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Izmir, the third largest city and one of the major economic centers in Turkey, has more than three million residents and one-half million buildings. The city, located in a seismically active region in western Anatolia, was a subject of the 1997 RADIUS (Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disaster) project. In this paper, the seismic hazard of Izmir is investigated through probabilistic seismic hazard assessment. First, the seismic setting of Izmir is presented. Considering the statistics of earthquakes that took place in the region during the period 1900-2005, a simple seismic hazard model is used to facilitate the assessment. To account for modeling uncertainties associated with the values of seismicity parameters, a logic tree procedure is employed in carrying out the seismic hazard computations. The resulting weighted average seismic hazard, presented in terms of peak ground acceleration and associated probability of exceedence, could be considered the 'best estimate' of seismic hazard for Izmir. Accordingly, for a return period of 475 years, for rock sites, a PGA value of 0.34 g is calculated. This PGA hazard estimate is close to the current code-recommended design acceleration level for Izmir. [ABSTRACT FROM AUTHOR]

The recent earthquakes in California and Japan have shown the fundamental role that the road infrastructure plays in emergencies. In fact, only the maintenance of a sufficient level of efficiency can help to quickly reach the affected areas and thus avoid further serious consequences. The necessity of guaranteeing the functionality of the transport network during seismic events therefore requires seismic risk planning extended also to the road infrastructures in order to support the management of post-earthquake emergencies. Analogously it is fundamentally important to have analysis instruments of the road system able to preventatively evaluate the effects of earthquakes in order to identify possible emergencies, therefore preparing a program of intervention to reduce seismic risk on road networks. This paper proposes a methodology for the evaluation of seismic risk of road infrastructures according to the following points:•Study of seismic hazard of the site for the definition of a seismic scenario using attenuation models in relation to historical seismology and the geological and tectonic characteristics of the territory;•Analysis of the direct exposure connected to the probability of the presence of road users on the different parts of the network directly exposed to the seismic event;•Analysis of the indirect exposure relative to the distribution of the population and the infrastructures for which post-earthquake accessibility must be guaranteed;•Evaluation of the functional vulnerability in relation to the potential replaceability of damaged stretches considering network configuration and geometrical characteristics;•Evaluation of structural vulnerability of the stretch correlated to the characteristics (structural, mechanical, technological, etc.) of the different components (bridges, embankments, trenches, tunnels) that make up the stretches obtained by the use of correctly elaborated tables for each component.The determination of global risk indexes of the single stretches and of the network, evaluated by means of a relationship between the ascertained parameters derived from the investigation of the previous points, provides the necessary information for the definition of mitigation measures to reduce the risk and for management planning before and after disaster. The proposed methodology, which has already been applied to a restricted area, is currently being applied to the province of Catania (Sicily, Italy), which is one of the geographical regions of highest seismic risk in Europe, and its future extension to all of eastern Sicily is foreseeable. [ABSTRACT FROM AUTHOR]

To carry out a realistic simulation of earthquake strong ground motion for applied studies, one needs an earthquake fault/source simulator that can integrate most relevant features of observed earthquake ruptures. A procedure of this kind is proposed that creates a broadband kinematic source model. At lower frequencies, the source is described as propagating slip pulse with locally variable velocity. The final slip is assumed to be a two-dimensional (2D) random function. At higher frequencies, radiation from the same running strip is assumed to be random and incoherent in space. The model is discretized in space as a grid of point subsources with certain time histories. At lower frequencies, a realistic shape of source spectrum is generated implicitly by simulated kinematics of slip pulse propagation. At higher frequencies, the original approach is used to generate signals with spectra that plausibly approximate the prescribed smooth far-field source spectrum. This spectrum is set on the basis of the assumedly known regional empirical spectral scaling law, and subsource moment rate time histories are conditioned so as to fit this expected spectrum. For the random function that describes final slip over the fault area, lognormal probability distribution of amplitudes is assumed, on the basis of exploratory analysis of inverted slip distributions. Similarly, random functions that describe local slip rate time histories are assumed to have lognormal distribution of envelope amplitudes. In this way one can effectively emulate expressed 'asperities' of final slip and occasional occurrence of large spikes on near-source accelerograms. A special procedure is proposed to simulate the spatial coherence of high-frequency fault motion. This approach permits the simulation of fault motion plausibly at high spatial resolution, fulfilling the prerequisite for simulation of strong motion in the vicinity of a fault. A particular realization (sample) of a source created in a simulation run depends on several random seeds, and also on a considerable number of parameters. Their values can be selected so as to take into account expected source features; they can also be perturbed to examine the source-related component of uncertainty of strong motion. The proposed approach to earthquake source specification is well adapted to the study of deterministic seismic hazard: it may be used for simulation of individual scenario events, or suites of such events, as well as for analysis of uncertainty for expected ground motion parameters from a particular class of events. Examples are given of application of the proposed approach to strong motion simulations and related uncertainty estimation. [ABSTRACT FROM AUTHOR]

A global seismic hazard assessment was conducted using the probabilistic approach in conjunction with a modified means of evaluating the seismicity parameters. The earthquake occurrence rate function was formulated for area source cells from recent instrumental earthquake catalogs. For the statistical application of the G-R relation of each source cell, the upper- and lower-bound magnitudes were determined from, respectively, historical earthquake data using a Kernel smoothing operator mid detection thresholds of recent catalogs. The seismic hazard at a particular site was obtained by integrating the hazard contribution from influencing cells, and the results were combined with the Poisson distribution to obtain the seismic hazard in terms of the intensity at 10% probability of exceedance for the next 50 years. The seismic hazard maps for three countries, constructed using the same method, agree well with the existing maps obtained by different methods. The method is applicable to both oceanic and continental regions, and for any specific duration of time. It can be used for those regions without detailed geological information or where the relation between existing faults and earthquake occurrence is not clear. [ABSTRACT FROM AUTHOR]