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  • 1
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    Can Hydrocarbon Extraction From the Crust Enhance or Inhibit Seismicity in Tectonically Active Regions? A Statistical Study in Italy (2021)
    Frontiers
    Details
    Publication Date: 2021-07-07
    Description: A number of oil- and gas-producing leases have been operating in Italy in the last decades, many of which are located in the surroundings of tectonically active regions. Identifying human-induced seismicity in areas with high levels of natural seismicity is a difficult task for which virtually any result can be a source of controversy. We implemented a large-scale analysis aiming at tracking significant departures of background seismicity from a stationary behavior around active oil and gas development leases in Italy. We analyzed seismicity rates before and after hydrocarbon peak production in six oil-producing and 43 gas-producing leases, and evaluate the significance of possible seismicity rate changes. In a considerable number of cases seismicity rate results stationary. None of the observed cases of seismicity rate increase after the peak production is statistically significant (at a s.l. = 0.05). Conversely, considering cases of seismicity rate decrease after peak production, our results suggest that the seismicity rate reduction is statistically significant (s.l. = 0.05) around one oil-producing lease (Val d’Agri, Basilicata) and around a cluster of gas-producing leases in Sicily. Our results put in evidence correlated changes between the rates of shallow seismicity and hydrocarbon production in these areas, which are then identified as hotspots requiring more detailed research; assessing actual causal relationships between these processes will require further physically-based modelling. If a physical causative link between these processes exists, then the observed seismicity rate reduction could either be due to increased seismicity during the progressive increase in production before reaching its maximum, or to an actual seismicity rate reduction after that peak. Considering that there is evidence of seismicity occurring before the start of hydrocarbon production, which contrasts with the evident reduction of events observed after the peak production, we think it likely that the seismicity inhibition is a plausible hypothesis. Using a simple model we also calculate Coulomb stress changes in planes optimally oriented for failure, and we show that under some conditions the inhibition of seismicity is feasible in at least one of these cases. We conclude that more efforts to study the mechanisms and the possible consequences of anthropogenically-driven seismicity inhibition are required.
    Description: This study was performed with the support of Clypea, the Innovation Network for Future Energy financed by the Italian Ministry of Economic Development, Direzione Generale per le Infrastrutture e la Sicurezza dei Sistemi Energetici e Geominerari (MISE—DGISSEG)
    Description: Published
    Description: 673124
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Keywords: regional seismicity ; hydrocarbon production ; correlation analysis ; seismicity rate changes ; Italy, ; anthropogenic hazards ; 04. Solid Earth
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Hybrid Broadband Seismograms for Seismic Shaking Scenarios: An Application to the Po Plain Sedimentary Basin (Northern Italy) (2020)
    Springer
    Details
    Publication Date: 2021-06-22
    Description: The densely populated Po Plain, a very deep sedi- mentary basin in northern Italy, is prone to heavy shaking during earthquakes. Seismic hazard assessment must account for local variation in wave amplification. Standard ground motion prediction equations may fail to picture the complexity of strong lateral gradients in seismic response, due to sharp structural heterogeneity. For this reason, there is an increasing demand for full waveform predictions for engineering applications. Here, we present an implementation of a hybrid broadband simulation based on the method of Mai et al. (Bull Seismol Soc Am 100(6):3338–3339, 2010), to obtain complete broadband seismograms of 0.1–10 Hz. With this method, low frequency (〈1 Hz) and high frequency (1–10 Hz) seismograms are simulated separately using a deter- ministic and a stochastic method, respectively. We apply the method to four events recorded within the Po basin, with magnitude ranging from Mw = 4.4 to Mw = 5.6. The low frequency (LF) simulation is performed using SPECFEM3D on a few test sub- surface velocity models. The three-dimensional velocity model MAMBo (Molinari et al. in Bull Seismol Soc Am 105(2A):753–764, 2015)—consisting of a detailed structural description of the basin, based on extensive active-source data, embedded within a regional 3D crustal model—provided the best results for broadband simulations that most closely corresponded with the observations. It performed better than an ambient noise tomography model with more accurate S-wave velocities but less well defined layer topographies, emphasizing the importance of first order velocity discontinuities. The high frequency (HF) seis- mograms are simulated using the multiple scattering approach of Zeng et al. (J Geophys Res Solid Earth 96(B1):607–619, 1991). The scattering coefficients are obtained by performing a non linear inversion for each station to find best fitting synthetic envelopes. HF energy is then combined at 1 Hz to match the amplitude and phase spectra of the LF signal. We are able to simulate full waveforms throughout the Po Plain, of which shaking duration matches observed data for stations located in the basin. Shaking amplitudes are generally overestimated in the low frequency simulation by the MAMBo velocity model. Updating the MAMBo velocity model with more accurate S-wave velocity information of the ambient noise tomography model should improve the fit in future simulations.
    Description: Published
    Description: 2181–2198
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Ground motion ; hybrid method ; sedimentary basin ; Seismic shaking scenario ; 04. Solid Earth
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Effects of the representation of the crustal structure on seismic wave propagation modeling on the continental scal (2011)
    American Geophysical Union, Fall Meeting 2009
    Details
    Publication Date: 2017-04-04
    Description: The representation of crustal structure in 3D numerical models often poses particular problems that are difficult to overcome. Practical implementations of an improved crustal model into efficient tools for seismic wave propagation modeling often fail to honor the strongly varying depth of the Moho discontinuity. The widely used Spectral Element Method (SEM) using hexahedral elements follows the compromise to approximate this undulating discontinuity with polynomials inside the elements. This solution is satisfactory when modeling seismic wave propagation on the global scale and limitedly to rather low frequencies, but may induce inaccuracies or artifacts when working at the continental scale, where propagation distances are in the order of a few hundred or thousand kilometers and frequencies of interest are up to 0.1 Hz. An alternative modeling tool for seismic wave propagation simulations is the Discontinuous Galerkin Finite Element Method (ADER-DG) that achieves high-order accuracy in space and time using fully unstructured tetrahedral meshes. With this approach strong and undulating discontinuities can be considered more easily by the mesh and modifications of the geometrical properties can be carried out rapidly due to an external mesh generation process. Therefore, we implement more realistic models for the European crust -- based on a new, comprehensive compilation of currently available information from diverse sources, ranging from seismic prospection to receiver functions studies -- in both, the SEM and ADER-DG codes, to study the effects of the numerical representation of crustal structures on seismic wave propagation modeling. We compare the results of the different methods and implementation strategies with respect to accuracy and performance. Clearly, an improved knowledge and detailed representation of the structure of the Earth's crust is a key requisite for better imaging of the mantle structure.
    Description: Published
    Description: San Francisco, California, USA
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: open
    Keywords: crust ; wave propagation ; ADER-DG ; SEM method ; Europe ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Poster session
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  • 4
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    Analysis of different discrete representations of the European crust for numerical wave propagation simulations (2011)
    EGU General Assembly
    Details
    Publication Date: 2017-04-04
    Description: Implementation of crustal structure challenges accuracy and efficiency of practical numerical solutions of the seismic wave equation. Extremely varying thickness of sedimentary layers and depth of Moho discontinuity create the need for finding viable compromises between speed and precision. We present a study of the influence of different numerical representations of crustal structure on synthetic seismograms. We focus our attention on the European continental scale and consider realistic models for the crust based on a new, comprehensive compilation of currently available information from diverse sources, ranging from seismic prospection to receiver function studies. We investigate different renditions of the Earth structure comparing two approaches: (i) computational meshes honoring the (laterally-varying) geometry of interfaces for a layered crust, and (ii) meshes smoothing out discontinuities of the crustal model within computational elements. The second approach results in computationally more efficient meshes, at the expense of some accuracy in the delineation of the structure, that is however known with some approximation. We compare seismograms, computed using different model discretization accuracies along 2D cross sections, to reference solutions derived from the most accurate structural representation. For the required seismic wave propagation simulations we use the Discontinuous Galerkin Finite Element Method (ADER-DG) providing high-order accuracy in space and time on unstructured meshes. With this approach strong and undulating discontinuities can be considered by the element interfaces and modifications of the geometrical properties can be carried out rapidly due to an external mesh generation process. We analyze the results of the different meshing strategies with respect to accuracy and computational effort. The analysis is based on time-frequency error measures of amplitude and phase misfits and aims at a clear definition of limits in the discretization approach of the crustal structure at the continental scale. Our results are crucial for the creation of computationally more demanding 3D tetrahedral meshes of the model of the European crust in order to understand how much structural detail has actually to be resolved to get sufficiently accurate synthetic data sets in a desired frequency band as this is essential to validate crustal models by comparisons to real seismic observations.
    Description: Published
    Description: Vienna, Austria
    Description: 3.1. Fisica dei terremoti
    Description: restricted
    Keywords: crust ; wave propagation ; ADER-DG ; misfit ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Poster session
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