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Bizzarri, Andrea
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Bizzarri, Andrea
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andrea.bizzarri@ingv.it
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staff
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B-5039-2010
70 results
Now showing 1 - 10 of 70
- PublicationOpen AccessCalculation of the local rupture speed of dynamically propagating earthquakes(2013-12)
; ;Bizzarri, A; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, ItaliaThe velocity at which a propagating earthquake advances on the fault surface is of pivotal importance in the contest of the source dynamics and in the modeling of the ground motions generation. The rupture speed (vr ) is one of the results provided by spontaneous dynamic models of ruptures, in that it is a part of the solution and it is not imposed a priori, like in non spontaneous models or in kinematic models. Since vr is numerically retrieved from the spatial distribution of the rupture times (tr ), a well– constrained value of vr in a given fault node is important. In this paper we focus on the numerical determination of vr. By comparing different numerical schemes to compute vr from tr we show that, in general, central finite differences schemes are more accurate than forward or backward schemes, regardless the order of accuracy. Overall, the most efficient and accurate algorithm is the five–points stencil method at the second–order of accuracy. These conclusions hold for homogeneous and heterogeneous configurations and for different constitutive models, such as the slip– weakening law and the rate– and state–friction governing equations. It is also shown how the determination of tr can affect vr; numerical results indicate that if the fault slip velocity threshold (vl ) used to define tr is too high (vl ≥ 0.1 m/s) the details of the rupture are missed, for instance the jump of the rupture front eventually occurring for 2–D supershear ruptures. On the other hand, for vl ≤ 0.01 m/s the results appear to be stable and independent on the choice of vl. Finally, it is confirmed that in the special case of the linear slip–weakening friction law the computation of vr from the threshold criterion on the fault slip velocity and from the achievement of the maximum yield stress are equivalent.308 156 - PublicationRestrictedEffects of permeability and porosity evolution on simulated earthquakes(2012-05)
; ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, ItaliaNumerical simulations are a fundamental tool to access the typical conditions attained during earthquake instabilities and to simulate the large number of dissipative processes taking places during faulting. In this study we consider a single-degree-of-freedom spring-slider system, a simplified fault model which can describe the whole seismic cycle and the dynamics of a fault with spatially homogeneous properties. We assume a rate- and state-dependent friction in which we incorporate the effects of pore fluid pressure, thermally-pressurized as a consequence of the frictional heat produced during sliding. We explore, in a single framework, the role of the time variations of the porosity, permeability or both, ultimately leading to changes in hydraulic diffusivity, which has been recognized as one of the key parameters in thermally-pressurized faults. Our synthetic ruptures show that the changes in the hydraulic diffusivity only due to porosity variations do not markedly affect the earthquake recurrence (cycle time), the traction evolution and the thermal history of the fault. On the contrary, when the evolutions of both the porosity and the permeability are accounted for, the cycle time is significantly reduced. This result has a clear implication in the context of the hazard assessment.189 21 - PublicationOpen AccessProceedings of the International School of Physics “Enrico Fermi”, Course 202 “Mechanics of Earthquake Faulting”(IOS Press, Amsterdam, 2019)
; ; ; ; ; 71 18 - PublicationOpen AccessComparison between Different heat source functions in thermal conduction problems(2010-12-06)
; Bizzarri, A.100 81 - PublicationOpen AccessIs the dependence on the temperature of the friction important in stress triggering phenomena? The case of the 2000 Iceland seismic sequence(2012-04)
; ; ; ; ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Crupi, P.; Università degli Studi di Bari ;de Lorenzo, S.; Università degli Studi di Bari ;Loddo, M.; Università degli Studi di Bari; ; ; We perform numerical experiments by using a mass–spring fault model subject to an external coseismic stress perturbation due to a remote seismic event happening on another fault, the causative fault. In particular, the aim of this study is to investigate the instantaneous fault interaction and possible triggering that happens when a fault perturbed by a stress change fails before the so–called unperturbed instability. As a realistic example we focus our attention on the instantaneous dynamic triggering phenomena occurred during the 17 June 2000 south Iceland seismic sequence in the South Iceland Seismic Zone (SISZ, Reykjanes Peninsula). The main event (Ms 6.6) was followed by three large events within a few tens of seconds (8, 26 and 30 s, respectively) located in a neighborhood of several tens of km. Among them the 26 s event was the best constrained (Bizzarri and Belardinelli, 2008). In the present study, conditions to simulate the instantaneous dynamic triggering connected to the former three events, have been investigated using the simple 1–D spring–slider analogue model representing a fault governed by the rate– and state–dependent friction laws. In previous studies suitable constitutive parameters of the modeled fault which allow the instantaneous triggering of the three events, have been found (Antonioli et al., 2006) and, furthermore, it was also shown how the dynamics of the 26 s event strongly depends on the assumed constitutive law and stress conditions (Bizzarri and Belardinelli, 2008) by considering the Dieterich–Ruina (DR henceforth) and the Ruina–Dieterich (RD henceforth) governing laws. In this context take place the present study original contribution that is to better understand if the conditions of instantaneous dynamic triggering (focusing on the case of the 26 s triggered event) provide any significant differences if modeled with a different rate– and state–dependent governing equation, the Chester and Higgs law (CH henceforth; see Chester and Higgs, 1992; Bizzarri, 2010b; Bizzarri, 2010c) which accounts for the thermal effect for frictional heating which may occur during seismic sliding.125 98 - PublicationOpen AccessDetermination of the temperature field due to frictional heating on a sliding interface(2010-09)
; ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, ItaliaIn the recent years we assisted to an increasing number of studies devoted to the quantification of the effects of temperature developed as a consequence of frictional heat on a sliding interface. The temperature field generated on the fault surface is responsible of a large number of physical and chemical dissipative process, summarized in Bizzarri (2010a). Among these we mention here the flash heating of micro–asperity contacts, basically consisting in a different behavior of fault friction at high fault slip velocities [e.g., Bizzarri, 2009a; Noda et al., 2009], the melting of rocks and gouge particles [Nielsen et al., 2008; Bizzarri, 2010b], the thermally–induced pressurization of fluids in saturated fault structures [Andrews, 2002; Bizzarri and Cocco, 2006; Rice, 2006]. A key issue of all these studies is the proper calculation of the temperature distribution on the fault surface and its temporal evolution. In this study we compare two different analytical solutions proposed in the literature with the special aim to clarify their prominent features, the numerical advantages and the different physical implications of each of them. In particular, we will compare the temporal evolution of the obtained temperature in the case of spontaneously spreading, fully dynamic rupture on a fault of finite width and we will show how the solutions can be reconciled.109 65 - PublicationOpen AccessPianificazione e gestione di un’emergenza sismica: esercitazione INGV del 26 novembre 2015 effettuata nell’ambito della Linea di Attività T5 “Sorveglianza sismica e operatività post terremoto”(INGV, 2016)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Amato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Massa, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Montone, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Crescimbene, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;La Longa, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Nella Struttura Terremoti dell’INGV la Linea di Attività T5 “Sorveglianza sismica ed operatività postterremoto” si occupa delle attività di sviluppo di strumenti e procedure per la valutazione in tempo reale degli effetti di terremoti e tsunami e della gestione delle emergenze sismiche. Uno dei suoi obiettivi del 2015 era la formalizzazione dei protocolli di intervento di Gruppi d’Emergenza, avvenuta per Emergeo, Emersito, IES, QUEST e Sismiko con Decreto del Presidente nel luglio 2015. Altro obiettivo era l’elaborazione di un Protocollo di Ente per la gestione delle emergenze sismiche. La bozza preparata nel 2015 prevede l’importante novità dell’Unità di Crisi, mai formalizzata in precedenza. Attraverso questo Protocollo di Ente si auspica di migliorare la risposta logistico-operativa dell’INGV durante l’emergenza, di avere una più rapida conoscenza del fenomeno in corso e di realizzare un’efficace comunicazione verso Protezione Civile, media e pubblico. Per verificare il tutto è stata organizzata un’esercitazione in cui è stato simulato un terremoto di magnitudo 6.4 nel basso Lazio. Si sono così sperimentate l’efficacia del flusso azioni/informazioni durante un’emergenza, il funzionamento dell’Unità di Crisi, la funzionalità dei protocolli dei Gruppi d’Emergenza, l’efficienza delle attività in sede per gli aspetti tecnico-logistici, il flusso di comunicazione interno e le comunicazioni istituzionali esterne (queste ultime simulate). In questo articolo sono descritte le fasi di organizzazione ed attuazione dell’esercitazione. Inoltre, durante il suo svolgimento, la valutazione dell’efficacia dell’organizzazione e delle attività svolte dai gruppi coinvolti è stata affidata ad alcuni osservatori e qui è allegata l’elaborazione dei commenti riportati. Abbiamo fatto infine una sintesi dei risultati positivi e delle criticità emerse dall’esercitazione, attività così importante a nostro avviso da considerarne indispensabile la ripetizione con cadenza quanto meno annuale.3550 438 - PublicationOpen AccessOn the slip-weakening behavior of rate- and state-dependent constitutive laws(2002-06-08)
; ; ;Cocco, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; We study the dynamic traction behavior within the cohesive zone during the propagation of earthquake ruptures adopting rate and state dependent constitutive relations. The resulting slip weakening curve displays an equivalent slip weakening distance (D0_eq), which is different from the parameter L controlling the state variable evolution. The adopted constitutive parameters (a, b, L) control the slip weakening behavior and the absorbed fracture energy. The dimension of the nucleation patch scales with L and not with D0_eq. We propose a scaling relation between these two lengthscale parameters which prescribes that D0_eq/L ~ 15.136 398 - PublicationOpen AccessOn the implementation of Absorbing Boundary Conditions in a Finite Difference code with conventional grid(2009-12)
; ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, ItaliaModern numerical experiments for the solution of the direct problem in Seismology (i.e., the elasto–dynamic problem for fault surfaces) require the use of advanced numerical algorithms, capable of capturing all the essential features of the physical problem and to properly resolve the characteristic temporal and spatial lengths. In realistic dynamic models the fault surfaces have dimensions of several kilometer, in both strike and dip directions (e.g., Bizzarri et al., 2009, among many others). The required resolution of the problem typically requires the adoption of spatial sampling of several meter and time steps of the order of fractions of millisecond. As a consequence, this results in numerical experiments with algebraic equations discretized over hundreds of mega–nodes (n x 108 nodes). In turn, in order to obtain results in affordable human–times, this requires the exploitation of symmetry conditions (see for instance Bizzarri, 2009 for further details) and the use of several code optimizations, as well as an efficient parallel programming. In addition to the grid dispersion phenomenon, intrinsically present in every numerical algorithm, another problem can affect the obtained solutions: the spurious reflections of signals originated from the boundaries of the computational domain. These reflections might introduce numerical artifacts into the computed solutions and constructively interfere, finally causing problematic oscillations. One way to solve this problem is to arbitrarily enlarge the size of the computational domain — ideally approaching the unbounded (with the exclusion of the free surface) medium — in order to delay the back propagating fronts originating from the model boundaries. This solution is theoretically optimal, but technically unpractical, since the size of the model can easily become larger than the available computational resources. A second possibility to assess the problem is to introduce some ad hoc conditions at (or near to) the boundaries of the computational domain, in order to cause the back propagating waves to be adequately small (ideally null) from a numerical point of view. In this study we present different numerical algorithms consisting in Absorbing Boundary Conditions (ABCs thereinafter) that can be efficiently used to reduce the boundary effects (i.e., the waves originated by a seismogenic fault of finite extension reflected back into the model by the boundaries of the computational domain). We also indicate how they can be proficiently implemented in a Finite Difference, conventional grid numerical FORTRAN code.153 97 - PublicationRestrictedWhat can physical source models tell us about the recurrence time of earthquakes?(2012-09)
; ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, ItaliaEarthquake prediction, no matter what the timescale, has been and continues to be a contentious subject and it is indubitably a prominent challenge for modern seismology and earthquake physics. Indeed, few natural events can have the catastrophic consequences of earthquakes (earthquakes today accounts for about 60 % of natural fatalities). A physical description of earthquake represents an amenable approach to the prediction, but it suffers of some limitations, basically due to the notorious ignorance about the initial state of a given fault and about the physical law controlling its traction evolution. Independently on those intrinsic, epistemic limitations, the concept of the earthquake recurrence, based upon the idea of the cyclic (or characteristic) earthquake, has been often invoked to describe (and thus to predict) subsequent instability events on a seismogenic structure. In this paper, by using the simplest analog fault model, the one–degree–of–freedom mass–spring system, we quantitatively show that the concepts of the recurrence time and the earthquake cycle have limitations (even not meaningless). We will discuss in a compendious synopsis all the possible physical mechanisms which can dramatically affect the recurrence time. Our conclusions emphasize again that the competing mechanisms potentially occurring during faulting, even in the simplest and idealized condition of an isolated fault, can significantly complicate the regular cyclicity of earthquakes predicted by the analog fault system. These conclusions can contribute to the debate about the role of the physical modelling of earthquakes in the contest of seismic hazard assessment.259 16