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  • 1
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    Toward a New Probabilistic Framework to Score and Merge Ground-Motion Prediction Equations: The Case of the Italian Region (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-04-07
    Description: The ground-motion prediction equation (GMPE) is a basic component for probabilistic seismic-hazard analysis. There is a wide variety of GMPEs that are usually obtained by means of inversion techniques of datasets containing ground motions recorded at different stations. However, to date there is not yet a commonly accepted procedure to select the best GMPE for a specific case; usually, a set of GMPEs is implemented (more or less arbitrarily) in a logic-tree structure, in which each GMPE is weighted by experts, mostly according to gut feeling. Here, we discuss a general probabilistic framework to numerically score and weight GMPEs, highlighting features, limitations, and approximations; finally, we put forward a numerical procedure to score GMPEs, taking into account their forecasting performances, and to merge them through an ensemble modeling. Then, we apply the procedure to the Italian territory; in addition to illustrating how the procedure works, we investigate other relevant aspects (such as the importance of the focal mechanism) of the GMPEs to different site conditions. Online Material: Figures showing regression analysis for peak ground acceleration (PGA) values and location map, and earthquake catalog and summary table of parameters corresponding to each ground-motion prediction equation (GMPE) implemented.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    Monitoring of crustal seismic velocity variations in the L'Aquila fault zone inferred from noise cross-correlation (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-22
    Description: The relative seismic velocity variations possibly associated to large earthquakes can be readily monitored via cross-correlation of seismic noise. In a recently published study, more than 2 yr of continuous seismic records have been analysed from three stations surrounding the epicentre of the 2009 April 6, M w 6.1 L'Aquila earthquake, observing a clear decrease of seismic velocities likely corresponding to the co-seismic shaking. Here, we extend the analysis in space, including seismic stations within a radius of 60 km from the main shock epicentre, and in time, collecting 5 yr of data for the six stations within 40 km of it. Our aim is to investigate how far the crustal damage is visible through this technique, and to detect a potential post-seismic recovery of velocity variations. We find that the co-seismic drop in velocity variations extends up to 40 km from the epicentre, with spatial distribution (maximum around the fault and in the north–east direction from it) in agreement with the horizontal co-seismic displacement detected by global positioning system (GPS). In the first few months after L'Aquila earthquake, the crust's perturbation in terms of velocity variations displays a very unstable behaviour, followed by a slow linear recovery towards pre-earthquake conditions; by almost 4 yr after the event, the co-seismic drop of seismic velocity is not yet fully recovered. The strong oscillations of the velocity changes in the first months after the earthquake prevent to detect the fast exponential recovery seen by GPS data. A test of differently parametrized fitting curves demonstrate that the post-seismic recovery is best explained by a sum of a logarithmic and a linear term, suggesting that processes like viscoelastic relaxation, frictional afterlip and poroelastic rebound may be acting concurrently.
    Keywords: Seismology
    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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  • 3
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    The ShakeMap Atlas for the City of Naples, Italy (2013)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2013-10-25
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 4
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    Toward a New Probabilistic Framework to Score and Merge Ground-Motion Prediction Equations: The Case of the Italian Region [Article] (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-04-15
    Description: The ground-motion prediction equation (GMPE) is a basic component for probabilistic seismic-hazard analysis. There is a wide variety of GMPEs that are usually obtained by means of inversion techniques of datasets containing ground motions recorded at different stations. However, to date there is not yet a commonly accepted procedure to select the best GMPE for a specific case; usually, a set of GMPEs is implemented (more or less arbitrarily) in a logic-tree structure, in which each GMPE is weighted by experts, mostly according to gut feeling. Here, we discuss a general probabilistic framework to numerically score and weight GMPEs, highlighting features, limitations, and approximations; finally, we put forward a numerical procedure to score GMPEs, taking into account their forecasting performances, and to merge them through an ensemble modeling. Then, we apply the procedure to the Italian territory; in addition to illustrating how the procedure works, we investigate other relevant aspects (such as the importance of the focal mechanism) of the GMPEs to different site conditions. Online Material: Figures showing regression analysis for peak ground acceleration (PGA) values and location map, and earthquake catalog and summary table of parameters corresponding to each ground-motion prediction equation (GMPE) implemented.
    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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    The Central Italy Seismic Sequence between August and December 2016: Analysis of Strong-Motion Observations (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-08-26
    Description: Since August 2016, central Italy has been struck by one of the most important seismic sequences ever recorded in the country. In this study, a strong-motion data set, consisting of nearly 10,000 waveforms, has been analyzed to gather insights about the main features of ground motion, in terms of regional variability, shaking intensity, and near-source effects. In particular, the shake maps from the three main events in the sequence have been calculated to evaluate the distribution of shaking at a regional scale, and a residual analysis has been performed, aimed at interpreting the strong-motion parameters as functions of source distance, azimuth, and local site conditions. Particular attention has been dedicated to near-source effects (i.e., hanging wall/footwall, forward-directivity, or fling-step effects). Finally, ground-motion intensities in the near-source area have been discussed with respect to the values used for structural design. In general, the areas of maximum shaking appear to reflect, primarily, rupture complexity on the finite faults. Large ground-motion variability is observed along the Apennine direction (northwest–southeast) that can be attributed to source-directivity effects, especially evident in the case of small-magnitude aftershocks. Amplifications are observed in correspondence to intramountain basins, fluvial valleys, and the loose deposits along the Adriatic coast. Near-source ground motions exhibit hanging-wall effects, forward-directivity pulses, and permanent displacement.
    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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    Accounting for source effects in the ShakeMap procedure: the 2000 Tottori and the 2008 Miyagi earthquakes (2013)
    Oxford University Press
    Details
    Publication Date: 2013-08-13
    Description: Real-time seismology has made significant improvements in recent years, with source parameters now available within a few tens of minutes after an earthquake. It is likely that this time will be further reduced, in the near future, by means of increased efficiency in real-time transmission, increasing data coverage and improvement of the methodologies. In this context, together with the development of new ground motion predictive equations (GMPEs) that are able to account for source complexity, the generation of strong ground motion shaking maps in quasi-real time has become ever more feasible after the occurrence of a damaging earthquake. However, GMPEs may not reproduce reliably the ground motion in the near-source region where the finite fault parameters have a strong influence on the shaking. In this paper we test whether accounting for source-related effects is effective in better characterizing the ground motion. We introduce a modification of the GMPEs within the ShakeMap software package, and subsequently test the accuracy of the newly generated shakemaps in predicting the ground motion. The test is conducted by controlling the performance of ShakeMap as we decrease the amount of the available information. We then update ShakeMap with the GMPE modified with a corrective factor accounting for source effects, in order to better constrain these effects that likely influence the level of (near-source) ground shaking. We investigate two well-recorded earthquakes from Japan (the 2000 Tottori, M w 6.6, and the 2008 Iwate-Miyagi, M w 7.0, events) where the instrumental coverage is as dense as needed to ensure an objective appraisal of the results. The results demonstrate that the corrected GMPE can capture only some aspects of the ground shaking in the near-source area, neglecting other multidimensional effects, such as propagation effects and local site amplification.
    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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  • 7
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    Spatio-temporal seismic velocity variations associated to the 2016-2017 central Italy seismic sequence from noise cross-correlation (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Summary〈/div〉We investigate the temporal changes of crustal velocity associated to the seismic sequence of 2016-2017, which struck central Italy with a series of moderate to large earthquakes. We cross-correlate continuous recordings of two years of ambient seismic noise from a network of 28 stations within a radius of 90 km around Amatrice town. We then map the spatio-temporal evolution of the velocity perturbations under the effect of subsequent earthquakes. Coinciding with each of the three mainshocks of the sequence we observe a sudden drop of seismic velocity which tends to quickly recover in the short term. After the end of the strongest activity of the sequence, the coseismic velocity changes display gradual healing towards pre-earthquake conditions following a quasi-linear trend, such that by the end of 2017 about 75 per cent of the perturbation is recovered. The spatial distribution of the velocity drop fluctuates with time, and the area that shows the most intense variations beyond the ruptured fault system elongates in the NE direction. This zone roughly corresponds to a region of foredeep sedimentary deposits consisting of highly hydrated and porous sandstones, which respond to the passage of seismic waves with increased pore pressure and crack number, leading to a reduction of the effective relative velocity.〈/span〉
    Print ISSN: 2051-1965
    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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  • 8
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    The New ShakeMap in Italy: Progress and Advances in the Last 10 Yr (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉This work describes a procedure to configure U.S. Geological Survey (USGS)‐ShakeMap for a given region. The procedure is applied to Italy to update and improve the ShakeMap service provided by Istituto Nazionale di Geofisica e Vulcanologia (INGV). The new configuration features (1) the adoption of recently developed ground‐motion models (GMMs) and of an updated map of VS30 for the local site effects and (2) the adoption of the newly developed USGS‐ShakeMap version 4 (v.4) software (see 〈a href="https://pubs.geoscienceworld.org/srl#sc10Data%20and%20Resources"〉Data and Resources〈/a〉). We have used the same subdivision in tectonic regimes adopted for the GMMs for the new Italian seismic hazard model (MPS19, 〈a href="https://pubs.geoscienceworld.org/srl#rf35"〉Meletti 〈span〉et al.〈/span〉, 2017〈/a〉) and selected the most appropriate GMMs after application of a ranking procedure consisting of statistical tests. A cross‐validation technique has been applied to test the goodness of the selected configuration and to compare the ShakeMaps obtained with the old (〈a href="https://pubs.geoscienceworld.org/srl#rf36"〉Michelini 〈span〉et al.〈/span〉, 2008〈/a〉) and the new settings. Finally, the INGV ShakeMap workflow has been renovated to exploit the data and analysis chain implemented at INGV from real‐time data streams acquisition to analyst revised waveforms including additional data (e.g., revised location, fault geometry) that may become available days after the event occurrence.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 9
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    The New ShakeMap in Italy: Progress and Advances in the Last 10 Yr (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉This work describes a procedure to configure U.S. Geological Survey (USGS)‐ShakeMap for a given region. The procedure is applied to Italy to update and improve the ShakeMap service provided by Istituto Nazionale di Geofisica e Vulcanologia (INGV). The new configuration features (1) the adoption of recently developed ground‐motion models (GMMs) and of an updated map of VS30 for the local site effects and (2) the adoption of the newly developed USGS‐ShakeMap version 4 (v.4) software (see 〈a href="https://pubs.geoscienceworld.org/srl#sc10Data%20and%20Resources"〉Data and Resources〈/a〉). We have used the same subdivision in tectonic regimes adopted for the GMMs for the new Italian seismic hazard model (MPS19, 〈a href="https://pubs.geoscienceworld.org/srl#rf35"〉Meletti 〈span〉et al.〈/span〉, 2017〈/a〉) and selected the most appropriate GMMs after application of a ranking procedure consisting of statistical tests. A cross‐validation technique has been applied to test the goodness of the selected configuration and to compare the ShakeMaps obtained with the old (〈a href="https://pubs.geoscienceworld.org/srl#rf36"〉Michelini 〈span〉et al.〈/span〉, 2008〈/a〉) and the new settings. Finally, the INGV ShakeMap workflow has been renovated to exploit the data and analysis chain implemented at INGV from real‐time data streams acquisition to analyst revised waveforms including additional data (e.g., revised location, fault geometry) that may become available days after the event occurrence.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 10
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    The ShakeMap Atlas for the City of Naples, Italy (2013)
    Seismological Society of America
    Details
    Publication Date: 2013-10-24
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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