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  • 1
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2017-04-04
    Description: We performed a regional study of earthquake ground motion scaling relations to provide the seismic hazard community of Israel with a new attenuation relationship that could be used for the prediction of earthquake-induced ground motion. Strong earthquakes are rather scarce in Israel and the existing collection of records from strong earthquakes is not sufficient to allowthe use of traditional regression methods to develop a regional attenuation relationship. We used velocity seismograms from the Israel Seismic Network to estimate the distance and frequency dependence of ground motion in the Israel region from frequent, smaller regional earthquakes. Our analyses included 4814 waveforms recorded by 30 stations of the Israel Seismic Network from 2000 to 2005. We restricted our analysis to 330 events recorded at five or more stations, with duration magnitudes ranging between 1.0 and 5.2. We derived empirical excitation, site and regional attenuation terms by regressing the peak amplitudes of narrowband-filtered seismograms around the shear wave arrivals and the rms Fourier spectral amplitudes taken around the specific sampling frequency. In order to optimize the attenuation parameters in our scaling model, we used a simple grid search. An optimal solution for minimal error between empirical and theoretical attenuation function was found for the quality parameter Q( f ) = 298 f^0.67 and the geometrical spreading g(r ) parametrized as a bilinear, piecewise function: r^−0.74 for r ≤ 60 km and r^−0.47 for r 〉 60 km. The spectral parameters κ of 0.015 s and stress drop increasing from 0.3 to 4 MPa were used to model the excitation spectra. A theoretical modelling effort based on Brune’s source spectrum and Random Vibration Theory (RVT) was performed on the attenuation and source parameters estimated in this study. Comparison of the attenuation relationship derived with locally measured ground motions shows excellent agreement with the data in the magnitude range forwhichwe have observations and seems to be adequate for predictions of earthquake ground motion for the Israel region. Comparison of Peak Ground Acceleration (PGA) predictions, based on our scaling relationship with those that have been recently used for seismic hazard analysis in Israel shows that our attenuation relationship predicts significantly lower ground motions than other relations.
    Description: Published
    Description: 1127 - 1140
    Description: 4.2. TTC - Scenari e mappe di pericolosità sismica
    Description: JCR Journal
    Description: reserved
    Keywords: weak-motion ; strong-motion ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2017-04-04
    Description: We produce probabilistic seismic hazard assessments for the Central Apennines, Italy, using time-dependent models that are characterized using a Brownian Passage Time (BPT) recurrence model. Using aperiodicity parameters,  of 0.3, 0.5, and 0.7, we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters. For the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults. We use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault (floating fault model) to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation. We show maps for peak ground acceleration (PGA) and 1.0-Hz spectral acceleration (SA1) on rock having 10% probability of exceedence (PE) in 50 years. We produce maps to compare the separate contributions of smoothed seismicity and fault components. In addition we construct maps that show sensitivity of the hazard for different  parameters and the Poisson model. For the Poisson model, the addition of fault sources to the smoothed seismicity raises the hazard by 50 % at locations where the smoothed seismicity contributes the highest hazard, and up to 100 % at locations where the hazard from smoothed seismicity is low. For the strongest aperiodicity parameter (smallest ), the hazard may further increase 60-80 % or more or may decrease by as much as 20 %, depending on the recency of the last event on the fault that dominates the hazard at a given site. In order to present the most likely earthquake magnitude and/or the most likely source-site distance for scenario studies, we deaggregate the seismic hazard for SA1 and PGA for two important cities (Roma and l’Aquila) . For PGA, both locations show the predominance of local sources, having magnitudes of about 5.3 and 6.5 respectively. For SA1 at a site in Rome, there is significant contribution from local smoothed seismicity, and an additional contribution from the more distant Apennine faults having magnitude around 6.8. For l’Aquila, the predominant sources remain local. In order to show the variety of impact of different  values we also obtained deaggregations for another three sites. In general, as  decreases (periodicity increases), the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates. This effect is strongest for the long-period (1 s) ground motions.
    Description: In press
    Description: 4.2. TTC - Scenari e mappe di pericolosità sismica
    Description: JCR Journal
    Description: open
    Keywords: Time dependent ; Deaggregations ; Central Apennines, Italy ; Uncertainties ; Aperiodicity ; PSHA ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
    Publication Date: 2017-04-04
    Description: The amount of energy radiated from an earthquake can be measured using recent methods based on earthquake coda signals and spectral ratios. Such methods are not altered by either site or directivity effects, with the advantage of a greatly improved accuracy. Several studies of earthquake sequences based on the above measurements showed evidence of a breakdown in self-similarity in the moment to energy relation. Radiated energy can be also used as a gauge to estimate the average dynamic stress drop on the fault. Here we compute the dynamic stress drop, infer the co-seismic friction and estimate the co-seismic heating resulting from the frictional work during events from different main shock-aftershock earthquake sequences. We relate the dynamic friction to the maximum temperature rise estimated on the faults for each earthquake. Our results are strongly indicative that a thermally triggered dynamic frictional weakening is present, responsible for the breakdown in self-similarity. These observations from seismic data are compatible with recent laboratory evidence of thermal weakening in rock friction under seismic slip-rates, associated to various physical processes such as melting, decarbonation or dehydration.
    Description: Kevin Mayeda was supported under Weston Geophysical subcontract No. GC19762NGD and AFRL contract No. FA8718-06-C-0024. Work by L. Malagnini was performed under the auspices of the Dipartimento della Protezione Civile, under contract S3 – INGV-DPC (2007-2009), project: “Valutazione rapida dei parametri e degli effetti dei forti terremoti in Italia e nel Mediterraneo”.
    Description: Published
    Description: B06319
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: earthquake radiation ; coda ; friction ; self-similarity ; dynamic weakening ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Federazione Italiana di Scienze della Terra
    Publication Date: 2017-04-04
    Description: Il terremoto di Haiti del 12 gennaio 2010 (Mw 7.0) si è verificato alle ore 16:53:09 locali (21:53:09 UTC). L’epicentro è stato localizzato a circa 25 chilometri da Port-au-Prince, la capitale, con una profondità ipocentrale di 13 km (fonte United States Geological Survey, USGS). USGS ha localizzato sei repliche nelle due ore successive al terremoto principale, di magnitudo compresa tra 4.5 e 5.9. (5.9, 5.5, 5.1, 4.8, 4.5, e 4.5). Nelle prime nove ore successive all’evento principale, sono state registrate 26 repliche di magnitudo M ≥ 4.2, dodici delle quali di magnitudo M ≥ 5.0.
    Description: Published
    Description: 42-46
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: N/A or not JCR
    Description: open
    Keywords: HAITI ; TERREMOTO 12 GENNIO ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
    Publication Date: 2017-04-04
    Description: The Abruzzo earthquake on April 6 this year was surprising for several reasons. Although the historical record shows that the city of L’Aquila has suffered intensity IX or higher several times, this earthquake caused stronger shaking than any other in the area for the past 300 years. In addition, the mechanism displays clear extensional stresses in a region characterized by shortening during the Miocene and the mainshock was heralded by a foreshock swarm.
    Description: Published
    Description: 1
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: N/A or not JCR
    Description: open
    Keywords: ABRUZZO ; L'AQUILA EARTHQUAKE ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
    Publication Date: 2017-04-04
    Description: This study documents another unique property of local and regional shear!wave coda: that scattering in the Earth’s crust averages out source heterogeneities such as focal mechanism and directivity. We consider two recent events which exhibited significant source directivity. The first, an Mw 4.2 Oakland hills, California strike!slip event on July 20, 2007, resulted in uncharacteristically large amounts of damage in the Montclair and south Berkeley neighborhoods, along strike and north!west of the hypocenter, but almost no damage to the south!east. The second event, the Mw 5.9 Wells, Nevada dip!slip event of February 21, 2008, was well!recorded by the Earthscope Transportable Array (USArray) and determined to exhibit south!west directivity. We conclude with an example of corner!frequency ( fc) estimates from the Wells sequence, which showcase the coda’s low variance, and find that scaling is non!self!similar, suggesting a change in dynamics between the mainshock and aftershocks.
    Description: Published
    Description: L07306
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: reserved
    Keywords: Source Scaling ; Radiated Energy ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
    Publication Date: 2017-04-04
    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, surfacewave dispersion and teleseismic Pwave receiver functions and tested through waveform fit. Although all earthquakes exhibit normal faulting, with the fault plane dipping southwest at about 55º 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 finitefault modeling of broadband velocity and accelerometer data, which placed the location of major moment release updip and about 47 seconds after the initial firstarrival hypocentral parameters.
    Description: Published
    Description: 975-993
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: L'Aquila sequence ; focal mechanisms ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
    Publication Date: 2017-04-04
    Description: We estimate seismological fracture energies from two subsets of events selected from the seismic sequences of L’Aquila (2009), and Northridge (1994): 57 and 16 selected events, respectively, including the main shocks. Following ABERCROMBIE and RICE (2005), we postulate that fracture energy (G) represents the post-failure integral of the dynamic weakening curve, which is described by the evolution of shear traction as a function of slip. Following a direct-wave approach, we compute mainshock-/aftershock-source spectral ratios, and analyze them using the approach proposed by MALAGNINI et al. (this issue, 2014) to infer corner frequencies and seismic moment. Our estimates of source parameters (including fracture energies) are based on best-fit grid searches performed over empirical source spectral ratios. We quantify the source scaling of spectra from small and large earthquakes by using the MDAC formulation of WALTER and TAYLOR (2001). The source parameters presented in this paper must be considered as point source estimates representing averages calculated over specific ruptured portions of the fault area. In order to constrain the scaling of fracture energy with coseismic slip, we investigate two different slip-weakening functions to model the shear traction as a function of slip: (i) a power law, as suggested by ABERCROMBIE and RICE (2005), and (ii) an exponential decay. Our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies, both for the main events and for their aftershocks, regardless of the significant differences in the energy budgets between the large (main) and small earthquakes (aftershocks). Using the power-law slip-weakening function would lead us to a very different situation: in our two investigated sequences, if the aftershock scaling is extrapolated to events with large slips, a power law (a la Abercrombie and Rice) would predict unrealistically large stress drops for large, main earthquakes. We conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values, while still describing the abrupt shear-stress degradation observed in high-velocity laboratory experiments (e.g., DI TORO et al., 2011).
    Description: Published
    Description: 2709-2730
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: Fault friction, Dynamic fault lubrication, earthquake source scaling ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
    Publication Date: 2017-04-04
    Description: We provide a complete description of the characteristics of excitation and attenuation of the ground motion in the Lake Van region (eastern Turkey) using a data set that includes three-component seismograms from the 23 October 2011 Mw 7.1 Van earthquake, as well as its aftershocks. Regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance, frequency, and magnitude. Peak ground velocities are measured in selected narrow frequency bands from 0.25 to 12.5 Hz; observed peaks are regressed to define a piecewise linear regional attenu- ation function, a set of excitation terms, and a set of site response terms. Results are modeled through random vibration theory (see Cartwright and Longuet-Higgins, 1956). In the log–log space, the regional crustal attenuation is modeled with a bilinear geo- metrical spreading g r characterized by a crossover distance at 40 km: g r ∝ r^−1 fits our results at short distances (r 〈 40 km), whereas g r ∝ r^−0.3 is better at larger distances (40 〈 r 〈 200 km). A frequency-dependent quality factor, Q f =100( f/fref)^ 0:43 (in which fref 1.0 Hz), is coupled to the geometrical spreading. Because of the inherent trade-off of the excitation/attenuation parameters (Δσ and κ), their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes. After choosing a Brune stress drop ΔσBrune 4 MPa at Mw 3:5, we were able to define (1) an effective high frequency, distance- and mag- nitude-independent roll-off spectral parameter, κeff = 0:03 s and (2) a size-dependent stress-drop parameter, which increases with moment magnitude, from ΔσBrune 4 MPa at Mw 3.5 to ΔσBrune 20 MPa at Mw 7.1. The set of parameters mentioned here may be used in order to predict the earthquake-induced ground motions expected from future earthquakes in the region surrounding Lake Van.
    Description: Published
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: open
    Keywords: Earthquake-induced ground motion, Lake Van, Crustal attenuation ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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