Search

Some of the most relevant seismogenic sources in north-eastern Italy, western Slovenia and southern Austria have been studied in the framework of the Interreg IV A HAREIA (Historical And Recent Earthquakes in Italy and in Austria) project. Based on active fault data and historical records we have produced several ground shaking scenarios for some of the biggest known historical earthquakes that have occurred in the studied area. In particular, we compute the maximum peak ground velocity value at 1 Hz (PGV1Hz) for all studied events at every point of the computation grid, which covers the entire area of interest. For each studied earthquake we, then, make a qualitative comparison between the related observed intensity data points and computed scenarios, and select the one that is most consistent. This allows us to determine both the causative fault model and the approximate extended-fault rupturing process at the basis of each earthquake. We have applied this analysis to know historical events such as the Villach (1348), Idrija (1511), Asolo (1695) and Tyrol (1572, 1670, and 1689) earthquakes. We have added to the results obtained from these events several scenarios related to other important events that occurred or we deem possible to occur in the area and for which the causative fault is known. The maximum value obtained from all computed scenarios at a given grid point allows finally the construction of a PGV1Hz map for the area under investigation. Such a map, a main result of this study, can be used as a conservative

This paper gives short comments on the seismotectonic, seismological, and seismic hazard characteristics of the area of the nuclear power plant (NPP) of Krško (Slovenia). The plant was designed in the second half of the 1970s with no related probabilistic seismic hazard studies. The design was based on Regulatory Guides of 1973 with response spectra anchored to the peak ground acceleration of 0.30 g on the free field. The construction of a new NPP in the area is being taken into consideration by international investors. The Krško NPP is located inside a seismically active area, in which low-to-medium magnitude earthquakes have occurred in the last centuries. The greatest intensity felt near the NPP site was VIII for a local MW 5.7 - 6.2 earthquake in 1917, and the strongest event in the region was the M ≈ 6.3 Zagreb, 1880 event, whose epicentre was about 65 km from the NPP. The plant is close to some faults with unresolved neotectonic activity in the post-glacial epoch (18,000 years). Some stress test results from the 1990s would have suggested that 0.3 g were adopted at -20 m depth, corresponding to an effective value of 0.6 g at zero depth; this aspect is also commented. Finally, the difficult problem of estimating the maximum credible magnitude, Mmax, for very long return periods is addressed, based on the geological evidence provided by Geomatrix Consultants Inc. in 2004. From an apparent rupture length of 40 km of the Orlica fault, an Mmax of at least 7.2 could be hypothesized (1 st. dev. included). This hypothesis has anyway a low reliability, because the extent of the spatial continuity of the Orlica fault is still debated.

A fast seismic data analysis is essential to provide useful information to Authorities which make decisions immediately after a strong earthquake occurrence. During a strong earthquake, the modern accelerometers are the only instruments which can provide near source high-quality data that are important both for scientific and for civil protection purposes. Automatic and fast techniques have been developed by the University of Trieste for the automatic real-time strong motion data analysis. These techniques have been installed and optimized in the data acquisition centre of the Department of Civil Protection of Italy (DPC) to process the quasi real-time data of the National Accelerometric Network (RAN). RAN counts more than 450 stations covering all the Italian territory. Two local networks, the Friuli Venezia Giulia Accelerometric Network (RAF), located in NE Italy, and the Irpinia Seismic Network (ISNet), contribute their data into the RAN data acquisition system. 148 stations of the integrated RAN triggered the main shock of the Ferrara arc 2012 sequence. The RAN stations recorded the strong motions of the ML 5.9 mainshock, as well as of the major ML 4.1 foreshock and of nearly 35 aftershocks of magnitude ML ¡Ý 4.0. Soon after the mainshock, the DPC installed 15 temporary stations to increase the network coverage in the epicentral area. The performance of the network and of the fast automatic strong motion data analysis during the 2012 Ferrara sequence is analysed. The value of the strong motion parameters calculated by means of the automatic procedure immediately after the events show small differences with respect to the visual inspection procedure. Other aspects related to the seismic source, attenuation of seismic waves, directivity effects and to the comparison between distribution and attenuation of earthquake engineering parameters and observed damage are discussed, highlighting the robustness of the proposed automatic procedure.

Il Passo della Morte si trova nelle Alpi Carniche, in sinistra idrografica del fiume Tagliamento, tra gli abitati di Forni di Sotto e Ampezzo. È stato coinvolto nel passato da diversi fenomeni gravitativi importanti tra cui la frana di Sacrovint (Martinis, 1985) e attualmente risulta coinvolto in una deformazione gravitativa profonda di versante (DGPV) che coinvolge notevoli volumi di roccia (Massari et al., 2003; Bacchini, 2003; Marcato et al. 2005; Marcato, 2007). Il rischio associato a questo fenomeno è dato dall’interferenza con un’importante strada statale (S.S. 52) che attraversa la DGPV con due gallerie (la vecchia galleria del Passo della Morte e la nuova galleria di S. Lorenzo) e con il fiume Tagliamento che scorre ai piedi del versante. La parte più occidentale, attraversata dalla vecchia galleria del Passo della Morte, è però quella che desta le maggiori preoccupazioni a causa della possibile rapida evoluzione del fenomeno. Le peculiari caratteristiche dell’ammasso roccioso che la costituiscono, quali stratificazione verticale, deboli proprietà dei materiali interposti, denso sistema di discontinuità, fratture e piccole faglie, creano le condizioni ideali per l’innesco di fenomeni gravitativi. I possibili scenari dell’evoluzione di questo versante roccioso sono: il crollo o lo scivolamento di blocchi di piccoli volumi (1 m3) oppure la rottura per inflessione di parte o dell’intera massa calcarea, stimata in 500000 m3 (Codeglia, 2011). Il presente studio si è concentrato solo sulla porzione più occidentale della DGPV, cercando di caratterizzare l’ammasso roccioso attraversato dalla vecchia galleria. Le tecniche applicate sono state: un innovativo sistema di monitoraggio dell’attività microsismica, un’indagine georadar e di sismica attiva e l’analisi degli effetti di sito.

On 2005 February 22, the Dahuiyeh-Zarand earthquake, Mw 6.5, struck one of the most seismically active regions in south-central Iran, east of Zarand City in Kerman province,causing more than 500 fatalities. The causative fault of the 2005 Dahuiyeh-Zarand earthquake, a reverse fault, striking nearly EW and dipping to the north, was located within a mountainous region and therefore more difficult to identify compared to the range-bounded faults. Its identification, after the 2005 event, is very important for both the estimation of seismic hazard as well as for the damage and fatality functions. We have inverted six three-component nearfield strong motion waveforms to obtain the complete earthquake rupture history and slip distribution. Accelerograms are bandpass filtered with 0.2–1.0 Hz, and a length of 15–17 s of the waveforms is inverted. The lack of absolute timing has been successfully overcome by estimating, from the velocity model of the region, the propagation of P and S waves from the epicentre to the stations. The final fault slip model and the estimated source parameters are able to explain the observed waveforms. The rupture is found to be bilateral with a maximum slip of 2.4 m concentrated on two asperities in the west and east sides of the nucleation point at depths of 6–12 km. The western asperity is located to the east of Zarand City and beneath the Dahuiyeh village, which might explain why the Dahuiyeh village was totally destroyed by this earthquake.

The aim of this study is the real-time generation of ShakeMaps in the southeastern Alps area. The ShakeMap software has been adapted to the southeastern Alps region and implemented to obtain a stable interface with the Antelope acquisition system in order to extract the ground-motion parameters from the waveforms and to generate ShakeMaps within 5 min of the earthquake occurrence. To evaluate the influence of the station density, synthetic seismograms are computed for the Bovec (northwest Slovenia) 2004 earthquake, and various ShakeMaps are generated by varying the grid size of the simulated recording stations. The results indicate that a dense and uniform spatial distribution of stations in the field is essential to produce accurate ShakeMaps, and the present density of stations in central Friuli is sufficient for a reliable estimate of the extent of the area of strongest shaking. The related maps are generated in real time or quasi-real time using the region-specific ground-motion predictive equations and empirical relations that predict the macroseismic intensity from the recorded ground motion. The model is validated by comparison between observed data and ShakeMap results for both weak motions (Claut 2007 earthquake) and strong motions (Bovec 1998 earthquake).

The maximum expected ground motion in Greece is estimated for shallow earthquakes using a deterministic seismic hazard analysis (DSHA). In order to accomplish this analysis the input data include an homogeneous catalogue of earthquakes for the period 426 BC–2003, a seismogenic source model with representative focal mechanisms and a set of velocity models. Because of the discrete character of the earthquake catalogue and of errors in location of single seismic events, a smoothing algorithm is applied to the catalogue of the main shocks to get a spatially smoothed distribution of magnitude. Based on the selected input parameters synthetic seismograms for an upper frequency content of 1 Hz are computed on a grid of 0.2°×0.2°. The resultant horizontal components for displacement, velocity, acceleration and DGA (Design Ground Acceleration) are mapped. The maps which depict these results cannot be compared with previously published maps based on probabilistic methodologies as the latter were compiled for a mean return period of 476 years. Therefore, in order to validate our deterministic analysis, the final results are compared with PGA estimated from the maximum observed macroseismic intensity in Greece during the period 426 BC–2003. Since the results are obtained for point sources, with the frequency content scaled with moment magnitude, some sensitivity tests are performed to assess the influence of the finite extent of fault related to large events. Sensitivity tests are also performed to investigate the changes in the peak ground motion quantities when varying the crustal velocity models in some seismogenic areas. The ratios and the relative differences between the results obtained using different models are mapped and their mean value computed. The results highlight the importance in the deterministic approach of using good and reliable velocity models. © 2007 Elsevier B.V. All rights reserved.

International audience; Ground motion simulation methods, such as the finite-difference method (FDM) or the modal summation technique, require a model of the crustal structure through which the seismic waves pass in terms of density, velocity and attenuation parameters, such as Q. The use of such structural models within simulations means that travel path effects, such as the constructive interference of different phases, can be modelled. Currently one-, two- or three-dimensional models are used without much description of the benefits of using a particular dimension of model. Within FDMs, a 2D or 3D structure can be assumed without a significant increase in computational time. One dimensional models have the advantage of yielding results that are easier to interpret in terms of phases and also they require only one set of simulations for all considered horizontal source and site locations. In addition, the method introduced by Douglas et al. (2004) for the incorporation of the effect of crustal structure into empirical ground motion estimation equations is only practical for one-dimensional structures. The purpose of this article is to investigate when two-dimensional structures provide significantly different results than using an average one-dimensional model. The difference between the 2D and the derived 1D structure is quantified by a single parameter that seeks to characterise how twodimensional the structure is. The maximum size this parameter can be before a 2D structure is required for accurate modelling of ground motions is assessed based on a series of FDM simulations. The purpose of this proposed technique is to provide guidance as to when 2D structures should be used or when 1D structures are sufficient, without the requirement to performing many simulations.