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  • 1
    Publication Date: 2020-10-27
    Description: Recent studies on seismological data indicate that earthquake magnitude scales with either the dominant period or the peak amplitude in the seismogram’s first few seconds. At first sight, this may indicate that the earthquake’s final size is somehow related to the way rupture starts. One working hypothesis is that strong radiation from the initial phase of rupture is indicative of a triggering asperity releasing a consistent amount of elastic energy, with the potential to drive the fracture to large extents. We tested this concept with a number of numerical simulations, but within the models investigated, scaling was found only for ruptures extending up to about four times the size of the initial asperity; at larger distances the correlation was lost. Alternatively, a careful kinematic analysis of the earthquake source radiation shows that the initial signal recorded at any station does not necessarily correspond to the rupture initiation but may represent an extended portion of the radiating source. Using the concept of isochrones, we show that the apparent scaling may be explained by a simple kinematic model respecting causality, up to a given magnitude threshold where the scaling relation saturates. The saturation level is in agreement with that observed in some, but not all, of the real seismicity catalogs.
    Description: Published
    Description: 1-23
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: early warning ; earthquake magnitude ; 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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  • 2
    Publication Date: 2020-11-24
    Description: Apparent stress and corner frequencies are measured for the Chi-Chi, Taiwan sequence beginning with the Mw 7.6 mainshock on 20 September 1999. Using the coda source ratio method, we obtained stable source ratio estimates using broadband stations on Taiwan. We find the following: (1) For the mainshock and 3 of the larger aftershocks, apparent stress is clustered around 0.8 MPa (+/- 0.1 MPa); (2) Events below ~Mw 5.5 exhibit lower apparent stress with larger scatter, ranging between ~0.08 and 0.8 MPa and are spatially variable; 3) The Brune [1970, 1971] omega-square source model fits the spectral shape for events 4.7〈Mw〈7.6, however a step-wise break in self-similarity exists at ~Mw 5.5. We hypothesize that larger events are subject to the regional state-of-stress, whereas smaller aftershocks are sensitive to the local state-of-stress from stress-field redistribution following the mainshock and/or fault zone lubrication that affects only larger events.
    Description: Published
    Description: L10308
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Description: reserved
    Keywords: earthquake fault dynamics ; apparent stress ; dynamic stress drop ; 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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  • 3
    Publication Date: 2020-12-01
    Description: Se si vuole trattare fisicamente il fenomeno del terremoto `e necessario prima di tutto conoscere e poter rappresentare la sorgente dell’evento stesso e risalire in questo modo alla soluzione analitica del problema fisico. Una sorgente sismica pu`o essere identificata con una frattura nel mezzo (una faglia o parte di essa) che sottoposta ad una sollecitazione di sforzo disloca, ovvero accade che i due lembi della faglia si muovono l’uno rispetto all’altro. Questo tipo di sorgenti `e detta di taglio perch`e la dislocazione `e provocata da sforzi di taglio. Se il movimento relativo dei due lembi di faglia `e parallelo rispetto alla linea di rottura allora la faglia `e detta faglia trascorrente; se invece il movimento `e parallelo alla profondit`a della faglia questa `e detta faglia a rigetto verticale. Una dislocazione provoca nel mezzo circostante un campo degli spostamenti che pu`o essere studiato nel contesto della teoria dell’elasticit`a, come vedremo nel capitolo (2). In questa breve trattazione vogliamo rappresentare la sorgente sismica fisicamente e analiticamente e trattare la teoria principale che riguarda le sorgenti dei terremoti (capitolo (2), paragrafo (2.1), e capitoli (3) e (4)). Quindi vogliamo poter ricavare la descrizione esplicita dei campi di spostamento, di deformazione e di sforzo che essa genera nello spazio circostante (sezioni (2) e (2.5)). Nel capitolo (6) le conoscenze acquisite verranno tradotte in un codice di simulazione del comportamento di una particolare sorgente sismica. Questo permetter`a di visualizzare, attraverso delle mappe, il comportamento del mezzo circostante una faglia che disloca in termini di spostamento, deformazione e sforzo. La comprensione di come reagisce il mezzo circostante la sorgente sismica all’avvenire del terremoto `e importante per capire come diverse faglie interagiscono fra loro, favorendo o inibendo vicendevolmente la propria rottura. E’ comunemente noto nella letteratura specialistica che un terremoto generalmente ne favorisce altri intorno a s´e (i suoi aftershocks) ed `e questo il cosiddetto fenomeno di triggering; negli ultimi anni si fa pi`u attenzione anche al fenomeno opposto, ovvero al fatto che un terremoto ha anche la capacit`a di inibire per un periodo di tempo altri fenomeni in una certa zona (scaricandone lo sforzo accumulato). Quest’area si verr`a a trovare cos`ı in un periodo di cosiddetta quiescenza. Capire quindi come reagisce il mezzo ad una dislocazione `e importante se si vogliono sviluppare modelli di previsione a breve e lungo termine. La struttura della trattazione `e pensata per dare al lettore inizialmente un approccio pi`u concettuale di alcuni aspetti del problema proposto (in particolare della rappresentazione delle sorgenti), pur portando avanti la sua soluzione analitica; solo in un secondo momento vengono ripresi ed approfonditi, sia concettualmente che quantitativamente, alcuni degli argomenti proposti nella parte iniziale. Nella prima parte (capitolo (2)) ci riferiamo in particolare al pi`u semplice problema statico per un mezzo isotropo; in un secondo momento proponiamo alcuni teoremi fondamentali in una veste pi`u generale, includendo anche la variabile temporale e riferendoci ad un mezzo anisotropo (capitolo (4)). Vogliamo trattare, inoltre, le relazioni che intercorrono tra i principali parametri di sorgente e l’energia sismica (capitolo (5)). Infine, come gi`a accennato sopra, ci occupiamo di una specifica sorgente estesa di forma rettangolare di cui calcoliamo e rappresentiamo i relativi tre campi di spostamento, sforzo e deformazione su un piano, introducendola in un programma di simulazione (capitolo(6)).
    Description: Published
    Description: open
    Keywords: seismic source ; 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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  • 4
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    OGS, Universita' degli studi della Basilicata
    Publication Date: 2021-06-08
    Description: The Kobarid area (western Slovenia) was struck by two seismic sequences in 1998 and 2004. Corresponding mainshocks, occurred on April 12, 1998 and July 12, 2004, had magnitude MW =5.7 and MW =5.2, respectively and were located 2.6 km away from each other. Both of them were recorded by the Friuli-Venezia Giulia Seismometric Network, managed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), installed in north-eastern Italy (http://www.crs.inogs.it). During the sequences, the network recorded hundreds of aftershocks and both standard locations and duration magnitude (MD) estimations were performed. The seismic activity lasted 198 and 135 days, respectively and consisted of 700 events with MD in the range [1.5, 4.6] and 300 events with MD in the range [1.1, 3.6], respectively (Bressan et al., 2009). In this work, we estimate the seismic moment, M0, the corner frequency, fC, the Brune stress drop, ΔσB, the apparent stress, σa and the radiated energy, ES, of the mainshock and of 164 aftershocks of the Kobarid (2004) seismic sequence. The obtained results are compared with two previous analysis performed in the same region, concerning the source parameter scaling of the background seismicity (Franceschina et al., 2006) and of other seismic sequences (Bressan et al., 2007) occurred in the area.
    Description: MSP, EAGE, CODEVINTEC
    Description: Published
    Description: Potenza, Italy.
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: open
    Keywords: source parameters ; seismic sequence ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 5
    Publication Date: 2021-06-08
    Description: Source parameters of the mainshock (ML=5.3) and of 165 aftershocks (0.8 〈 ML 〈 3.5) of the 2004 Kobarid (Western Slovenia) seismic sequence are investigated in order to determine the corresponding source scaling relations. Data recorded from July to December 2004 by the Friuli and Veneto seismic network (FV), managed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) and installed in Northeastern Italy, are employed to obtain the SH-wave amplitude Fourier spectra of the selected earthquakes. For source spectra computation, we consider only records with significant values of the signal-to-noise ratio and, to account for local amplifications, we compute standard H/V spectral ratios (HVSR) for all the stations of the network. After correction for attenuation effects, source spectra obtained at stations with negligible site effects show a good fit with a ω-square model. We adopt different approaches to compute the source parameters and final results are chosen based on the obtained misfits between observed and theoretical source spectra. For 21 earthquakes of the sequence the obtained results are confirmed by the Empirical Green Function (EGF) technique, applied by estimating the spectral ratios of couples of events with hypocentral distance differences smaller than 500 m and magnitude differences greater than 1. The mainshock of the sequence is characterized by a seismic moment of 3.5x10^16 Nm and a corner frequency of 0.8 Hz, corresponding, in the Brune’s model (1970), to a fault radius of 1465 m and a stress drop of 4.9 MPa. Aftershocks have seismic moments in the range [3.3x10^11, 1.8x10^14] Nm, corner frequencies between 1.9 and 12.4 Hz (Brune radii between 95 and 638 m) and stress drops in the range [0.03, 1.55] MPa. The observed scaling of seismic moment (M0) with the local magnitude (ML) is consistent with the trend: Log M0 = 1.06 ML + 10.56. The Brune radius (rB) increases with the seismic moment according to: Log rB = 0.22 Log M0 - 0.40. Moreover, in spite of the high dispersion that characterizes the estimates of the Brune stress drop (ΔσB), we observe also an increase of ΔσB with M0. The mainshock is characterized by 2.4 x10^12 J radiated energy (ES) and 1.9 MPa apparent stress (σa). Aftershocks have energies between 2.0 x10^5 and 7.4 x10^8 J and apparent stress values increasing with the seismic moment in the range [0.01, 0.48] MPa. Radiated energies increase with seismic moments according to the empirical relationship: Log ES = 1.53 Log M0 - 12.47. The scaling of both ΔσB and σa with M0 in the range of magnitude between 0.8 to 5.3, evidences the non-self-similarity characteristics of the 2004 Kobarid seismic sequence. Similar results have been obtained by previous studies concerning the source parameter scaling of the background seismicity and of other seismic sequences of the area.
    Description: Published
    Description: 58-75
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquakes ; Source parameters ; Scaling law ; Seismic sequences ; Northeastern Italy ; Western Slovenia ; 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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  • 6
    Publication Date: 2020-09-29
    Description: This chapter summarizes a comparative study of shear-wave velocity models and seismic sources in the Campanian volcanic areas of Vesuvius and Phlegraean Fields. These velocity models were obtained through the nonlinear inversion of surfacewave tomography data, using as a priori constraints the relevant information available in the literature. Local group velocity data were obtained by means of the frequency–time analysis for the time period between 0.3 and 2 s and were combined with the group velocity data for the time period between 10 and 35 s from the regional events located in the Italian peninsula and bordering areas and two station phase velocity data corresponding to the time period between 25 and 100 s. In order to invert Rayleigh wave dispersion curves, we applied the nonlinear inversion method called hedgehog and retrieved average models for the first 30–35km of the lithosphere, with the lower part of the upper mantle being kept fixed on the basis of existing regional models. A feature that is common to the two volcanic areas is a low shear velocity layer which is centered at the depth of about 10 km, while on the outside of the cone and along a path in the northeastern part of the Vesuvius area this layer is absent. This low velocity can be associated with the presence of partial melting and, therefore, may represent a quite diffused crustal magma reservoir which is fed by a deeper one that is regional in character and located in the uppermost mantle. The study of seismic source in terms of the moment tensor is suitable for an investigation of physical processes within a volcano; indeed, its components, double couple, compensated linear vector dipole, and volumetric, can be related to the movements of magma and fluids within the volcanic system. Although for many recent earthquake events the percentage of double couple component is high, our results also show the presence of significant non-double couple components in both volcanic areas.
    Description: Published
    Description: 287-309
    Description: reserved
    Keywords: NONE ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
    Format: 8247786 bytes
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  • 7
    Publication Date: 2020-11-17
    Description: This article presents the results of a detailed study of the effects of the 1883 earthquake, which occurred at the island of Ischia (Gulf of Naples) and produced the total destruction of buildings in the epicentral area (Casamicciola town). Despite the moderate magnitude, this event was characterised by very high intensities (Imax = XI degree MCS) mainly due to the shallow depth of the source. The study of the earthquake shows that the intensities, which decreased rapidly with distance, were affected by source directivity, according to the causative fault geometry and tectonic structures, while local amplification of damage was observed where soft soils outcrop. The attenuation of seismic intensity with distance was evaluated using the well-known relation of intensity versus epicentral distance (Blake’s method). The diverse gradients of attenuation, observed in different directions, were ascribed to the various geological features of the shallow crust of the island. In order to evaluate the role of geology in the damage level, we computed different attenuation models for stiff and soft soils outcropping on the island. A systematic local amplification of about 1 MCS degree associated to the presence of reworked tuffs was obtained. This study also shows the influence of geological conditions on the evaluation of macroseismic data and supplies useful elements to derive a predictive map of potential site effects.
    Description: Published
    Description: id 231
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Description: reserved
    Keywords: Ischia island ; 1883 Earthquake ; Macroseismic data ; Site effects ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
    Publication Date: 2020-11-18
    Description: The anomaly of SLHF, which is a key component of the Earth's energy balance and represents the heat flux from the Earth's surface to the atmosphere associated with evaporation or transpiration of water on the surface and subsequent condensation of water vapor in the troposphere, has been widely reported as a possible earthquake precursor. The causes are generally attributed to the increase in infrared thermal (IR) temperature and the air ionization produced by increased emanation of radon from the Earth's crust. In this paper, the theoretical analysis and case study show that there is close relationship between soil moisture and SLHF anomalies. For inland earthquakes, the increase of soil moisture due to the rising of groundwater level will bring with higher potential evaporation, leading to the increase of latent heat flux. Further study with more accurate soil moisture product after the new satellite mission will help us to better understand the influence of soil moisture on SLHF variation and their relations with seismogenic process.
    Description: Published
    Description: Munich, Germany
    Description: 1.10. TTC - Telerilevamento
    Description: 3.1. Fisica dei terremoti
    Description: restricted
    Keywords: earthquake anomaly recognition (EAR) ; SLHF ; soil moisture lithosphere-coversphere-atmosphere (LCA) coupling ; 04. Solid Earth::04.02. Exploration geophysics::04.02.05. Downhole, radioactivity, remote sensing, and other methods ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 9
    Publication Date: 2021-02-17
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: We study how heterogeneous rupture propagation affects the coherence of shear– and Rayleigh–Mach wave fronts radiated by supershear earthquakes. We address this question using numerical simulations of ruptures on a planar, vertical strike–slip fault embedded in a three–dimensional, homogeneous, linear elastic half–space. Ruptures propagate spontaneously in accordance with a linear slip–weakening friction law through both homogeneous and heterogeneous initial shear stress fields. In the 3–D homogeneous case, rupture fronts are curved due to interactions with the free surface and the finite fault width; however, this curvature does not greatly diminish the coherence of Mach fronts relative to cases in which the rupture front is constrained to be straight, as studied by Dunham and Bhat (2008). Introducing heterogeneity in the initial shear stress distribution causes ruptures to propagate at speeds that locally fluctuate above and below the shear–wave speed. Calculations of the Fourier amplitude spectra (FAS) of ground velocity time histories corroborate the kinematic results of Bizzarri and Spudich (2008): 1) The ground motion of a supershear rupture is richer in high frequency with respect to a subshear one. 2) When a Mach pulse is present, its high frequency content overwhelms that arising from stress heterogeneity. Present numerical experiments indicate that a Mach pulse causes approximately an –1.7 high frequency falloff in the FAS of ground displacement. Moreover, within the context of the employed representation of heterogeneities and over the range of parameter space that is accessible with current computational resources, our simulations suggest that while heterogeneities reduce peak ground velocity and diminish the coherence of the Mach fronts, ground motion at stations experiencing Mach pulses should be richer in high frequencies compared to stations without Mach pulses. In contrast to the foregoing theoretical results, we find no average elevation of 5%–damped absolute response spectral accelerations (SA) in the period band 0.05–0.4 s observed at stations that presumably experienced Mach pulses during the 1979 Imperial Valley, 1999 Kocaeli, and 2002 Denali Fault earthquakes compared to SA observed at non–Mach pulse stations in the same earthquakes. A 20% amplification of short period SA is seen only at a few of the Imperial Valley stations closest to the fault. This lack of elevated SA suggests that either Mach pulses in real earthquakes are even more incoherent that in our simulations, or that Mach pulses are vulnerable to attenuation through nonlinear soil response. In any case, this result might imply that current engineering models of high frequency earthquake ground motions do not need to be modified by more than 20% close to the fault to account for Mach pulses, provided that the existing data are adequately representative of ground motions from supershear earthquakes.
    Description: Published
    Description: B08301
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Numerical modeling ; Supershear ruptures ; 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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  • 10
    Publication Date: 2021-05-12
    Description: Today, satellite remote sensing has reached a key role in Earth Sciences. In particular, Synthetic ApertureRadar (SAR) sensors and SAR Interferometry (InSAR) techniques are widely used for the study of dynamicprocesses occurring inside our living planet. Over the past 3 decades, InSAR has been applied for mappingtopography and deformation at the Earth’s surface. These maps are widely used in tectonics, seismology,geomorphology, and volcanology, in order to investigate the kinematics and dynamics of crustal faulting,the causes of postseismic and interseismic displacements, the dynamics of gravity driven slope failures,and the deformation associated with subsurface movement of water, hydrocarbons or magmatic fluids.
    Description: Published
    Description: 58-82
    Description: 1T. Geodinamica e interno della Terra
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: reserved
    Keywords: SAR ; InSAR ; Earth observation ; Surface displacements ; Satellite missions ; Advanced InSAR ; Earthquake studies ; Volcanic studies ; Tectonic process ; Coseismic studies ; Soil liquefaction ; Post-seismic studies ; Interseismic studies ; Volcanic unrest ; Pre-eruptive phase ; Eruptive phase ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.03. Geodesy::04.03.09. Instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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