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• 1
Unknown
Oxford University Press
Publication Date: 2019
Description: 〈span〉〈div〉SUMMARY〈/div〉We develop a probabilistic framework based on the conjunction of states of information between data and model, to jointly retrieve earthquake source parameters and anelastic attenuation factor from inversion of displacement amplitude spectra. The evaluation of the joint probability density functions (PDFs) enables us to take into account between-parameter correlations in the final estimates of the parameters and related uncertainties. Following this approach, we first search for the maximum of the 〈span〉a posteriori〈/span〉 PDF through the basin hopping technique that couples a global exploration built on a Markov chain with a local deterministic maximization. Then we compute statistical indicators (mean, variance and correlation coefficients) on source parameters and anelastic attenuation through integration of the PDF in the vicinity of the maximum likelihood solution. Definition of quality criteria based on the signal-to-noise ratio (SNR) and similarity of the marginal PDFs with a Gaussian function enable us to define the frequency domain for the inversion and to get rid of unconstrained solutions.We perform synthetic tests to assess theoretical correlations as a function of the SNR and to define the minimum bandwidth around the corner frequency for consistent parameter resolution.As an application, we finally estimate the source parameters for the 2016–2017 Central Italy seismic sequence. We found that the classical scaling between the seismic moment and the corner frequency holds, with an average stress drop of $\Delta \sigma = 2.1 \pm 0.3\,\,{\rm {MPa}}$. However, the main events in the sequence exhibit a stress drop larger than the average value. Finally, the small seismic efficiency indicates a stress overshoot, possibly due to dynamic effects or large frictional efficiency.〈/span〉
Print ISSN: 2051-1965
Electronic ISSN: 1365-246X
Topics: Geosciences
Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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• 2
Publication Date: 2019
Description: 〈p〉Burned skeletal remains are abundant in archaeological and paleontological sites, the result of fire or of ancient funerary practices. In the burning process, the bone matrix suffers structural and dimensional changes that interfere with the reliability of available osteometric methods. Recent studies showed that these macroscopic changes are accompanied by microscopic variations are reflected in vibrational spectra. An innovative integrated approach to the study of archaeological combusted skeletal remains is reported here, where the application of complementary vibrational spectroscopic techniques—INS (inelastic neutron scattering), FTIR (Fourier transform infrared), and micro-Raman—enables access to the complete vibrational profile and constitutes the first application of neutron spectroscopy to ancient bones. Comparison with data from modern human bones that were subjected to controlled burning allowed identification of specific heating conditions. This pioneering study provides archaeologists and anthropologists with relevant information on past civilizations, including regarding funerary, burial, and cooking practices and environmental settings.〈/p〉
Electronic ISSN: 2375-2548
Topics: Natural Sciences in General
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• 3
Unknown
Oxford University Press
Publication Date: 2019
Description: 〈span〉〈div〉Summary〈/div〉We develop a probabilistic framework based on the conjunction of states of information between data and model, to jointly retrieve earthquake source parameters and anelastic attenuation factor from inversion of displacement amplitude spectra. The evaluation of the joint probability density functions (PDFs) enables us to take into account between-parameter correlations in the final estimates of the parameters and related uncertainties. Following this approach, we first search for the maximum of the a-posteriori PDF through the basin hopping technique that couples a global exploration built on a Markov chain with a local deterministic maximization. Then we compute statistical indicators (mean, variance and correlation coefficients) on source parameters and anelastic attenuation through integration of the PDF in the vicinity of the maximum likelihood solution. Definition of quality criteria based on the signal to noise ratio and similarity of the marginal PDFs with a Gaussian function enable us to define the frequency domain for the inversion and to get rid of unconstrained solutions.We perform synthetic tests to assess theoretical correlations as a function of the signal to noise ratio and to define the minimum bandwidth around the corner frequency for consistent parameter resolution.As an application, we finally estimate the source parameters for the 2016–2017 Central Italy seismic sequence. We found that the classical scaling between the seismic moment and the corner frequency holds, with an average stress drop of $\Delta \sigma = 2.1 \pm 0.3\,\,MPa$. However, the main events in the sequence exhibit a stress drop larger than the average value. Finally, the small seismic efficiency indicates a stress overshoot, possibly due to dynamic effects or large frictional efficiency.〈/span〉
Print ISSN: 2051-1965
Electronic ISSN: 1365-246X
Topics: Geosciences
Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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• 4
Unknown
Oxford University Press
Publication Date: 2015-09-06
Description: The use of simulated accelerograms may improve the evaluation of the seismic hazard when an accurate modelling of both source and propagation is performed. In this paper, we performed broad-band simulations of the 2009, M 6.3 L'Aquila earthquake, coupling a k –2 kinematic model for the seismic source with empirical Green's functions (EGFs) as propagators. We extracted 10 EGFs candidates from a database of aftershocks satisfying quality criteria based on signal-to-noise ratio, fault proximity, small magnitude, similar focal mechanism and stress drop. For comparison with real observations, we also derived a low-frequency kinematic model, based on inversion of ground displacement as integrated from strong motion data. Kinematic properties of the inverted model (rupture velocity, position of the rupture nucleation, low-frequency slip and roughness degree of slip heterogeneity) were used as constraints in the k –2 model, to test the use of a single specific EGF against the use of the whole set of EGFs. Comparison to real observations based on spectral and peak ground acceleration shows that the use of all available EGFs improves the fit of simulations to real data. Moreover the epistemic variability related to the selection of a specific EGF is significantly larger (two to three times) than recent observations of between event variability, that is the variability associated with the randomness of the rupture process. We finally performed ‘blind’ simulations releasing all the information on source kinematics and only considering the fault geometry and the magnitude of the target event as known features. We computed peak ground acceleration, acceleration Fourier and response spectra. Simulations follow the same trend with distance as real observations. In most cases these latter fall within one sigma from predictions. Predictions with source parameters constrained at low frequency do not perform better than ‘blind’ simulations, showing that extrapolation of the low-frequency description of the rupture front as inferred by the kinematic inversion may introduce some bias in the final simulations.
Keywords: Seismology
Print ISSN: 0956-540X
Electronic ISSN: 1365-246X
Topics: Geosciences
Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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• 5
Unknown
Seismological Society of America (SSA)
Publication Date: 2015-10-02
Description: Ground-motion prediction equations (GMPEs) play a crucial role for estimating the seismic hazard in any region using either a deterministic or a probabilistic approach. Indeed, they represent a reliable and fast tool to predict strong ground motion, given source and propagation parameters. In this article, we estimated GMPEs for the South Korea peninsula. GMPEs were computed for peak ground displacement, peak ground velocity, peak ground acceleration, and spectral accelerations (damping at 5%) at 13 different periods from 0.055 to 5 s. We analyzed data from 222 earthquakes recorded at 132 three-component stations of the South Korea Seismic Network, from 2007 to 2012, with local magnitude ranging between 2.0 and 4.9 and epicentral distances varying from 1.4 to ~600 km. A nonlinear mixed effects technique is used to infer the GMPE coefficients. This technique includes both fixed and random effects and accounts for both inter- and intraevent dependencies in the data. Station-specific corrective coefficients were estimated by a statistical approach and were included in the final ground-motion prediction model. Finally, predictions for peak ground acceleration and spectral acceleration are compared with observations recorded for an M L  5.1 earthquake that occurred in 2014, the data for which were not included in the modeling. Online Material: Figures showing final ground-motion prediction equation models versus observations, and intra- and interevent residuals.
Print ISSN: 0037-1106
Electronic ISSN: 1943-3573
Topics: Geosciences , Physics
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• 6
Unknown
Oxford University Press
Publication Date: 2016-05-05
Description: We investigated the shallow structure of the Solfatara, a volcano within the Campi Flegrei caldera, southern Italy, using surface waves as a diagnostic tool. We analysed data collected during the RICEN campaign, where a 3-D active seismic experiment was performed on a dense regular grid of 90 m  x  115 m using a Vibroseis as the seismic source. After removal of the source time function, we analysed the surface wave contribution to the Green's function. Here, a 1-D approximation can hold for subgrids of 40 m  x  40 m. Moreover, we stacked all of the signals in the subgrid according to source–receiver distance bins, despite the absolute location of the source and the receiver, to reduce the small-scale variability in the data. We then analysed the resulting seismic sections in narrow frequency bands between 7 and 25 Hz. We obtained phase and group velocities from a grid search, and a cost function based on the spatial coherence of both the waveforms and their envelopes. We finally jointly inverted the dispersion curves of the phase and group velocities to retrieve a 1-D S -wave model local to the subgrid. Together, the models provided a 3-D description of the S -wave model in the area. We found that the maximum penetration depth is 15 m. In the first 4 m, we can associate the changes in the S -wave field to the temperature gradient, while at greater depths, the seismic images correlate with the resistivity maps, which indicate the water layer close to the Fangaia area and an abrupt variation moving towards the northeast.
Keywords: Seismology
Print ISSN: 0956-540X
Electronic ISSN: 1365-246X
Topics: Geosciences
Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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• 7
Publication Date: 2016-04-28
Description: Finite-fault earthquake source inversions infer the (time-dependent) displacement on the rupture surface from geophysical data. The resulting earthquake source models document the complexity of the rupture process. However, multiple source models for the same earthquake, obtained by different research teams, often exhibit remarkable dissimilarities. To address the uncertainties in earthquake-source inversion methods and to understand strengths and weaknesses of the various approaches used, the Source Inversion Validation (SIV) project conducts a set of forward-modeling exercises and inversion benchmarks. In this article, we describe the SIV strategy, the initial benchmarks, and current SIV results. Furthermore, we apply statistical tools for quantitative waveform comparison and for investigating source-model (dis)similarities that enable us to rank the solutions, and to identify particularly promising source inversion approaches. All SIV exercises (with related data and descriptions) and statistical comparison tools are available via an online collaboration platform, and we encourage source modelers to use the SIV benchmarks for developing and testing new methods. We envision that the SIV efforts will lead to new developments for tackling the earthquake-source imaging problem.
Print ISSN: 0895-0695
Electronic ISSN: 1938-2057
Topics: Geosciences
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• 8
Unknown
GFZ Data Services
Publication Date: 2020-02-12
Description: This data set contains continuous recordings of seismic noise, which have been made on the surface of a shallow volcanic crater in the Phlegrean Fields volcanic complex near Naples, Italy, where a significant level of volcanic-hydrothermal activity is presently concentrated (MED-SUV = Mediterranean Supersite Volcanoes). As part of the Phlegrean Fields, the Solfatara crater is a 0.4 × 0.5 km sub-rectangular structure whose geometry is mainly due to the control exerted by N40–50W and N50E trending normal fault systems, along which geothermal fluids can ascend. These systems crosscut the study area and have been active several times in the past.
Language: English
Type: info:eu-repo/semantics/workingPaper
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• 9
Unknown
In:  Seismological Research Letters
Publication Date: 2020-02-12
Type: info:eu-repo/semantics/article
Format: application/pdf
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• 10
Unknown
In:  Journal of Applied Geophysics
Publication Date: 2020-02-12
Type: info:eu-repo/semantics/article
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