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  • 1
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    Epistemic Uncertainties in Local Earthquake Locations and Implications for Managing Induced Seismicity (2020)
    Seismological Society of America
    Details
    Publication Date: 2020-07-07
    Description: Earthquake hypocentral location is perhaps the most classical problem in seismology, the solution of which is often affected by significant uncertainty. In monitoring the effects of underground anthropogenic activities, the earthquake hypocentral location, magnitude, and ground motions are important parameters for managing induced seismicity (as e.g., for operating traffic-light systems). Such decisional systems define the operative reactions to be enacted once an earthquake, exceeding some magnitude or ground-motion threshold, occurs within a monitoring volume defined in the neighborhood of a certain anthropogenic underground activity. In this case, a reliable evaluation of the hypocentral location, along with its uncertainty, becomes crucial for rational decision making. In this article, we analyze different sources of uncertainty that can be relevant for the determination of earthquake source locations, and introduce a logic-tree-based ensemble modeling approach for framing the problem in a decision-making context. To demonstrate the performance of the proposed approach, we analyze uncertainties in the location of a seismic event that occurred on 22 July 2019 within the perimeter of the monitoring domain defined in the Val d’Agri oil field (southern Italy). We cast the result as a model ensemble that allows us to obtain samples from a parent distribution that better represents both aleatory and epistemic uncertainties of the earthquake location problem. We find that often-neglected epistemic uncertainties (i.e., those that arise when considering alternative plausible modeling approaches or data) can be considerably larger and more representative of the state of knowledge about the source location, than the standard errors usually reported by the most common algorithms. Given the consequential repercussions of decision making under uncertainty, we stress that an objective evaluation of epistemic uncertainties associated with any parameter used to support decisional processes must be a priority for the scientific community.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 2
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    Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy (2015)
    Seismological Society of America
    Details
    Publication Date: 2015-02-17
    Description: We built a 3D seismic model of the Po Plain and neighboring regions of northern Italy, covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid. We started by collecting an extensive and diverse set of geological and geophysical data, including seismic reflection and refraction profiles, borehole logs, and available geological information. Major geological boundaries and discontinuities have thus been identified and mapped into the model. We used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness. Seismic‐wave properties have been assigned to each unit using a rule‐based system and, VP, VS, and ρ derived from other studies. Sedimentary strata, although with varying levels of compaction and hence material properties, may locally reach a thickness of 15 km and give rise to significant effects in seismic‐wave propagation. We have used our new model to compute the seismic response for two recent earthquakes, to test its performance. Results show that the 3D model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments, whereas paths outside the basin may be well fit by more homogeneous (1D) hard rock structure. We conclude that the new model is suited for simulation of wave propagation, mostly for T〉3  s, and may serve well as a constraint for earthquake location and further improvements via body‐ or surface‐wave inversion.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 3
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    Normal modes of a medieval tower excited by ambient vibrations in an urban environment (2021)
    Seismological Society of America
    Details
    Publication Date: 2021-12-22
    Description: We report on a passive seismic experiment on a historical tower in northern Italy. Assessment of dynamical properties of such structures is known to be very important to anticipate their response to possible earthquake excitation. We show how classical seismological analyses can image, in high definition and detail, many modes of vibration, continuously excited by background tremor due to vehicle traffic. Similarly to what Earth’s normal modes reveal, such information pose constraints on the elastic (and anelastic) structure of a building that, in the case of a historical edifice, are not generally known, because appropriate information on its fabrication and constitution is not available. Our case refers to the twelfth century, 97 m tall, Asinelli tower in Bologna (northern Italy)—the tallest slender masonry building in Europe. We detect and analyze several modes of free flexural vibration, besides compressional and torsional modes. Free vibrations occur with slightly different natural frequencies along two orthogonal directions, as a consequence of a discrepancy between centers of mass and stiffness. This is apparent by the splitting of frequencies of modes of vibration. For each mode, the polarization of particle motion shows that energy cyclically transfers between the two different degrees of freedom of the system. The spectral signature of the nearby Garisenda tower can also be recognized on the spectrum of Asinelli, and vice versa, but the frequencies differ, so there is no cross influence between the two. These data can be used to calibrate the parameters used for dynamic modeling, to investigate variations in time of the dynamic response, and to characterize the anthropogenic sources of ground motion to possibly mitigate their effects. Although the engineering community has extensively addressed the field of structural health monitoring with specific tools, we show that methods part of any seismologist toolbox can also provide detailed information about buildings that can be used for their numerical modeling.
    Description: Published
    Description: 315–327
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Analisi statistica dei microsismi di origine marina registrati alla stazione di Villasalto (CA) (2023)
    Gruppo Nazionale di Geofisica della Terra Solida
    Details
    Publication Date: 2023-02-06
    Description: La componente dominante gli spettri di rumore sismico di fondo si osserva a periodi di circa 6--9 secondi ed è normalmente attribuita ai microsismi marini. Abbiamo analizzato le registrazioni continue effettuate alla stazione MEDNET di Villasalto in Sardegna per studiarne le caratteristiche al variare del tempo. L'analisi dei dati sismologici, meteorologici e mareografici ha mostrato un incremento del livello dello spettro in occasione del transito di forti perturbazioni atmosferiche che causano aumento dell'altezza dell'onda marina. In questi casi si osserva una chiara polarizzazione del moto del suolo secondo orbite di Rayleigh. Statisticamente la direzione di provenienza di queste onde sismiche punta verso la zona dove si verifica l'aumento del moto ondoso. Le caratteristiche di polarizzazione e il loro comportamento al progredire della perturbazione confermano l'applicabilità del modello di Strobach al bacino Mediterraneo
    Description: Consiglio Nazionale delle Ricerche, Osservatorio Geofisico Sperimentale (Trieste)
    Description: Published
    Description: Roma (Consiglio Nazionale delle Ricerche) , Piazzale A. Moro 7
    Description: 1IT. Reti di monitoraggio e sorveglianza
    Keywords: Microsismi ; Rumore sismico ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 5
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    Imaging Upper-Mantle Anisotropy with Transdimensional Bayesian Monte Carlo Sampling (2024)
    Seismological Society of America
    Details
    Publication Date: 2024-04-09
    Description: Underdetermination is a condition affecting all problems in seismic imaging. It manifests mainly in the nonuniqueness of the models inferred from the data. This condition is exacerbated if simplifying hypotheses like isotropy are discarded in favor of more realistic anisotropic models that, although supported by seismological evidence, require more free parameters. Investigating the connections between underdetermination and anisotropy requires the implementation of solvers which explore the whole family of possibilities behind nonuniqueness and allow for more informed conclusions about the interpretation of the seismic models. Because these aspects cannot be investigated using traditional iterative linearized inversion schemes with regularization constraints that collapse the infinite possible models into a unique solution, we explore the application of transdimensional Bayesian Monte Carlo sampling to address the consequences of underdetermination in anisotropic seismic imaging. We show how teleseismic waves of P and S phases can constrain upper‐mantle anisotropy and the amount of additional information these data provide in terms of uncertainty and trade‐offs among multiple fields.
    Description: In press
    Description: OST1 Alla ricerca dei Motori Geodinamici
    Description: JCR Journal
    Keywords: 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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