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  • 1
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    Waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model (1992)
    In:  Geophys. J. Int., Dordrecht, National Academy of Sciences of the USA, vol. 109, no. 4, pp. 259-274, pp. TC5003, (ISSN: 1340-4202)
    Details
    Publication Date: 1992
    Keywords: Earth model, also for more shallow analyses ! ; Seismology ; Moment tensor ; Inversion ; GJI
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
    Electronic Resource
    Electronic Resource
    Waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 109 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: In the inversion scheme of high-frequency seismograms, recorded by a local network, we have developed the unconstrained moment tensor description to study weak events which are believed to reflect small-scale complexities of the tectonic structure. In order to allow the source mechanism to change with time each moment tensor component has its own time history. In the inversion, the measure of the similarity between the synthetic seismograms and the observed records is obtained by minimizing the norm L2 of their difference. The initial synthetic seismograms are constructed by summing a set of time-dependent functions, named base functions. These base functions are computed by normal mode summation for a discrete set of source depths and for two structural models, considered to represent acceptable extremes for the region under study. In the course of the inversion, using a linear interpolation, new base functions are computed for intermediate values of the starting depths and structures. Thereafter new synthetic seismograms are computed and compared with the observed records until the convergence is reached, within some pre-assigned threshold for the norm L2.The method has been tested by treating, as ‘observed’records, synthetic seismograms (both displacement and velocity) generated for instantaneous and finite duration sources. The ‘observed’ records have been computed for two structures: one belonging to the structural range within which the base functions were computed, the other lying outside this range. Random noise has been superimposed on the records.When inverting synthetic records computed for a structure contained within the range of interpolation for the base functions, the full moment tensor is retrieved satisfactorily (provided that the noise level does not exceed about 20 per cent). For records computed for a structure lying outside this range a spurious volumetric part of the moment tensor appears. However, if the volumetric part of the moment tensor is removed, the source time function can be reconstructed satisfactorily, and the source mechanism can be determined from the deviatoric part of the moment tensor.The procedure has been applied to vertical component seismograms recorded in the Friuli (NE Italy) area for the ML= 2.9 event of 1987 December 27. The retrieved source mechanism is in agreement with the distribution of the few first arrival polarities available and the source time function indicates a possible multiple rupture process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00097.x
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Seismic moment tensor resolution by waveform inversion of a few local noisy records—II. Application to the Phlegraean Fields (Southern Italy) volcanic tremors (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Seismic sources with non-double-couple (non-DC) components are frequently observed in volcanic and geothermal areas. This suggests that the non-DC components may be generated by phenomena such as movements of magmatic fluids under high pressure and intrusions of dykes, which characterize volcanic areas and are believed to be responsible for volcanic tremors.Several volcanic tremors from the Phlegraean Fields, Southern Italy, have been processed with the waveform inversion method, which allows us to estimate the error on the source mechanism and on the source time function due to the noise present in the seismograms, the hypocentre mislocation and, in a simplistic way, an improper structure modelling.The events treated are examples of the seismicity accompanying the upward bradyseism of the area in 1984, and the following downward bradyseism in 1986. Significant non-DC components, i.e. a volumetric part and a compensated linear vector dipole (CLVD), are found in the mechanism, which indicates movement of magmatic fluids in the area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb04694.x
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Seismic moment tensor resolution by waveform inversion of a few local noisy records—I. Synthetic tests (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A theory is described that takes into account the effects of the random noise contained in seismic records, the mislocation of the hypocentre and the inaccurate knowledge of the velocity structure, while estimating the error affecting the mechanism and the source time function determined by waveform inversion of noisy records. Assuming Gaussian errors, the variance of the forward model error is defined and then transformed into confidence regions of eigenvalues and eigenvectors of the moment tensor and into error bars of the source time function. The method allows us to treat point sources, composed of a few subevents, either acting simultaneously or delayed in time. Therefore, in a series of synthetic tests, we investigate separately the effects of the noise level, the mislocation of the hypocentre and the inaccurate knowledge of the medium on the resolution of the two parts of a focus, composed of a double-couple (DC) and a volumetric (V) source, a general case that we find in volcanic areas.The crucial effect of the recording network geometry on the mechanism resolution is confirmed and quantitatively estimated for both the vertical component and the three-component configuration of the network.Our goal is to apply this method to the investigation of the reliability of the retrieval of the focal mechanism and the time function associated with events of low magnitude (Md〈4) recorded by local stations, both in tectonic and in volcanic areas. Special attention is devoted to volcanic areas, where the non-double-couple components of the source may reveal the existence of complex fracture processes, which are due to fluid movements in the crust
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb04693.x
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Seismic monitoring of explosions: a method to extract information on the isotropic component of the seismic source (1997)
    Springer
    Journal of seismology 1 (1997), S. 205-218 
    Details
    ISSN: 1573-157X
    Keywords: moment tensor ; waveform inversion ; modal summation ; explosions ; monitoring ; lateral heterogeneity ; point source ; source time function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The design of a monitoring system for detecting explosions is a very topical problem, both for routine data processing at seismological observatories as well as for the monitoring of a Comprehensive Test Ban Treaty. In this framework it is desirable to have the possibility to quantify the presence of the isotropic component in the seismic source. For this purpose a method is presented, which is based on waveform inversion for the full moment tensor retrieval. The method inverts either full waveforms or separate seismic phases and returns the mechanism and time history of a point source. Moreover, it allows to redefine the hypocentral depth of the event and, in a simplistic way, to optimize the structural model as well. In order to model strong laterally heterogeneous structures, different pairs of structural models can be used for each source-receiver path. The source is decomposed into a volumetric part (V), representing an explosive or implosive component, and into a deviatoric part, containing both the double couple (DC) and the compensated linear vector dipole (CLVD) components. The method is applied to an area in central Switzerland and to the network of the Swiss Seismological Service. The events of interest include both earthquakes and explosions. Despite some modelling inadequacies of the source-time function, the explosions can be well identified with the inverted isotropic component in the source, as long as the number of stations used for the inversion is larger than three. The results of the inversion are better for large epicenter-station distances of the order of 40–90 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009781722363
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Waveform inversion of weak vrancea (Romania) earthquakes (1996)
    Springer
    Studia geophysica et geodaetica 40 (1996), S. 367-380 
    Details
    ISSN: 1573-1626
    Keywords: source mechanism ; Vrancea region ; moment tensor ; waveform inversion ; modal summation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Summary The inversion of high-frequency seismograms is performed to retrieve source mechanisms, hypocentral depths and source time functions of two weak Vrancea earthquakes (ML=3.3), one that occurred in the crust, the other in the lithospheric part of the mantle. The digital waveforms recorded by the local Romanian network are used. Synthetic seismograms are computed by the modal summation method, using the point source approximation, for horizontally layered anelastic media. For each source-to-station path a different structural model is adopted which represents the best 1-D approximation of the medium in this azimuth. Thus, lateral inhomogeneities are taken into account in a simplified way. The source is described by the full moment tensor, allowing both deviatoric and volumetric components to be resolved. Although the structural models are simplified for the range of epicentral distances (15〈Δ〈〈170 km) considered, we find that the fit between the synthetic and observed seismograms is satisfactory for frequencies less than a few Hz. The few P-wave polarities available are not sufficient to determine a reliable source mechanism by standard methods, while the waveform inversion allows us to retrieve source mechanisms that are stable with respect to different boundary conditions and in good agreement with the observed polarities. The source time function is the less stable inverted parameter, being the most influenced by the simplification of the structural models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02300765
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  • 7
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    Long range infrasound monitoring of Etna volcano (2019)
    Springer Nature
    Details
    Publication Date: 2019-11-29
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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    PAPER CURRENT
  • 8
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    Complete moment tensor retrieval for weak events: application to orogenic and volcanic areas (1996)
    Elsevier
    Details
    Publication Date: 1996-08-01
    Print ISSN: 0040-1951
    Electronic ISSN: 1879-3266
    Topics: Geosciences , Physics
    Published by Elsevier
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    PAPER CURRENT
  • 9
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    Seismic monitoring of explosions: A method to extract information on the isotropic component of the seismic source (1997)
    Springer
    Details
    Publication Date: 1997-01-01
    Description: The design of a monitoring system for detecting explosions is a very topical problem, both for routine data processing at seismological observatories as well as for the monitoring of a Comprehensive Test Ban Treaty. In this framework it is desirable to have the possibility to quantify the presence of the isotropic component in the seismic source. For this purpose a method is presented, which is based on waveform inversion for the full moment tensor retrieval. The method inverts either full waveforms or separate seismic phases and returns the mechanism and time history of a point source. Moreover, it allows to redefine the hypocentral depth of the event and, in a simplistic way, to optimize the structural model as well. In order to model strong laterally heterogeneous structures, different pairs of structural models can be used for each source-receiver path. The source is decomposed into a volumetric part (V), representing an explosive or implosive component, and into a deviatoric part, containing both the double couple (DC) and the compensated linear vector dipole (CLVD) components. The method is applied to an area in central Switzerland and to the network of the Swiss Seismological Service. The events of interest include both earthquakes and explosions. Despite some modelling inadequacies of the source-time function, the explosions can be well identified with the inverted isotropic component in the source, as long as the number of stations used for the inversion is larger than three. The results of the inversion are better for large epicenter-station distances of the order of 40-90 km.
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
    Published by Springer
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    PAPER CURRENT
  • 10
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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 (1996)
    Oxford University Press
    Details
    Publication Date: 1996-09-01
    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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