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Cirella, Antonella
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Cirella, Antonella
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antonella.cirella@ingv.it
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- PublicationOpen AccessJoint Inversion of Geodetic and Strong Motion Data for the 2012, Mw 6.1–6.0, May 20th and May 29th, Northern Italy Earthquakes: Source Models and Seismotectonic Interpretation(2023-04)
; ; ; ; ; ; ; ; ; Abstract We present the first rupture models of the two mainshocks of the 2012 northern Italy sequence, determined by jointly inverting seismic and geodetic data. We aim at providing new insights into the mainshocks for which contrasting seismotectonic interpretations are proposed in literature. Sources' geometric parameters were constrained by seismic reflection profiles, 3-D relocations and focal mechanisms of mainshocks/aftershocks. Site-specific velocity profiles were used to model accelerograms affected by strong propagation effects related to the Po basin. Our source models differ significantly from previous ones relying on either seismic or geodetic data. Their comparison against geological sections and aftershock distribution provides new insights about the ruptured thrust faults. The May 20th Mw6.1 mainshock activated the Middle Ferrara thrust-ramp dipping ∼45° SSW-wards, breaking a main eastern slip patch 4–15 km deep in Mesozoic carbonates (maximum slip 0.7–0.8 m) and Paleozoic-Triassic basement rocks, and a small western patch in the basement. The May 29th Mw6.0 mainshock featured two separated asperities along the Mirandola thrustramp dipping ∼42° S-wards: an eastern asperity 4–15 km deep in Mesozoic carbonates and basement rocks (maximum slip 0.7 m) and a deeper western one (7–16 km depth) mainly in the basement (slip peak 0.8 m). On-fault aftershocks were concentrated within the basement and Mesozoic carbonates, devoiding highslip zones. Slip and aftershock distribution was controlled by the rheological transition between Mesozoic carbonates and Cenozoic sediments. Unlike previous thin-skinned tectonic interpretations, our results point to a complex rupture process along moderately dipping (40°–45°) thrust-ramps deeply rooted into the Paleozoic crystalline basement. Plain Language Summary The two M6 mainshocks of the 2012 Italy sequence are the strongest earthquakes ever observed in the Po Plain, a strategic region for the Italian economy. The mainshocks ruptured blind thrust-faults, however their source models and seismotectonic interpretation are still debated because the thrust-system architecture is controversial. Contrasting thick-skinned and thin-skinned tectonic models are proposed. In thick-skinned interpretations, shortening is accommodated by thrust-ramps rooted into the crystalline basement that represent main seismogenic structures, whereas in thin-skinned interpretations, shortening and seismicity are controlled by listric faults splaying out from dècollement levels in the sedimentary crust. A comprehensive analysis of the mainshocks' source represents an opportunity to provide new insights into the seismogenesis in northern Italy and on a broader scale into seismotectonics of thrust-and-fold belts. We get a complete picture of the mainshocks kinematics by jointly inverting, for the first time, seismic and geodetic data, and unravel rupture heterogeneities not resolved by previous studies. By integrating source models with aftershock locations and geological models, we propose a comprehensive seismotectonic interpretation of the sequence. We conclusively identify the ruptured faults that correspond to thrust-ramps rooted into the crystalline basement and evidence the key role played by lithological changes in the rupture process.95 14 - PublicationOpen AccessThe EU Center of Excellence for Exascale in Solid Earth (ChEESE): Implementation, results, and roadmap for the second phase(2023)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ;; ; ;; ; ;; ;; ; ; ;; ; ; ; ; ;; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ;; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ;; ; ; ; ; ;; ; ; ;; ;; ; ; ; ;; ; ; ;; ;The EU Center of Excellence for Exascale in Solid Earth (ChEESE) develops exascale transition capabilities in the domain of Solid Earth, an area of geophysics rich in computational challenges embracing different approaches to exascale (capability, capacity, and urgent computing). The first implementation phase of the project (ChEESE-1P; 2018–2022) addressed scientific and technical computational challenges in seismology, tsunami science, volcanology, and magnetohydrodynamics, in order to understand the phenomena, anticipate the impact of natural disasters, and contribute to risk management. The project initiated the optimisation of 10 community flagship codes for the upcoming exascale systems and implemented 12 Pilot Demonstrators that combine the flagship codes with dedicated workflows in order to address the underlying capability and capacity computational challenges. Pilot Demonstrators reaching more mature Technology Readiness Levels (TRLs) were further enabled in operational service environments on critical aspects of geohazards such as long-term and short-term probabilistic hazard assessment, urgent computing, and early warning and probabilistic forecasting. Partnership and service co-design with members of the project Industry and User Board (IUB) leveraged the uptake of results across multiple research institutions, academia, industry, and public governance bodies (e.g. civil protection agencies). This article summarises the implementation strategy and the results from ChEESE-1P, outlining also the underpinning concepts and the roadmap for the on-going second project implementation phase (ChEESE-2P; 2023–2026).395 39 - PublicationOpen AccessEffect of Shallow Slip Amplification Uncertainty on Probabilistic Tsunami Hazard Analysis in Subduction Zones: Use of Long-Term Balanced Stochastic Slip Models(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The complexity of coseismic slip distributions influences the tsunami hazard posed by local and, to a certain extent, distant tsunami sources. Large slip concentrated in shallow patches was observed in recent tsunamigenic earthquakes, possibly due to dynamic amplification near the free surface, variable frictional conditions or other factors. We propose a method for incorporating enhanced shallow slip for subduction earthquakes while preventing systematic slip excess at shallow depths over one or more seismic cycles. The method uses the classic k−2 stochastic slip distributions, augmented by shallow slip amplification. It is necessary for deep events with lower slip to occur more often than shallow ones with amplified slip to balance the long-term cumulative slip. We evaluate the impact of this approach on tsunami hazard in the central and eastern Mediterranean Sea adopting a realistic 3D geometry for three subduction zones, by using it to model ~ 150,000 earthquakes with 𝑀𝑤 from 6.0 to 9.0. We combine earthquake rates, depth-dependent slip distributions, tsunami modeling, and epistemic uncertainty through an ensemble modeling technique. We found that the mean hazard curves obtained with our method show enhanced probabilities for larger inundation heights as compared to the curves derived from depth-independent slip distributions. Our approach is completely general and can be applied to any subduction zone in the world.1208 47 - PublicationOpen AccessThe 2018 Mw 6.8 zakynthos (Ionian Sea, Greece) Earthquake: Seismic source and local tsunami characterization(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; We investigated the kinematic rupture model of the 2018 Mw 6.8 Zakynthos, Ionian Sea (Greece), earthquake by using a non-linear joint inversion of strong motion data, high-rate GPS time series, and static co-seismic GPS displacements. We also tested inversion results against tide-gauge recordings of the small tsunami generated in the Ionian Sea. In order to constrain the fault geometry, we performed several preliminary kinematic inversions by assuming the parameter values resulting from different published moment tensor solutions. The lowest cost function values were obtained by using the geometry derived from the United States Geological Survey (USGS) focal solution. Between the two conjugate USGS planes, the rupture model which better fits the data is the one with the N9° E-striking 39°-ESE-dipping plane. The rupture history of this model is characterized by a bi-lateral propagation, featuring two asperities; a main slip patch extending between 14 and 28 km in depth, 9 km northeast from the nucleation and a slightly shallower small patch located 27 km southwest from the nucleation. The maximum energy release occurs between 8 s and 12 s, when both patches are breaking simultaneously. The maximum slip is 1.8 m and the total seismic moment is 2.4 × 1019 Nm, corresponding to a Mw value of 6.8. The slip angle shows a dominant right-lateral strike-slip mechanism, with a minor reverse component that increases on the deeper region of the fault. This result, in addition to the observed possibility of similar mechanisms for previous earthquakes occurred in 1959 and 1997, suggests that the tectonic deformation between the Cephalonia Transform Fault Zone and the northern tip of the Hellenic Arc Subduction zone may be accommodated by prevailing right lateral low-dipping faults, occurring on re-activated structures previously experiencing (until Pliocene) compressional regime. Comparison of predicted and observed tsunami data suggests the need of a better characterisation of local harbour response for this type of relatively short-wavelength events, which is important in the context of tsunami early warning. However, the suggested dominantly strike-slip character would in turn imply a reduced tsunami hazard as compared to a dominant thrust faulting regime from this source region.695 106 - PublicationOpen AccessProbabilistic Tsunami Hazard Analysis: High Performance Computing for Massive Scale Inundation Simulations(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Probabilistic Tsunami Hazard Analysis (PTHA) quantifies the probability of exceeding a specified inundation intensity at a given location within a given time interval. PTHA provides scientific guidance for tsunami risk analysis and risk management, including coastal planning and early warning. Explicit computation of site-specific PTHA, with an adequate discretization of source scenarios combined with high-resolution numerical inundation modelling, has been out of reach with existing models and computing capabilities, with tens to hundreds of thousands of moderately intensive numerical simulations being required for exhaustive uncertainty quantification. In recent years, more efficient GPU-based High-Performance Computing (HPC) facilities, together with efficient GPU-optimized shallow water type models for simulating tsunami inundation, have now made local long-term hazard assessment feasible. A workflow has been developed with three main stages: 1) Site-specific source selection and discretization, 2) Efficient numerical inundation simulation for each scenario using the GPU-based Tsunami-HySEA numerical tsunami propagation and inundation model using a system of nested topo-bathymetric grids, and 3) Hazard aggregation. We apply this site-specific PTHA workflow here to Catania, Sicily, for tsunamigenic earthquake sources in the Mediterranean. We illustrate the workflows of the PTHA as implemented for High-Performance Computing applications, including preliminary simulations carried out on intermediate scale GPU clusters. We show how the local hazard analysis conducted here produces a more fine-grained assessment than is possible with a regional assessment. However, the new local PTHA indicates somewhat lower probabilities of exceedance for higher maximum inundation heights than the available regional PTHA. The local hazard analysis takes into account small-scale tsunami inundation features and non-linearity which the regional-scale assessment does not incorporate. However, the deterministic inundation simulations neglect some uncertainties stemming from the simplified source treatment and tsunami modelling that are embedded in the regional stochastic approach to inundation height estimation. Further research is needed to quantify the uncertainty associated with numerical inundation modelling and to properly propagate it onto the hazard results, to fully exploit the potential of site-specific hazard assessment based on massive simulations.319 26 - PublicationOpen AccessVariability in synthetic earthquake ground motions caused by source variability and errors in wave propagation models(2019-06-24)
; ; ; ; ;; ; Numerical simulations of earthquake ground motions are used both to anticipate the effects of hypothetical earthquakes by forward simulation and to infer the behaviour of the real earthquake source ruptures by the inversion of recorded ground motions. In either application it is necessary to assume some Earth structure that is necessarily inaccurate and to use a computational method that is also inaccurate for simulating the wavefield Green's functions. We refer to these two sources of error as ‘propagation inaccuracies’, which might be considered to be epistemic. We show that the variance of the Fourier spectrum of the synthetic earthquake seismograms caused by propagation inaccuracies is related to the spatial covariance on the rupture surface of errors in the computed Green's functions, which we estimate for the case of the 2009 L'Aquila, Italy, earthquake by comparing erroneous computed Green's functions with observed L'Aquila aftershock seismograms (empirical Green's functions). We further show that the variance of the synthetic seismograms caused by the rupture variability (aleatory uncertainty) is related to the spatial covariance on the rupture surface of aleatory variations in the rupture model, and we investigate the effect of correlated variations in Green's function errors and variations in rupture models. Thus, we completely characterize the variability of synthetic earthquake seismograms induced by errors in propagation and variability in the rupture behaviour. We calculate the spectra of the variance of the ground motions of the L'Aquila main shock caused by propagation inaccuracies for two specific broad-band stations, the AQU and the FIAM stations. These variances are distressingly large, being comparable or in some cases exceeding the data amplitudes, suggesting that the best-fitting L'Aquila rupture model significantly overfits the data and might be seriously in error. If these computed variances are typical, the accuracy of many other rupture models for past earthquakes may need to be reconsidered. The results of this work might be useful in seismic hazard estimation because the variability of the computed ground motion, caused both by propagation inaccuracies and variations in the rupture model, can be computed directly, not requiring laborious consideration of multiple Earth structures.283 28 - PublicationOpen AccessHibrid broadband Ground-Motion Simulations for the 2016 Amatrice Earthquake, Central Italy, and Sensitivity of Ground-Motion to Earthquake Source Parameters(2018-09)
; ; ; ; ; ; ; ; ; On 24th August 2016 at 01:36 UTC a MW 6.0 earthquake struck several villages in central Italy, among which Accumoli, Amatrice and Arquata del Tronto. It caused 299 fatalities, major destruction and extensive damage in the surrounding area (up to 11 intensity degree). The earthquake was recorded by 350 digital accelerometers be- longing to the National Accelerometric Network (RAN) of the Italian Department of Civil Protection, to the National Seismic Network (Rete Sismica Nazionale, RSN) of the Istituto Nazionale di Geofisica e Vulcanologia (INGV), and to other local net- works. This earthquake ruptured a NW–SE oriented normal fault, according the prevailing extensional tectonics of the area.The maximum accelera- tion was observed at Amatrice station (AMT) with epicentral distance of 15 km, reaching 916 cm/s2 and 445.6 cm/s2 on E-W and N-S components, respectively. Motivated by the high levels of observed ground motion and damage, we have computed synthetics broadband time series for engineering purposes. To produce high-frequency seismograms, we have used a stochastic finite-fault model approach based on dynamic corner-frequency.121 137 - PublicationOpen AccessRupture Kinematics and Structural‐Rheological Control of the 2016 Mw 6.1 Amatrice (Central Italy) Earthquake From Joint Inversion of Seismic and Geodetic Data(2018)
; ; ; ; ; We investigate the rupture process of the 2016, Mw6.1 Amatrice earthquake, the first shock of a seismic sequence characterized by three damaging earthquakes occurred in Central Italy between August and October. We jointly invert strong motion, High-Rate GPS data, GPS and DInSAR displacements and we adopt ad-hoc velocity profiles of the crust below each station. The retrieved source model reveals a high degree of complexity, characterized by a prominent bi-lateral rupture with low slip at the hypocentre, two well-separated slip patches and a rupture front accelerating when breaking the largest patch. The rupture of the main asperity features a slip-velocity pulse that is impeded ahead of its current direction and splits into two pulses. In this fault section we find clues of structural and rheological control of the rupture propagation due to the fault system segmentation.279 49 - PublicationOpen Access
62 70 - PublicationRestrictedNear-source high-rate GPS, strong motion and InSAR observations to image the 2015 Lefkada (Greece) Earthquake rupture history(2017-09-04)
; ; ; ; ; ; ; ; ; ; ; ; ;; ;The 2015/11/17 Lefkada (Greece) earthquake ruptured a segment of the Cephalonia Transform Fault (CTF) where probably the penultimate major event was in 1948. Using near-source strong motion and high sampling rate GPS data and Sentinel-1A SAR images on two tracks, we performed the inversion for the geometry, slip distribution and rupture history of the causative fault with a three-step self-consistent procedure, in which every step provided input parameters for the next one. Our preferred model results in a ~70° ESE-dipping and ~13° N-striking fault plane, with a strike-slip mechanism (rake ~169°) in agreement with the CTF tectonic regime. This model shows a bilateral propagation spanning ~9 s with the activation of three main slip patches, characterized by rise time and peak slip velocity in the ranges 2.5-3.5 s and 1.4-2.4 m/s, respectively, corresponding to 1.2-1.8 m of slip which is mainly concentrated in the shallower (<10 km) southern half of the causative fault. The inferred slip distribution and the resulting seismic moment (M0 = 1.05 × 1019N m) suggest a magnitude of Mw6.6. Our best solution suggests that the occurrence of large (Mw > 6) earthquakes to the northern and to the southern boundaries of the 2015 causative fault cannot be excluded.554 5