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Spagnuolo, Elena
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Preferred name
Spagnuolo, Elena
Email
elena.spagnuolo@ingv.it
Staff
staff
ORCID
Scopus Author ID
36110318400
Researcher ID
E-1376-2017
63 results
Now showing 1 - 10 of 63
- PublicationOpen AccessFrictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O- and CO2- Rich Fluids(2018-06-28)
; ; ; ; ; ; ; ;; ; ; ; ;The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2O, pure CO2, and H2O + CO2 fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2 storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts. Seismic slip occurred at equivalent fluid pressures and normal stresses regardless of the fluid injected and degree of alteration of basalts. Injection of fluids caused also carbonation reactions and crystallization of new dolomite grains in the basalt-hosted faults sheared in H2O + CO2 fluid mixtures. Fast mineral carbonation in the experiments might be explained by shear heating during seismic slip, evidencing the high chemical reactivity of basalts to H2O + CO2 mixtures.143 14 - PublicationRestrictedEffect of water and rock composition on re-strengthening of cohesive faults during the deceleration phase of seismic slip pulses(2019)
; ; ; ; ; ; ; ; ; The elastic strain energy release rate and seismic waves emitted during earthquakes are controlled by the on-fault temporal evolution of the shear stress during rupture propagation. High velocity friction experiments highlighted that shear stress on the fault surface evolves rapidly during seismic slip pulses. This temporal evolution of shear stress is controlled by both fault weakening at seismic slip initiation and re-strengthening rate towards the end of slip. While numerous studies focused on fault weakening, less attention was given to co-seismic re-strengthening processes. Here we performed 53 friction experiments (normal stress ≤30 MPa, slip-rate ≤6.5 m s−1) imposing constant slip acceleration and deceleration (7.8 m s−2), on cohesive Carrara marble (99% calcite) and micro-gabbro (silicate-built rock) under dry, vacuum and water pressurized conditions. Microstructural observations showed that micro-gabbro accommodated seismic slip by bulk melting of the sliding surfaces, whereas Carrara marble by coupled decarbonation and grain-size dependent crystal plastic processes. Under room humidity conditions and low imposed power density (i.e., product of normal stress per slip rate), re-strengthening rate during the deceleration stage was up to ∼ 17 times faster in marble than in micrograbbro. In the latter, the re-strengthening rate increased slightly with the power density. The presence of water enhanced further this trend. On the contrary, in marbles the re-strengthening rate decreased drastically with power density and in the presence of water. Our experimental observations highlighted the first order importance of the mineralogy and rheology of the slip zone materials and, to a second order, of the presence of water in controlling co-seismic re-strengthening of faults during seismic slip deceleration.140 2 - PublicationOpen AccessUltra-thin clay layers facilitate seismic slip in carbonate faults(2017)
; ; ; ; ; ; ; ; ; ; ;; ; Many earthquakes propagate up to the Earth's surface producing surface ruptures. Seismic slip propagation is facilitated by along-fault low dynamic frictional resistance, which is controlled by a number of physico-chemical lubrication mechanisms. In particular, rotary shear experiments conducted at seismic slip rates (1 ms-1) show that phyllosilicates can facilitate co-seismic slip along faults during earthquakes. This evidence is crucial for hazard assessment along oceanic subduction zones, where pelagic clays participate in seismic slip propagation. Conversely, the reason why, in continental domains, co-seismic slip along faults can propagate up to the Earth's surface is still poorly understood. We document the occurrence of micrometer-thick phyllosilicate-bearing layers along a carbonate-hosted seismogenic extensional fault in the central Apennines, Italy. Using friction experiments, we demonstrate that, at seismic slip rates (1 ms-1), similar calcite gouges with pre-existing phyllosilicate-bearing (clay content ≤3 wt.%) micro-layers weaken faster than calcite gouges or mixed calcite-phyllosilicate gouges. We thus propose that, within calcite gouge, ultra-low clay content (≤3 wt.%) localized along micrometer-thick layers can facilitate seismic slip propagation during earthquakes in continental domains, possibly enhancing surface displacement.133 44 - PublicationOpen AccessInvestigating the effectiveness of rup- ture directivity during the August 24, 2016 Mw 6.0 central Italy earthquake(2016)
; ; ; ; ; In this study we investigate directivity effects associated to the August 24, 2016 Mw 6, central Italy earth- quake taking into account the source rupture heterogeneities. We use the directivity predictor proposed by Spudich et al. (2004) which is derived from the isochrones theory. The directivity is computed using a source to site geometry and a focal mechanism. For its simplicity it can be computed once that a moment tensor solution is available. We use this technique to validate the real time solutions. Moreover, because the directivity predictor depends on the rupture velocity it can be used as a proxy to validate the possible rupture history. For the aforementioned reasons our method revealed fruitful for real time applications and helpful to constrain a few main rupture features for further analysis.705 23 - PublicationOpen AccessAn empirically based steady state friction law and implications for fault stability(2016-04-16)
; ; ; ; ; ; ; Empirically based rate-and-state friction laws (RSFLs) have been proposed to model the dependence of friction forces with slip and time. The relevance of the RSFL for earthquake mechanics is that few constitutive parameters define critical conditions for fault stability (i.e., critical stiffness and frictional fault behavior). However, the RSFLs were determined from experiments conducted at subseismic slip rates (V < 1 cm/s), and their extrapolation to earthquake deformation conditions (V > 0.1 m/s) remains questionable on the basis of the experimental evidence of (1) large dynamic weakening and (2) activation of particular fault lubrication processes at seismic slip rates. Here we propose a modified RSFL (MFL) based on the review of a large published and unpublished data set of rock friction experiments performed with different testing machines. The MFL, valid at steady state conditions from subseismic to seismic slip rates (0.1 µm/s < V < 3 m/s), describes the initiation of a substantial velocity weakening in the 1-20 cm/s range resulting in a critical stiffness increase that creates a peak of potential instability in that velocity regime. The MFL leads to a new definition of fault frictional stability with implications for slip event styles and relevance for models of seismic rupture nucleation, propagation, and arrest.127 36 - PublicationOpen AccessFault Directivity and Seismic Hazard(2010-04)
; ;Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, ItaliaIn planning the design of structures in a region of potential seismic activity, a specification of the “strength” of the earthquake ground motion, or the most likelihood ground motion level, is needed. The earthquake occurrence, and its effects, is described as a stochastic process. Thus its realization is linked to state variables defined over a a known space through a continuous function. The Ground Motion Predictive Equation (GMPE) realize this function and, despite its shortcoming as an effective design tool to control damage (Priestly, 2003), it is still the most widely used representation of earthquake ground motion employed in engineering practice. As a consequence the majority of hazard estimations are based on the GMPE providing a ground motion specification as a function of a certain number of variables. In fact in many situation there are not enough data to allow a direct empirical specification of ground motion. Only few regions, i.e. Japan, have strong-motion network and data-banks sufficient to carry out seismic hazard assessment without the benefit of regionally-derived ground motion predictive model. The central role they hold in the hazard assessment motivates the recent efforts in better synthesize all available regional informations and general knowledge about earthquakes. The representation of the ground motion through the GMPE is simple compared to the complexity of the physical process involved. If only the magnitude and distance are taken into account, the GMPEs predict isoseismal curves that are expected to be isotropic around the hypocenter and uniform if no other effects are considered (i.e. site effects). Instead, the presence of a fault plane, across which a process of failure in shear develops, make this general formulation divert from the observations on a specific case. In fact the dynamic propagation of rupture results in anisotropy effects not included in the predictions although back-analyses of ground motions from past earthquakes have shown that such effects have a strong influence on the spatial distribution of ground motion.Although the anisotropy effects resulting from the propagation of rupture have been generally recognized and finally incorporated in predictions, its effect has not been tested yet in an hazard context. On the contrary, all the aforementioned issues motivate an in depth analysis of its contribution on the present tools of seismic hazard assessment. This work is mainly addressed to conduct such analysis. One guidance is provided answering to the following questions: Does directivity improves the performance of ground motion prediction in real time applications? Is directivity still effective in a PSHA framework? What deterministic hazard model can tell about directivity ?624 1353 - PublicationOpen AccessFluid pressurisation and earthquake propagation in the Hikurangi subduction zone(2021-04-30)
; ; ; ; ; ; ;; ;In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible for the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here, we show that at seismic velocity, shear-induced dilatancy is followed by pressurisation of fluids. The thermal and mechanical pressurisation of fluids, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.231 22 - PublicationRestrictedEffect of water on the frictional behavior of cohesive rocks during earthquakes(2013-12)
; ; ; ; ; ; ; ; ;Violay, M. E. S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Nielsen, S. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Gibert, B.; Géosciences Montpellier UMR5243, Université Montpellier, 2 Place Bataillon, 34095 Montpellier cedex 5, France ;Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cavallo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Azais, P.; Géosciences Montpellier UMR5243, Université Montpellier, 2 Place Bataillon, 34095 Montpellier cedex 5, France ;Vinciguerra, S.; Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via Valperga Caluso 35, 10125 Turin, Italy ;Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; ; Fluid-rock interactions can control earthquake nucleation and the evolution of earthquake sequences. Experimental studies of fault frictional properties in the presence of fl uid can provide unique insights into these interactions. We report the fi rst results from experiments performed on cohesive silicate-bearing rocks (microgabbro) in the presence of pressurized pore fl uids (H2 O, drained conditions) at realistic seismic deformation conditions. The experimental data are compared with those recently obtained from carbonate-bearing rocks (Carrara marble). Contrary to theoretical arguments, and consistent with the interpretation of some fi eld observations, we show that frictional melting of a microgabbro develops in the presence of water. In microgabbro, the initial weakening mechanism (fl ash melting of the asperities) is delayed in the presence of water; conversely, in calcite marble the weakening mechanism (brittle failure of the asperities) is favored. This opposite behavior highlights the importance of host-rock composition in controlling dynamic (frictional) weakening in the presence of water: cohesive carbonate-bearing rocks are more prone to slip in the presence of water, whereas the presence of water might delay or inhibit the rupture nucleation and propagation in cohesive silicate-bearing rocks.348 98 - PublicationRestrictedG: Fracture energy, friction and dissipation in earthquakes(2016)
; ; ; ; ; ; ; ; ; ; ; Recent estimates of fracture energy G ′ in earthquakes show a power-law dependence with slip u which can be summarized as G ′ ∝ u a where a is a positive real slightly larger than one. For cracks with sliding friction, fracture energy can be equated to G f : the post-failure integral of the dynamic weakening curve. If the dominant dissipative process in earthquakes is friction, G ′ and G f should be comparable and show a similar scaling with slip. We test this hypothesis by analyzing experiments performed on various cohesive and non-cohesive rock types, under wet and dry conditions, with imposed deformation typical of seismic slip (normal stress of tens of MPa, target slip velocity > 1 m/s and fast accelerations ≈ 6.5 m/s2). The resulting fracture energy G f is similar to the seismological estimates, with G f and G ′ being comparable over most of the slip range. However, G f appears to saturate after several meters of slip, while in most of the reported earthquake sequences, G ′ appears to increase further and surpasses G f at large magnitudes. We analyze several possible causes of such discrepancy, in particular, additional off-fault damage in large natural earthquakes.86 3 - PublicationOpen AccessLa distribuzione del radon indoor in alcuni settori della città di Roma. Ricercatori e studenti in un progetto innovativo: dalla raccolta del dato alla stesura di un articolo scientifico(2020-01)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; All’interno dei percorsi forma vi di Alternanza ScuolaLavoro un gruppo di ricercatori dell’Istituto Nazionale di Geofisica e Vulcanologia ha proposto e sviluppato con una terza classe del Liceo Scientifico Cavour di Roma un progetto riguardante l’avvicinamento degli studenti al mondo della ricerca scientifica, allo scopo di affrontarla e svilupparla in tu e le sue fasi. Dopo aver spiegato e condiviso l’obiettivo della ricerca con gli alunni, la prima fase del progetto ha riguardato la raccolta dei da tramite l’utilizzo di strumenti di misura; si è in seguito proceduto all’analisi dei dati ottenuti , attraverso un foglio elettronico di calcolo, la produzione di grafici e mappe tema che e infine la scrittura di un articolo scientifico (parte essenziale del lavoro del ricercatore) con la descrizione della ricerca svolta e dei risultati ottenuti . La ricerca ha riguardato la distribuzione del radon indoor in alcuni rioni di Roma. Gli studenti hanno avuto la possibilità di misurare il radon indoor tramite strumenti specifici nelle loro abitazioni e nella loro scuola, di analizzarne la distribuzione spaziale e temporale e di individuare dei casi particolarmente anomali. Sono stati quindi evidenziati i legami tra i valori misura , la geologia del sottosuolo e le tipologie abitative, illustrate per mezzo di mappe tematiche, facendo confluire il tutto o nella scrittura di un articolo scientifico. Il presente rapporto tecnico è stato introdotto dai ricercatori e sviluppato dagli studenti .889 162