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Spagnuolo, Elena
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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 AccessPast seismic slip-to-the-trench recorded in Central America megathrust(2017)
; ; ; ; ; ; ; ;; ;; ; ;The 2011 Tōhoku-Oki earthquake revealed that co-seismic displacement along the plate boundary megathrust can propagate to the trench. Co-seismic slip to the trench amplifies hazards at subduction zones, so its historical occurrence should also be investigated globally. Here we combine structural and experimental analyses of core samples taken offshore from southeastern Costa Rica as part of the Integrated Ocean Drilling Program (IODP) Expedition 344, with three-dimensional seismic reflection images of the subduction zone. We document a geologic record of past co-seismic slip to the trench. The core passed through a less than 1.9-million-year-old megathrust frontal ramp that superimposes older Miocene biogenic oozes onto late Miocene–Pleistocene silty clays. This, together with our stratigraphic analyses and geophysical images, constrains the position of the basal decollement to lie within the biogenic oozes. Our friction experiments show that, when wet, silty clays and biogenic oozes are both slip-weakening at sub-seismic and seismic slip velocities. Oozes are stronger than silty clays at slip velocities of less than or equal to 0.01 m s–1, and wet oozes become as weak as silty clays only at a slip velocity of 1 m s–1. We therefore suggest that the geological structures found offshore from Costa Rica were deformed during seismic slip-to-the-trench events. During slower aseismic creep, deformation would have preferentially localized within the silty clays.301 15 - 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 AccessEvoluzione della trazione dinamica sulla faglia durante i forti terremoti(2006-04)
; Spagnuolo, E.Nel presente lavoro la dinamica dei processi sismogenetici è stata studiata attraverso un metodo innovativo basato su una soluzione dell’equazione dell’elastodinamica che esprime lo sforzo di taglio agente sul piano di faglia come funzione della velocità di dislocazione e della sua evoluzione temporale. Il dato di ingresso della procedura numerica è quindi l’evoluzione nel tempo della velocità di dislocazione in ciascun punto del piano di faglia. Questo metodo permette di vincolare l’evoluzione della trazione in funzione del tempo e della posizione sulla faglia e consente quindi la stima dei principali parametri dinamici per terremoti reali. Il vantaggio di tale modello è che non viene imposta una legge costitutiva a priori. La procedura numerica è stata applicata a forti terremoti reali, per i quali sono disponibili i modelli cinematici che descrivono la propagazione della rottura cosismica, allo scopo di studiare il comportamento meccanico delle strutture sismogenetiche ed i meccanismi responsabili del rilascio di energia. L’applicazione del metodo ha prodotto risultati originali ed interessanti: gli andamenti della trazione in ciascun punto del piano di faglia, sia in funzione del tempo sia in funzione della dislocazione, mostrano l’andamento atteso in base all’interpretazione teorica del processo di propagazione della rottura cosismica, ovvero un chiaro andamento di tipo ‘dynamic weakening’. I parametri dinamici risultano ben vincolati, sebbene dipendenti dalla risoluzione dei modelli cinematici, e mostrano una distribuzione eterogenea sul piano di faglia. Un parametro molto importante ottenuto dagli andamenti della trazione dinamica è il breakdown work che, come definito da Tinti et al. (2005), fornisce una stima dell’energia spesa per far propagare il fronte di rottura. I valori ottenuti per i diversi terremoti sono in accordo con quelli pubblicati recentemente in letteratura (Rice et al., 2005; Tinti et al., 2005) e dimostrano che il breakdown work costituisce un contributo commensurabile alle stime dell’energia irradiata.302 861 - PublicationOpen AccessIntroduction of seismic source directivity on hazard map(2010-09-06)
; ; ; ; ;Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Herrero, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Spallarossa, D.;Università degli Studi di Genova, Dip.Te.Ris., Genova; ; ; The seismic hazard maps are mainly influenced by the uncertainty associated to the ground motion predictive equation (GMPE). This uncertainty represents the unexplained part of the ground motion and it is mostly related to the choice of the model’s variables. In fact the representation of the ground motion through the GMPEs is simple compared to the complexity of the physical process involved: if only the magnitude and distance are taken into account, GMPEs predicts isoseismals curves that are expected to be isotropic around the hypocenter or along the fault. Instead, the presence of a fault plane across which a process of failure in shear develops makes this general formulation reliable only on average. In fact this failure is responsible of an asymmetry in the seismic radiation known, since Ben-Menhaem (PhD1961), as directivity effect. While the general knowledge of the earthquakes is treated explicitly in the empirical prediction, specific trends like the directivity effects are hidden in the uncertainty sigma. A way to reduce the sigma is therefore to refine the seismic seismic source description inside the GMPEs (e.g. NGA project, Power et al, Earthquake Spectra, 2008). In this framework we propose a strategy to introduce the directivity in the GMPEs and to study its effect on uncertainties and on hazard maps. For this purpose, we have used two different directivity models acting on the GMPE as corrective factors: one proposed by Somerville et al. (Seis.Res.Lett.1997) and the other one proposed by Spudich and Chiou (Earthquake Spectra 2008).The first factor depends on geometrical parameters and comes from theoretical deduction. The second one includes many source parameters and it is a hybrid factor, which functional formulation is deduced from the theory, calibrated on synthetic simulations and scaled on data. The classic hazard equation is then adapted in order to increase the number of source parameters (i.e. adding one integral over the parametric space for each new variable involved) and taking into account the corrective factors for directivity (Spagnuolo, PhD2010). We present the comparisons of hazard maps depending on the directivity factor and on the probability density functions of the fault strike and of the rupture “laterality”.179 111 - PublicationOpen AccessFrictional Melting in Hydrothermal Fluid-Rich Faults: Field and Experimental Evidence From the Bolfín Fault Zone (Chile)(2021-07)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ;Tectonic pseudotachylytes are thought to be unique to certain water-deficient seismogenic environments and their presence is considered to be rare in the geological record. Here, we present field and experimental evidence that frictional melting can occur in hydrothermal fluid-rich faults hosted in the continental crust. Pseudotachylytes were found in the >40 km-long Bolfín Fault Zone of the Atacama Fault System, within two ca. 1 m-thick (ultra)cataclastic strands hosted in a damage-zone made of chlorite-epidote-rich hydrothermally altered tonalite. This alteration state indicates that hydrothermal fluids were active during the fault development. Pseudotachylytes, characterized by presenting amygdales, cut and are cut by chlorite-, epidote- and calcite-bearing veins. In turn, crosscutting relationship with the hydrothermal veins indicates pseudotachylytes were formed during this period of fluid activity. Rotary shear experiments conducted on bare surfaces of hydrothermally altered rocks at seismic slip velocities (3 m s-1) resulted in the production of vesiculated pseudotachylytes both at dry and water-pressurized conditions, with melt lubrication as the primary mechanism for fault dynamic weakening. The presented evidence challenges the common hypothesis that pseudotachylytes are limited to fluid-deficient environments, and gives insights into the ancient seismic activity of the system. Both field observations and experimental evidence, indicate that pseudotachylytes may easily be produced in hydrothermal environments, and could be a common co-seismic fault product. Consequently, melt lubrication could be considered one of the most efficient seismic dynamic weakening mechanisms in crystalline basement rocks of the continental crust.78 27 - PublicationRestrictedImplementing the Effect of the Rupture Directivity on PSHA for the City of Istanbul, Turkey(2016)
; ; ; ; ; ; ; In the present study, we improve the probabilistic seismic-hazard assessment (PSHA), taking into account fault rupture-related parameters that sensibly affect the azimuthal variability of the ground motion. The study area is the Marmara region (Turkey), characterized by one of the highest levels of seismic risk in Europe and the Mediterranean region. The seismic hazard in the city of Istanbul is mainly associated with two active fault segments having well-defined geometry, focal mechanism, and rate of activity. Deterministic dynamic models are also available in this area (Aochi and Ulrich, 2015) that aimed at evaluating the seismic potential of the Marmara region. These models provide the statistical distribution for the hypocenter position, which is particularly relevant for rupture directivity. The aim of this work is to incorporate all the available information about the seismic potential of the Marmara region in a PSHA framework. We use an analytical model for directivity (Spudich and Chiou, 2008; Spudich et al., 2013) to integrate rupture-related parameters inside the PSHA standard procedure. Because the directivity effect is conditional on the hypocenter position, which is not a priori known, we assume at first ad hoc Gaussian distributions centered in the western, eastern, or middle part of the two fault segments. Our results show that the correction for directivity introduces a significant contribution (up to 25% of relative increase at 2 s) to the hazard maps computed with the standard PSHA practice (given in terms of pseudospectral accelerations having 10% probability of exceedance in 50 years). The hazard maps sensibly change when we use the distribution for the hypocenter position informed by the statistical treatment of dynamic simulations. Thus, integrating new variables in the PSHA in combination with properly informed probability density functions is not only feasible, but also recommended for a comprehensive PSHA.675 7 - PublicationOpen AccessMeasuring fracture energy under coseismic conditions(2013-04)
; ; ; ; ; ; ; ; ; ; ; ; ; Experiments performed on rocks at deformation conditions typical of seismic slip, show an extremely low friction coefficient, the activation of lubrication processes and a power-law strength decay from a peak value to a residual, steady-state value. The weakening curve has an initially very abrupt decay which can be approximated by a powerlaw. The resulting experimental fracture energy (defined, for a given slip amount u, as the integral between the frictional curve and the minimum frictional level reached σf (u)) scales on most of the slip range as G ∝ u α, a power-law in some aspects in agreement with the seismological estimates of G0 ∝ u 1.28 proposed by Abercrombie and Rice (2005). The values of G and G0 are comparable for slips of about u = 1cm (G ≈ 104 J/m2 ). Both gradually increase with slip up to about 106 J/m2, however, it appears that fracture energy G0 is slightly larger than G in the range of slip 0.1 < u < 10. The effective G0 observed at the seismological scale should implicitly incorporate energy sinks other than frictional dissipation alone, which we discuss (anelastic damage due to high off-fault dynamic stress close to the rupture tip; dissipation during slip-localizing process within fault gouge of finite thickness; strain accomodating fault roughness at different scales). Since G0 is obtained by estimating the amount of dissipation with respect to strain energy and radiated energy, it will implicitly incorporate the sum of all dissipative processes due to rupture propagation and fault slip. From the comparison of G obtained in the lab and in earthquakes, it appears that friction alone explains most of the dissipation, except maybe at the larger magnitudes89 26 - 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 - PublicationRestrictedVariability of kinematic source parameters and its implication on the choice of the design scenario(2010)
; ; ; ; ; ; ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cirella, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Herrero, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Tinti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Pacor, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; ; ; ; ; Near-fault seismic recordings for recent earthquakes (Chi Chi earthquake, 1999, and Parkfield earthquake, 2004) show the high spatial heterogeneity of ground motion. This variability is controlled by fault geometry, rupture complexity, and also by wave propagation and site effects. Nowadays, the number of available records in the near-source region is still not enough to infer a robust parameterization of the ground motion and to retrieve multiparametric predictive equations valid at close distances from the fault. The use of a synthetic approach may help to overcome this limitation and to study the strong ground motion variability. In this article we focus on ground-motion dependence on different earthquakes breaking the same fault, as it has been rarely recorded by instruments. We model seismic scenarios from different rupture models of a fault similar to the 1980 Irpinia, Italy, earthquake source (Mw 6.9). A discrete wavenumber/finite element technique is used to compute fullwave displacement and velocity time series in the low-frequency band (up to 2 Hz). We investigate the variability of the ground motion as a function of different source parameters (rupture velocity, slip distribution, nucleation point, and source time function), whose values depend on the state of knowledge of the physical model driving the process. The probability density functions of the simulated ground-motion parameters, such as displacement response spectrum and peak ground velocity, are used to identify particular scenarios that match specific engineering requests.232 19 - PublicationOpen AccessEarthquakes in the Mantle? Insights From Rock Magnetism of Pseudotachylytes(2017)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ;Ultramafic pseudotachylytes have been regarded as earthquake fossils formed at mantle depths (i.e., >30 km). Here we show that pseudotachylytes hosted by ultramafic rocks from three localities have distinct magnetic properties. Fresh host peridotites contain only small amounts of coarse-grained magnetite. In contrast, the ultramafic pseudotachylytes contain variable amounts of significantly finer magnetite that formed coseismically through melting. Among each locality, magnetite abundance in the pseudotachylytes ranges over several orders of magnitude (4–2,000 ppm), and magnetic grain size varies considerably (from single domain to multidomain). Because the host peridotites are compositionally similar, the pseudotachylyte magnetic properties are interpreted to primarily reflect the physical and cooling conditions prevailing during seismic slip. Further, the examination of laboratory-produced ultramafic pseudotachylytes shows that quenching does not produce superfine magnetite. We hypothesize that the magnetic properties of ultramafic pseudotachylytes are controlled by fO2 and in consequence vary systematically with depth of formation. Therefore, these properties can be used to assess if the ruptures producing the earthquakes that these pseudotachylytes represent nucleated at actual mantle depths or at shallow depths during exhumation of mantle rocks. ©2017. American Geophysical Union. All Rights Reserved.131 26