1,721,062 research outputs found
Ground-motion predictive equations for low-magnitude earthquakes in the Campania–Lucania area, Southern Italy
No full textA key aspect of ground-shaking map calculation is represented by ground-motion predictive equations (GMPEs). In fact, ground-shaking maps obtained soon after an earthquake are calculated by integrating observed data and ground-motion estimates from GMPEs for those areas not covered by seismic stations. Empirical ground-motion models that are used to obtain these estimates refer primarily to strong ground-motion due to large earthquakes and cannot be properly used to estimate the effects of small magnitude seismic events. In this paper we calibrated GMPEs for low-magnitude earthquakes from data recorded at the seismographic stations of the Irpinia Seismic Network, in the Campania–Lucania region, Southern Italy. In particular, the available dataset is formed by peak ground acceleration (PGA) and velocity (PGV) parameters coming from 123 earthquakes (local magnitudes ranging between 1.5 and 3.2) recorded at 21 stations of the ISNet network at hypocentral distances from 3 km to about 100 km. The total number of peaks measurements is 875. This study is part of a research project, in collaboration with the Italian Department of Civil Protection and National Institute of Geophysics and Volcanology, aimed at producing ground-motion shaking maps
Slip imaging of the May 20, 2012, MW 5.8, Po Plain (Northern Italy) earthquake from the inversion of the source time functions
No full textNo abstrac
The signal to noise ratio and the completeness magnitude: The effect of COVID19
No full textWe analyse the earthquakes catalogues for Italy, South California, and Greece across the COVID-19 lockdown period for each country. The results for Italy and Greece show that, even if the reduction of the signal to noise ratio has improved the earthquake detection capability, the completeness magnitude remains substantially unchanged, making the improved detection capability ineffective from the statistical point of view. A slight reduction (0.2) of the completeness magnitude is observed for South California, likely related to the relatively higher number of seismic stations located close to urban areas. Our findings suggest that—given the present configuration of the seismic network considered here—only an important decrease in the station spacing can produce a significant decrease of the completeness magnitude
BISTROP: Bayesian inversion of spectral-level ratios and p-wave polarities for focal mechanism determination
No full textThe analysis of earthquake focal mechanisms provides information about the stress regime, fault geometry, and deformation processes acting in a given region. Generally, the techniques aimed at determining focal mechanism are designed to work in a specific magnitude range operating both in the time and frequency domain and using different data (e.g., P polarities, S-wave polarization, S/P-amplitude ratios, etc.). In this article, we present a new method, Bayesian inversion of spectral-level ratios and P-wave polarities (BISTROP), that can be applied to both small and moderate-to-large magnitude events. BISTROP uses a Bayesian approach to jointly invert the long-period spectral- level P/S ratios and the P polarities to infer the fault-plane solutions. We apply this method to analyze synthetic data as well as those generated by real earthquakes. We find that the obtained solutions for moderate earthquakes are comparable with those obtained using moment tensor inversion, and they are more constrained with respect to the solutions obtained using only P-polarity data for small earthquakes
The importance of mapping the design earthquake: insights for the southern apennines, Italy
No full textProbabilistic seismic hazard analysis is currently the soundest basis for the rational evaluation of ground-motion hazard for site-specific engineering design and assessment purposes. An increasing number of building codes worldwide acknowledge the uniform hazard spectra as the reference to determine design actions on structures and to select input ground motions for seismic structural analysis. This is the case, for example, in Italy where the new seismic code also requires the seismic input for nonlinear dynamic analysis to be selected on the basis of dominating events, for example, identified via disaggregation of seismic hazard. In the present study, the design earthquakes expressed in terms of representative magnitude (M), distance (R), and ε were investigated for a wide region in the southern Apennines, Italy. To this aim, the hazards corresponding to peak ground acceleration and spectral acceleration at 1 sec with a return period of 475 yr were disaggregated. For each of the disaggregation variables the shape of the joint and marginal probability density functions were studied. The first two modes expressed by M, R, and ε were extracted and mapped for the study area. The results shown provide additional information, in terms of source and ground-motion parameters, to be used along with the standard hazard maps to better select the design earthquakes. The analyses also allow us to assess how various frequency ranges of the design spectrum are differently contributed by seismic sources in the study area
Concentrated Slip and Low Rupture Velocity for the May 20, 2012, MW 5.8, Po Plain (Northern Italy) Earthquake Revealed From the Analysis of Source Time Functions
Full text linkWe analyse the rupture properties of the May 20, 2012, MW 5.8, Po Plain (Northern Italy) earthquake by using two different modeling procedures based on the source time functions: a forward modeling and a global inversion Bayesian method. While the forward modeling allows to retrieve general information on the source characteristics, the global inversion allows to explore a substantially larger number of possible solutions, with more parameters, providing a quantitative estimate of the misfit. We invert for the spatial slip distribution and for the rupture velocity on a planar fault model. The unknown slip is given at the nodes of the subfaults (control points) and then given at the elementary subfaults through a bilinear interpolation. The number of control points is progressively increased to move from a high‐ to low‐wavelength description of final slip on the fault plane. The optimal model parameter set is chosen according to the Akaike Information Criterion. The uncertainty on the slip distribution and rupture velocity has been estimated by a statistical analysis of the model ensemble and, in particular, through the weighted mean model and the standard deviation. We find that the most earthquake slip occurred in the regions located northeast and southwest of the hypocenter, consistent with the forward modeling. Moreover, we find a low rupture propagation velocity (0.4 compressional Mach number) similarly to what has been observed for the close 29 May, MW 5.6, and radiation efficiency suggesting that half of the strain energy was used to create new fracture
b value enlightens different rheological behaviour in Campi Flegrei caldera
No full textThe Campi Flegrei caldera is one of the most dangerous volcanoes in the world and since 2005 it is in unrest. Here we evaluate the 3D tomography of the b value at the Campi Flegrei volcanic area revealing a very good correlation with the structure of the hydrothermal system involved in the bradiseismic phenomenon. More precisely, we observe the smallest b-values where we expect the higher stress/strain concentration, namely in the caprock, and for the deepest seismicity. Conversely, the largest b values are observed where the porosity of the medium allows the passage of the volcanic gases toward the surface. Values of b close to typical tectonic ones are observed where the presence of faulting structures is well documented
b map evaluation and on-fault stress state for the Antakya 2023 earthquakes
No full textThe analysis of on-fault seismicity can enlighten the current stress state on the fault itself. Its definition is relevant to individuate fault patches that have not released all the accumulated stress even after the occurrence of a high magnitude earthquake. We use the b value to characterize the stress state on the fault of the Antakya 2023 main events, being b inversely proportional to the stress. The small magnitude seismicity occurring on the maximum slip fault-patches does not allow the b value estimation. This represents a strong indication that the maximum slip zone released most of the stress previously accumulated. Conversely, the lowest b values are located at the bends of the faults and close to the nucleation zone suggesting that, there, still exists not released stress implying that it could be reactivated in the future
The rule of dynamic strain to near source aftershock distribution of the 2014, Mw 6.0, Napa (California) earthquake
No full textThe rule of dynamic strain to near source aftershock distribution of the 2014, Mw 6.0, Napa (California) earthquak
Evaluation of the b Maps on the Faults of the Major (M > 7) South California Earthquakes
No full textWe use the Godano et al. (2022, ) method for evaluating the b maps of the faults associated with the largest earthquakes M >= 7.0 that occurred in California. The method allows an independent evaluation of the b parameter, avoiding the overlap of the cells and the omission of some earthquakes, while keeping all the available information in the catalog. We analyzed four large earthquakes: Landers, Hector Mine, Baja California, and Searles Valley. The maps obtained confirm that the b value can be considered as a strain meter and allow us to elucidate the presence of barriers, such as obstacles to the propagation of the fracture, on the fault of the analyzed earthquakes. A further estimated parameter is the time window during which aftershocks occur in the cell, Delta t. This quantity is very useful for a better definition of the aftershock generation mechanism. It reveals where the stress is released in a short time interval and how the complexity of the faulting process controls the occurrence of aftershocks on the fault, and also the duration of the entire sequence
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