturing process. The space-time distribution of such episodes suggests that the rupturing process did propagate in a bilateral fashion. This model of the seismic source gives rise to synthetic velocity records which match quite well the experimental ones. To avoid the problems connected with the large instability of displacements obtained from direct numerical integration of observed accelerograms, the synthetic signals can be first used to perform acceleration or velocity fitting of experimental data; an estimate of the ground displacement above 1 Hz can then be obtained by analytical integration of the synthetic velocities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb05575.x
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  • 8
    Electronic Resource
    Electronic Resource
    Linearized waveform inversion of local and near-regional events for source mechanism and rupturing processes (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 116 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We have developed an algorithm which can, given an initial trial solution, determine simultaneously earthquake-source mechanism, hypocentre and source-time function from the inversion of broad-band waveform data of local and near-regional events (epicentral distances less than 10°).The forward modelling of the seismic ground motion is computed for frequencies up to 10 Hz by multimodal summation in layered anelastic media. The non-linear damped least-squares technique is used to minimize the difference between the theoretical and the observed seismograms in the time domain. The use of a weighting matrix and variable damping factor in each iteration avoids the problem of the ill-conditioned matrix inverse and guarantees the stability of the inverse solution. To reduce the influence of the earth model error on the inversion, for each source-receiver path the most appropriate layered earth model can be used.The algorithm has been tested against synthetic data to investigate the inversion convergence and the dependence of the solution on the fact that the assumed earth model is never equal to the true one. The synthetic tests indicate that if the earth model(s) is (are) adequate, the inversion converges rapidly to the ‘true’ solution. The sensitivity of the method to the starting model is found to be frequency dependent. The initial location can be in error by approximately the P- or S-wave wavelength and the initial source mechanism parameters can differ considerably from ‘true’model. The focal depth and source-time function depend strongly on the crustal model.Subsequently, the algorithm has been successfully applied to two events: a near-regional and a local event. The first is the 1974 March 22 event which occured in Albania, was recorded at Bari and Trieste LP stations (like WWSSN), and has been analysed using two differnt structural models based upon surface-wave dispersion measurements. The second is the Friuli event of 1987 December 27, which was recorded at five digital SP local stations, and has been analysed using a local crustal model obtained from the inversion of P- and S-wave arrival times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb03296.x
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  • 9
    Electronic Resource
    Electronic Resource
    Crust and upper mantle models along the active Tyrrhenian rim (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 7 (1995), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The volcanic complexes from the Eolian islands to the Campania/Roman regions and Tuscany further north, rest on lithospheric sectors which overlie the Adriatic continental lithosphere sinking along the Apennine-Maghrebian orogenic belt. Evidence for this stems from the melting, at mantle depth, of upper crustal materials as indicated by the widespread interaction of S-type and K-alkaline melts. The genesis of atypical magmas of the Roman Province (central-southern Italy) appears to be the result of an important block faulting and deep lithospheric rifting of the Apennine continental margin lying parallel to and above relic sinking slabs. Intermediate and deep-focus earthquakes indicate that the lithospheric slab is still seismically active under the Eolian-Calabrian area and, sporadically, at the southern end of Campania. On the other hand, in the Roman/Tuscan region, it seems to be almost inactive, few earthquakes having been located with hypocentral depths not exceeding 150 km. The analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of Tuscany and South Tyrrhenian sea, which are separated by a tensional region, which extends from Latium to Calabria. The existence of distinct lithospheric slabs along the Tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as P-wave residuals, and is confirmed by the trend of long-wavelength gravity anomalies. Bidimensional gravity models along transects in the Tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic, seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above-mentioned lithospheric slabs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1995.tb00804.x
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  • 10
    Electronic Resource
    Electronic Resource
    Site amplifications in the city of Benevento (Italy): comparison of observed and estimated ground motion from explosive sources (1998)
    Springer
    Journal of seismology 2 (1998), S. 125-143 
    Details
    ISSN: 1573-157X
    Keywords: finite differences ; lateral heterogeneities ; microzoning ; synthetic seismograms ; wave propagation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A hybrid approach is applied to construct 2-D synthetic seismograms for explosive sources. The computation of the signals has been performed with a hybrid technique, that couples the modal summation method, describing the P-SV propagation from the source to a target area, to the finite difference method, allowing the computation of the 2-D response of the target area. We use this technique to study the site response in the city of Benevento (Southern Italy). The results are compared both with those obtained for the same model, but considering an extended double-couple source and SH wave propagation and with those derived from a direct analysis of experimental data obtained during the Benevento Seismic Risk Project, funded by the Commission of European Communities. The type and depth of the source and the source-receiver distance can provide different excitations, but the response of the target area, in terms of ratios of response spectra, remains in general stable in the high frequency range (〉2 Hz). The explosive source does not excite lower frequencies and is therefore unable to provide estimates of site effects in this frequency range. We also show that it is important to consider both P-SV and SH waves when assessing site effects. Finally, a very good definition of a structural model from geological data is fundamental in order to explain the observed data in the time domain. The observed data validate our synthetic modelling for evaluating the site effects and for a tentative seismic microzonation of the city of Benevento.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008052204879
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