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  • 1
    Electronic Resource
    Electronic Resource
    Rupture mechanism and source parameters of Umbria-Marche mainshocks from strong motion data (2000)
    Springer
    Journal of seismology 4 (2000), S. 463-478 
    Details
    ISSN: 1573-157X
    Keywords: directivity ; isochrone ; rupture kinematics ; strong motion data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A long sequence of earthquakes causing few casualties and considerable damage in a wide zone struck Central Italy starting on September 26, 1997. Theearthquakes are characterized by normal faulting mechanism, with a NE-SW(anti-Apenninic direction) tension axis. In this paper we analyze the accelerometric recordings collected by the accelerograph stations belonging to the National Accelerograph Network. About 10 stations were triggered by the mainshocks of the sequence. In particular, a small size foreshock and the two mainshocks that occurred on September,26 (00:33(GMT) MW = 5.7 and 09:40 MW = 6.0) have been recorded by two digital 3-C accelerometers located at near source distances (within 30 km from the faults). These records are relevant to investigate the detail of therupture kinematics, due to the close epicentral distance and azimuthallocation relative to the fault orientation and geometry. Using a trial and error approach we modeled the source mechanism through the fit of the arrival times, the apparent source time duration, the main polarization features and the entire waveforms of the recorded signals, in order to get some insight on the rupture evolution, the location of the fracture origin point and the fault geometry. Based on this fault kinematic model, inferences on fault slip distribution are obtained by modeling the S acceleration waveform, comparing the ray theory synthetics with 1–5 Hz band filtered ground velocity records.The final model shows that the seismic ruptures occurred along two adjacent,sub-parallel, low angle dipping normal faults. Ruptures bothnucleated from the fault bottom and propagated up-dip, showing differentrupture velocity and length. The presence of a transfer zone (barrier)can be suggested by the mainshocks rupture evolution. This transfer zonehas probably controlled the amplitude increase of local stressreleased by the first rupture at its NW edge which triggered about 9 hourslater the second rupture. The inferred model was used to compute the predictedground acceleration in the near source range, using a hybridstatistical-deterministic approach.A similar trial and error method has been also applied to the October 14, 199715:23 earthquake (MW = 5.6). The inferred kinematic model indicates a rupture nucleating from the faultbottom and propagating up-dip, toward the SE direction. Thus the three mainshocks ruptured distinct fault segments, adjacent and slightly offsetfrom one to another.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026523703464
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    Paper (German National Licenses)
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  • 2
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    Quick Determination of the Earthquake Focal Mechanism from the Azimuthal Variation of the Initial P ‐Wave Amplitude (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉When an earthquake occurs, a key parameter in the emergency’s management is the knowledge of the most stressed areas by the ground motion. The focal mechanism is an essential source parameter for producing realistic shake maps. Although the approaches for estimating earthquake location and magnitude are now consolidated, automatic solutions for the focal mechanism are not always provided by the agencies or available at later times after inversion of waveforms for the determination of moment tensor components. We introduce a new approach for the automatic determination of the earthquake focal mechanism, using the spatial distribution of observed absolute initial 〈span〉P〈/span〉‐wave peak amplitudes, corrected for the geometrical attenuation effect, in an evolutionary, Bayesian framework. We applied the proposed methodology to the main earthquakes of the 2016–2017 central Italy seismic sequence finding that our rapid automatic estimates of the focal mechanism are in good agreement with those of the reference solutions.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 3
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    Predicting the Macroseismic Intensity from Early Radiated P-wave Energy for On-site Earthquake Early Warning in Italy (2015)
    Wiley
    Details
    Publication Date: 2015-10-11
    Description: Earthquake Early Warning Systems (EEWS) are potentially effective tools for risk mitigation in active seismic regions. The present study explores the possibility of predicting the macroseismic intensity within EEW timeframes using the squared velocity integral (IV2) measured on the early P-wave signals, a proxy for the P-wave radiated energy of earthquakes. This study shows that IV2 correlates better than the peak displacement measured on P-waves (PD) with both the peak ground velocity and the Housner Intensity, with the latter being recognized by engineers as a reliable proxy for damage assessment. Therefore, using the strong motion recordings of the ITalian ACcelerometric Archive (ITACA 2.0), a novel relationship between the parameter IV2 and the macroseismic intensity (IM) has been derived. The validity of this relationship has been assessed using the strong motion recordings of the INGV Strong Motion Data and ‘ Osservatorio Sismico delle Strutture ’ databases, as well as, in the case of the M W 6 May 29 th 2012 Emilia Earthquake (Italy), comparing the predicted intensities with the ones observed after a macroseismic survey. Our results indicate that P-wave IV2 can become a key parameter for the design of on-site EEWS, capable of proving real-time predictions of the IM at target sites.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Ground-Motion Prediction Equations for South Korea Peninsula (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-10-02
    Description: Ground-motion prediction equations (GMPEs) play a crucial role for estimating the seismic hazard in any region using either a deterministic or a probabilistic approach. Indeed, they represent a reliable and fast tool to predict strong ground motion, given source and propagation parameters. In this article, we estimated GMPEs for the South Korea peninsula. GMPEs were computed for peak ground displacement, peak ground velocity, peak ground acceleration, and spectral accelerations (damping at 5%) at 13 different periods from 0.055 to 5 s. We analyzed data from 222 earthquakes recorded at 132 three-component stations of the South Korea Seismic Network, from 2007 to 2012, with local magnitude ranging between 2.0 and 4.9 and epicentral distances varying from 1.4 to ~600 km. A nonlinear mixed effects technique is used to infer the GMPE coefficients. This technique includes both fixed and random effects and accounts for both inter- and intraevent dependencies in the data. Station-specific corrective coefficients were estimated by a statistical approach and were included in the final ground-motion prediction model. Finally, predictions for peak ground acceleration and spectral acceleration are compared with observations recorded for an M L  5.1 earthquake that occurred in 2014, the data for which were not included in the modeling. Online Material: Figures showing final ground-motion prediction equation models versus observations, and intra- and interevent residuals.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 5
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    Quick Determination of the Earthquake Focal Mechanism from the Azimuthal Variation of the Initial P ‐Wave Amplitude (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉When an earthquake occurs, a key parameter in the emergency’s management is the knowledge of the most stressed areas by the ground motion. The focal mechanism is an essential source parameter for producing realistic shake maps. Although the approaches for estimating earthquake location and magnitude are now consolidated, automatic solutions for the focal mechanism are not always provided by the agencies or available at later times after inversion of waveforms for the determination of moment tensor components. We introduce a new approach for the automatic determination of the earthquake focal mechanism, using the spatial distribution of observed absolute initial 〈span〉P〈/span〉‐wave peak amplitudes, corrected for the geometrical attenuation effect, in an evolutionary, Bayesian framework. We applied the proposed methodology to the main earthquakes of the 2016–2017 central Italy seismic sequence finding that our rapid automatic estimates of the focal mechanism are in good agreement with those of the reference solutions.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 6
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    Kinematic Inversion of Strong-Motion Data Using a Gaussian Parameterization for the Slip: Application to the 2008 Iwate-Miyagi, Japan, Earthquake (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-12-01
    Description: We present a nonlinear technique for the purpose of estimating the distribution of the final slip and the rupture velocity on the fault plane from the inversion of strong-motion records. In this work, the ground-motion simulation is obtained by evaluating the representation integral in the frequency domain, through a finite-element approach, based on a Delaunay’s triangulation of the fault plane. The slip distribution is parameterized by a linear combination of 2D overlapping Gaussian functions. This choice allows us to relate the maximum frequency in the data to the smallest resolvable wavelength on the fault plane, insuring a smooth representation for the slip function. We investigate the capability of such a representation to describe complex slip maps, and we relate the width of the Gaussian function and the overlapping to the minimum wavelength of the slip function. The inverse problem is solved by a two-step procedure aimed at separating the computation of the rupture velocity from the evaluation of the slip distribution. While a global exploration is maintained for the rupture velocity, for each explored value of this quantity, the slip solution is computed as the best solution approaching the observations in the sense of the L2 norm. The nonlinear step is performed through the neighborhood algorithm (NA), while the linear one uses the nonnegative least-squares (NNLS) method. The technique has been applied to retrieve the rupture history of the 2008 Iwate–Miyagi, Japan, earthquake. The slip distribution is characterized by a large slip patch extending from the hypocenter to the southern shallow part of the fault plane, with a maximum amplitude of 6 m. In addition, a relatively smaller asperity is located in the north shallow part of the fault. We found that the rupture lasted about 12 s with an average rupture velocity of about 2.0 km/s. Online Material: Figures showing synthetic inversion test results.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 7
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    Investigating Rupture Direction for Three 2012 Moderate Earthquakes in Northern Italy from Inversion of Peak Ground-Motion Parameters (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-12-01
    Description: We investigate the possibility of inferring the dominant horizontal-rupture direction for moderate earthquakes from the inversion of peak ground-motion parameters. To this aim, we adopt a technique that was devised and applied to large earthquakes for retrieving both the dominant rupture direction and the surface fault projection to be used with a proper distance metric to refine the ShakeMap computation. In the present paper, the procedure was applied to three moderate earthquakes that occurred in 2012 in Northern Italy three days apart: the M  4.2 Pre-Alpi Venete earthquake on 24 January, the M  4.9 Reggio Emilia earthquake on 25 January, and the M  5.4 Parma earthquake on 27 January. For two of the three analyzed events, the technique identifies a dominant horizontal-rupture direction, which is consistent with the strike directions inferred from the focal mechanisms. For the M  5.4 event, which is a deep (about 61 km) thrust-faulting mechanism earthquake, the inferred dominant rupture direction allows identification of the northeast-dipping plane as the fault plane in accordance with the aftershocks distribution.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 8
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    Earthquake source kinematics of moderate earthquakes from the inversion of apparent source time functions (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-05
    Description: We present an approach to infer the slip and rupture velocity distributions on the fault plane from the non-linear inversion of the apparent source time functions, obtained from the empirical Green's function deconvolution method. The main advantage of this technique is that it allows overcoming, in the forward modelling, the limitations related to the computation of the Green's function, as the choice of a correct and reliable earth propagation model. We perform a parameter resolution and uncertainty study, which is based on the analysis of the misfit function in the neighbourhood of the best-fitting model. In this paper, we present the results obtained by applying the technique to synthetic and real records from an M w 4 event which occurred during the 2009 L’Aquila (central Italy) aftershock sequence. Results show a heterogeneous slip distribution, characterized by two main high slip patches located NW of the hypocentre and an average slip of 3.7 cm, corresponding to a seismic model of about 0.82  x 10 15 Nm.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    Ground-motion simulations within ShakeMap methodology: application to the 2008 Iwate-Miyagi Nairiku (Japan) and 1980 Irpinia (Italy) earthquakes (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-12
    Description: ShakeMap package uses empirical ground motion prediction equations (GMPEs) to estimate the ground motion where recorded data are not available. The GMPEs, however, account only for average characteristics of source and wave propagation processes and the ground motion estimate can fail in the near-source area when few stations are available. In this study, we investigate the performance of ShakeMap in the near-fault area when source effects are included at different levels of complexity. We focus on the 2008, M w 7.0, Iwate-Miyagi Nairiku (Japan) earthquake because of the large amount of recording stations which contribute to the definition of a reference shakemap. After shutting off some stations from the original data set, we evaluate the resulting shakemaps bias as if the earthquake was recorded at a smaller number of receivers. We then compute the shakemaps replacing the missing records with synthetic seismograms from a hybrid deterministic-stochastic method for extended fault. We suppose an increasing knowledge of seismic source approximation and of the slip history on the fault, obtained both from the expeditious inversion of teleseismic data and, afterwards, from strong-motion data inversion. In particular, a non-linear kinematic inversion technique allowed us to retrieve a complete kinematic description of the source process on the fault plane. Our results reveal that the integration of real data with synthetics is quite efficient, providing reliable shaking maps mainly when near source recordings are scarce. However, the accuracy of the fault plane position plays a major role in increasing the effectiveness of the results. We then apply the methodology to a poorly instrumented earthquake of similar magnitude, the 1980, M s 6.9, Irpinia (Southern Italy) earthquake. When the peak motions inferred from synthetic seismograms are included in the database, the fit with respect to the observed Mercalli–Cancani–Sieberg intensities improves.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Moment Tensor Resolution: Case Study of the Irpinia Seismic Network, Southern Italy (2014)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2014-06-12
    Description: We present an analysis of the reliability of focal mechanisms obtained through moment tensor inversion at the Irpinia Seismic Network, southern Italy. Our analysis is based on the methods proposed by Zahradník and Custódio (2012) and Sokos and Zahradník (2013) . We present two different studies: (1) we compute maps of theoretical focal mechanism resolution for the Irpinia region and (2) we study the reliability of the solutions obtained from waveform inversion of five regional earthquakes. Theoretically, we find that when data error is the dominant source of error, focal mechanism resolution is better close to the spots of higher station density rather than at the center of the network. Using real data, we were able to successfully study four of the five regional events, in spite of the large source–station distances (up to ~280 km) and significant azimuthal gaps (〉319°). We used variance reduction, double-couple percentage, signal-to-noise ratio, condition number, and focal mechanism variability index to assess the quality of the solutions. Our quality assessment is validated by comparison with independent focal mechanism solutions.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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