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  • 1
    Electronic Resource
    Electronic Resource
    Local source tomography: applications to Italian areas (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 2 (1990), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We describe three study cases in which we used local earthquake and shot travel-time residuals to investigate the upper crustal structure of three regions in Italy. We inverted for velocity and hypocentral parameters using a damped least-squares technique making use of parameter (velocity and hypocentre) separation. The three studied regions are in Italy, namely (a) the Vulsinian Volcanic Complex (Latium), where there is an active geothermal field; (b) the Irpinia (Campania–Lucania) region, in the Southern Appennines, site of the strongest earthquake in Italy for at least 65 years (November 1980, Ms= 6.9); (c) the Friuli region, in Northeastern Italy, where another strong earthquake (Ms= 6.5) occurred in 1976. The computed shallow velocity models generally correspond with surface geological structures. For the three studied areas, the main results are, respectively: (a) A low-velocity anomaly detected in the centre of the Vulsinian Volcanic Complex at a depth of 5–8 km, probably due to anomalous heat flow caused by a partially molten or cooling intrusive body; (b) the identification of a deep (10 km) discontinuity in the crust beneath the Irpinia fault zone, approximately corresponding with the fault extension at depth; (c) the detection of a wedge of high-velocity, high density material at seismogenic depth (5–10 km) beneath the Friuli region, interpreted as a buried thrust of the metamorphic basement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1990.tb00125.x
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    Paper (German National Licenses)
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  • 2
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    Regional Moment Tensors of the 2009 L'Aquila Earthquake Sequence (2011)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2011-06-01
    Description: Broadband waveform inversion of ground velocities in the 0.02-0.10 Hz frequency band is successfully applied to 181 earthquakes with ML[≥]3 of the April 2009 L'Aquila, Italy, earthquake sequence. This was made possible by the development of a new regional crustal velocity model constrained by deep crustal profiles, surface-wave dispersion and teleseismic P-wave receiver functions, and tested through waveform fit. Although all earthquakes exhibit normal faulting, with the fault plane dipping southwest at about 55{degrees} for the majority of events, a subset of events had much shallower dips. The issue of confidence in the derived parameters was investigated by applying the same inversion procedure by two groups who subjectively selected different traces for inversion. The unexpected difficulty in modeling the regional broadband waveforms of the mainshock as a point source was investigated through an extensive finite-fault modeling of broadband velocity and accelerometer data, which placed the location of major moment release up-dip and about 4-7 s after the initial first-arrival hypocentral parameters.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 3
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    Coda-derived source spectra, moment magnitudes and energy-moment scaling in the western Alps (2020)
    Ras
    Details
    Publication Date: 2020-10-16
    Description: A stable estimate of the earthquake source spectra in the western Alps is obtained using an empirical method based on coda envelope amplitude measurements described by Mayeda for events ranging between MW∼ 1.0 and ∼5.0. Path corrections for consecutive narrow frequency bands ranging between 0.3 and 25.0 Hz were included using a simple 1-D model for five three-component stations of the Regional Seismic network of Northwestern Italy (RSNI). The 1-D assumption performs well, even though the region is characterized by a complex structural setting involving strong lateral variations in the Moho depth. For frequencies less than 1.0 Hz, we tied our dimensionless, distance-corrected coda amplitudes to an absolute scale in units of dyne cm by using independent moment magnitudes from long-period waveform modelling for three moderate magnitude events in the region. For the higher frequencies, we used small events as empirical Green's functions, with corner frequencies above 25.0 Hz. For each station, the procedure yields frequency-dependent corrections that account for site effects, including those related to fmax, as well as to S-to-coda transfer function effects. After the calibration was completed, the corrections were applied to the entire data set composed of 957 events. Our findings using the coda-derived source spectra are summarized as follows: (i) we derived stable estimates of seismic moment, M0, (and hence MW) as well as radiated S-wave energy, (ES), from waveforms recorded by as few as one station, for events that were too small to be waveform modelled (i.e. events less than MW∼ 3.5); (ii) the source spectra were used to derive an equivalent local magnitude, ML(coda), that is in excellent agreement with the network averaged values using direct S waves; (iii) scaled energy, graphic, where ER, the radiated seismic energy, is comparable to results from other tectonically active regions (e.g. western USA, Japan) and supports the idea that there is a fundamental difference in rupture dynamics between small and large crustal earthquakes in tectonically active regions.
    Description: Published
    Description: 263–275
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Intrinsic and scattering seismic wave attenuation in the Central Apennines (Italy) (2021)
    Elsevier
    Details
    Publication Date: 2021-01-04
    Description: Recently, an earthquake sequence formed by a series of subsequences characterized by large earthquakes (three events M ≥ 6.0 and five events M ≥ 5.0) occurred in the Central Apennines in 6–7 months during 2016–2017. Several studies interpreted this cascading type of earthquake occurrence as associated with fluid movements through an interconnected network of cracks around the active faults that triggered the subsequences in different time and location. In the present study we aim to verify if the presence of fluids is confirmed by the pattern of seismic wave attenuation. To do so we separately estimate the space-averaged parameters intrinsic Qi−1 and scattering Qs−1, proportional to the correspondent attenuation parameters, by applying a modified Multiple Lapse Time Window Analysis (MLTWA), in order to establish reference background values for the study region. MLTWA measures the decay of S-wave energy with distance and lapse time and fit it to the Energy Transport Equation solution for scattering, yielding the seismic albedo, B0 = Qs−1/Qt−1 and the extinction Length, Le,∝Qt−1 parameters as a function of frequency. The knowledge of the separated attenuation parameters allows determining which process of seismic energy dissipation dominates in the region. In the present study B0 results to be around0.6 (at 1.5 Hz) and decreases with increasing frequency down to 0.2 indicating that the attenuation of the seismic energy carried by S-wave is controlled by intrinsic dissipation rather than by scattering. Moreover, the intrinsic attenuation is frequency dependent (f −0.9 for the uniform model and f −0.4 for the crust/Moho model). This behavior well matches with the presence of fluids in the faults and fracture zones in the central Apennines, in agreement with results from other independent studies in the region. Finally, a comparison among the attenuation parameters estimated for this area and those measured in several areas of Italy and other parts of the world is presented together with a discussion on the comparison between the present MLTWA attenuation estimates and homologous results obtained for the same area with different approaches.
    Description: Published
    Description: 106498
    Description: 7T. Variazioni delle caratteristiche crostali e precursori sismici
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Ground-Motion characterization and modeling of the 2016 Central Italy earthquake sequence (2020)
    Details
    Publication Date: 2020-10-16
    Description: Central Apennines is one of the most seismically active areas in Italy, where a long history of earthquake (69 events with magnitude 5.0 or greater, and 7 with magnitude exceeding 6.0) has strongly influenced the development of earthquake-resistant structural design. The Amatrice earthquake with a magnitude of 6.0 has occurred on August 24th, 2016 at 1:36:32 UTC and heavily damaged the villages of Amatrice and Accumoli. In following five months nine seismic events with magnitude M〉5.0 occurred in the area. The largest event of the sequence (M6.5) occurred on October 30th at 06:40:18 UTC with the epicenter located in the vicinity of the town of Norcia. The sequence in progress together with that of L'Aquila (6 April 2009) provides a massive set of seismological data (3 events with magnitude 6.0, up to a maximum magnitude 6.5. The main objective of this study is to provide the quantification of the ground motion induced by a given earthquake that may have effects on the territory. Therefore, we obtain the scaling relationships for the high frequency ground motion in the region and regressions were carried out over 91,000 selected waveforms recorded during 672 events with magnitude ranging from Mw3.0 to Mw 6.5. For sequence we both use accelerometric and seismometric data recorded by the seismic stations of the National Accelerometric Network (RAN) and the National INGV Seismic Network (RSN). Regional attenuation and source scaling are parameterized to describe the observed ground motions as function of distance, frequency and magnitude. Peak ground velocities are measured in the selected narrow frequency bands from 0.25 to 20.0 Hz; observed peaks are regressed to define a regional attenuation function, a set of excitation terms and a set of site response terms. Results are then modeled through the random vibration theory. Finally, these set of parameters (frequency dependent attenuation, source and site related spectral parameters) are performed in order to predict the earthquake-induced ground motion in the region and then validated against recordings. We also compare our predicted ground motion parameters with recent global and regional ground motion prediction equations and reveal the importance of the retrieving specific regional seismic parameters for the ground motion predictive equations.
    Description: Unpublished
    Description: Washington - USA
    Description: 4T. Sismicità dell'Italia
    Keywords: ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 6
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    Assessing the nature of stochastic uncertainties for ground motion predictions: the Apennines, Italy. (2020)
    Details
    Publication Date: 2020-10-16
    Description: In this study we aim to assessing the nature of stochastic uncertainties in ground-motion predictions, by including the variability of region-specific crustal attenuation in time and space in the Central/Northern Apennines (Italy), using the events occurred during 2016-2017 earthquake sequence. Spectral characteristics of excitation, attenuation and duration of ground motion are derived through a regression analysis of the peak ground velocities in the frequency range of 0.25–22 Hz. Regressions are carried out over thousands time windows before and after the Amatrice (M6.0), Visso (M5.9) and Norcia (M6.3) earthquakes, in order to evaluate the fluctuations in seismic wave attenuation induced by the largest mainshocks of the seismic sequence. Propagation terms are modeled using random vibration theory, through a grid search over the attenuation parameters. Here we show that crustal attenuation is strongly affected by transients triggered by the main events, and quantify the impact of the seismic wave attenuation variability on the ground-motion hazard in the Central/Northern Apennines. We also determine the effect of spatial variability of crustal attenuation and its contribution to stochastic uncertainties in ground motion predictions.
    Description: Unpublished
    Description: Vienna - Austria
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Keywords: ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 7
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    On the Heterogeneity of the Earthquake rupture (2021)
    Oxford University Press
    Details
    Publication Date: 2021-04-14
    Description: The scaling of earthquake parameters with seismic moment and its interpretation in terms of self- similarity is still debated in the literature. We address this question by examining a worldwide compilation of corner frequency-based and elastic rebound theory (ERT)-based fault slip, area and stress drop values for earthquakes ranging in magnitude from -0.7 to 7.8. We find that corner frequency estimates of slip (and stress drop) scale differently than those inferred from the ERT approach, where the latter deviates from the generally accepted constant stress drop behavior of so- called self-similar scaling models. We also find that average slips from finite-source models are consistent with corner frequency scaling, whereas peak slip values are more consistent with the ERT scaling. The different scaling of corner frequency- and ERT-based estimates of slip and stress drop with earthquake size is interpreted in terms of heterogeneity of the rupture process. ERT-based estimates of stress drop decrease with seismic moment suggesting a self-affine behavior. Despite the inferred heterogeneity at all scales, we do not observe a clear effect on the Brune stress drop scaling with earthquake size.
    Description: Published
    Description: 1771–1781
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: Earthquake dynamics ; Earthquake source observations ; Dynamics and mechanics of faulting ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Forecasting the Next Parkfield Mainshock on the San Andreas Fault (California) (2021)
    Medwin P.
    Details
    Publication Date: 2021-05-12
    Description: A physical model was recently proposed to describe the phenomenon of coupling erosion that took place in the Japan Trough between 1998 and 2009, and the subsequent dynamic rupture occurred during the 2011 M9.1 Tohoku-Oki earthquake. Although 75% of the coupled area of the Japanese subduction was eroded away before nucleation, coseismic slip displaced both the locked (velocity weakening) and the eroded (velocity-strengthening) parts of the asperity. Here we show that a similar phenomenon of erosion repeatedly takes place at Parkfield on a NW patch of the SAF close to the asperity responsible for the repeating M6 earthquakes. We consider the variance of the spatial center of daily seismic activity along the SAF fault calculated on a moving time window. Initially the variance linearly grows due to increasing frictional engagement up to a maximum value. Then a process of erosion of the coupled area of the fault linearly reduces the variance until the stress is transferred onto the adjacent asperity, leading to failure. When halted due to a stress perturbation from the 1983 Coalinga earthquake, the process promptly resumes a virtually unchanged increasing trend. The stable and regular decrease of the variance started in early 1988 allows a very accurate retrospective prediction of the time of occurrence of the 2004 main shock. The process is repeating itself during the current seismic cycle, which, if undisturbed, will produce another mainshock in mid-2024.
    Description: Published
    Description: 7T. Variazioni delle caratteristiche crostali e precursori sismici
    Description: N/A or not JCR
    Keywords: Forecasting the next M6 Parkfield earthquake
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Modulation of seismic attenuation at Parkfield, before and after the 2004 M6 earthquake, and one example from the Geysers geothermal field. (2020)
    Details
    Publication Date: 2020-12-22
    Description: Seismic attenuation is generally thought to be a constant, or a simple monotonic function of frequency, and generally not a function of time. Examples of exceptions include attenuation enhancement due to shallow earthquake-induced damage, and fluctuations due to fluid diffusion. In reality, seismic attenuation fluctuates continuously in time at all frequencies, and the presence of cracks, their density and connectivity, as well as the presence and saturation of fluids, play a central role in defining such behavior. Due to multiple mechanisms, the crack density within a fault’s damage zone varies throughout the seismic cycle. Moreover, non-tectonic stress loads, seasonal or tidal, can change the crack density of crustal rocks, and leave detectable signatures on seismic attenuation. A strong signature can also be left on the crustal attenuation by a stress transfer from a nearby fault. Here we show that attenuation time histories from the San Andreas Fault (SAF) at Parkfield are affected by seasonal loading cycles, as well as by 1.5–3 year periodic variations of creep rates, consistent with published results that documented a broad spectral peak, between 1.5 and 4 years, of the spectra calculated over the activity of repeating earthquakes, and over InSAR time series. After the Parkfield mainshock, the modulation of seismic attenuation is clearly correlated to tidal forces. Opposite attenuation trends are seen on the two sides of the fault up to the M6.5 2003 San Simeon earthquake, when attenuation changed discontinuously, in the same directions of the relative trends. Attenuation increased steadily for over one year on the SW side of the SAF, until the San Simeon earthquake, whereas it decreased steadily on the NE side of the SAF, roughly for the 6 months prior to the event. Random fluctuations are observed up to the 2004 M6 Parkfield mainshock, when rebounds in opposite directions are observed, in which attenuation decreased on the SW side, and increased on the NE side. Another example of changes of attenuation with time is given for the Geysers geothermal field, where a large data set of earthquake recordings from a dense temporal deployment are analyzed and results are given in terms of 1/Q(f,t).
    Description: Published
    Description: San Francisco - USA
    Description: 3T. Sorgente sismica
    Keywords: seismic attenuation
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Oral presentation
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  • 10
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    On the relationship between ML and MW in a broad range: an example from the Apennines, Italy (2018)
    Details
    Publication Date: 2021-05-12
    Description: Being tied to a physical quantity, moment magnitude (Mw) should be the reference estimate of earthquake size and used whenever possible. Local magnitude (ML) represents a simple alternative for a reliable estimate of size, its best use being either for quick outcomes or when the computation of Mw is difficult (e.g., for small earthquakes). However, ML and Mw are profoundly different and not interchangeable. Here, we analyze a large set of 1509 ML–Mw data points from earthquakes of the central and northern Apennines (CNA), quantify the empirical scaling, and look for features of global validity. Our data set is made of 449 unpublishedMws from moment tensor solutions of events from the Amatrice-Visso-Norcia (AVN) sequence, 170 published Mws from moment tensor solutions of events from the L’Aquila seismic sequence (2009), and 890 published ML–Mw data points from earthquakes of the Altotiberina fault (ATF, 2010–2014; Mws from spectral correction). We integrate our empirical data set by computing the local magnitudes of the events from the AVN and L’Aquila sequences. Our analysis of CNA earthquakes shows that, for earthquakes up to a crossover magnitude MLco ≈ 4:3: Mw = 2/3 ML + C′; C′ = 1.14. Moreover, for earthquakes with ML 〉 MLco, up to ML 6.5, our data suggest Mw = bML + C′′; b = 1.28; C′′= −1:50, in which b depends on the combined effects of source scaling and crustal attenuation, and C′ and C″ on regional attenuation (G (r) , Q (f) , κ0), focal depth, and rigidity at source. Finally, a synthetic study calibrated on the crustal attenuation and the source characteristics of the AVN data set reproduces the observed scaling between ML and Mw, predicting that MLs in the analyzed region saturate above ML ∼ 6:5. Smooth transitions are predicted between the different regimes.
    Description: Published
    Description: 1018-1024
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Keywords: magnitude
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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