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One of the most important challenges in seismic evaluation of structures comes from wide variability of possible motions that a specific site may experience. This variability arises from the intrinsic randomness of seismic motions (aleatory uncertainty) and lack of knowledge about the physical process behind an earthquake (epistemic uncertainty). The epistemic uncertainty in estimating ground motion can be properly characterized by providing an understanding of the physical aspects of earthquake source models. In this paper, a combination of the theoretical-based Green's function method and hybrid slip source model is used to reduce the source uncertainty. The procedure is implemented on the 1994 Northridge earthquake as a case study. For this purpose, the method is validated against recordings stations through demonstrating a good agreement between the elastic response spectra corresponding to the simulated and recorded data, confirming the reliability of the procedure. A simple additive weighting algorithm is used to select the best fit amongst simulated waveforms and optimal source model. [ABSTRACT FROM AUTHOR]

Pulse-like near-fault ground motions, which are characterized by the presence of a velocity pulse, can impose large demands in structures, and hence can potentially increase seismic collapse risk. One of the most important parameters affecting the structural demands under near-fault ground motions is the pulse period. The commonly used scalar intensity measure (IM), spectral acceleration at the fundamental period of the structure, Sa(T1) is demonstrated to be deficient, and also insufficient with respect to the pulse period, for predicting the structural collapse capacity under pulse-like ground motions. Furthermore, it is shown that the recently proposed IM, named INP, is not able to fully account for the effect of the pulse period. This study proposes an optimal integral-based IM, named ISa, for reliable seismic collapse assessment of structures subjected to pulse-like near-fault ground motions. ISa is the integral of the pseudo acceleration response spectrum over an optimal period range that is a function of the fundamental period and ductility of the structure. To propose the new IM, 15 generic frame structures with different fundamental periods and ductility classes were employed. The results indicate that ISa is significantly efficient, which causes reduction in the dispersion of structural collapse capacity, and also sufficient with respect to the pulse period and other ground motion characteristics for seismic collapse capacity assessment. [ABSTRACT FROM AUTHOR]

Reliable use of b-value in log [N (M)] = a -- bM is critical in seismicity comparisons, seismic hazard analysis, prediction and comparative mechanism studies. Since earthquakes and the b-value are considered as stochastic processes and random variable, respectively, applying the probability distribution of b-value is necessary in its temporal and spatial variations assessment. In this paper, we propose a novel method that employs the b-value uncertainty in probabilistic seismic hazard analysis using normal-exponential joint distribution function. To this end, we calculate b-value statistics based on bootstrap sampling of the seismic catalog. Our analytical and experimental evaluations show that the proposed joint distribution results in a more precise closed-form relation for the probabilistic seismic hazard analysis accurately reducing the hazard in comparison to conventional methods. The benefit of the proposed approach here is improving the ability of assessing the effectiveness of various seismic risk mitigation strategies and so, allocates the available resources more efficiently. [ABSTRACT FROM AUTHOR]

Recurrence models apply historical seismicity information to seismic hazard analysis. These models that play an important role in the obtained hazard curve are determined by their parameters. Recurrence parameters estimation has some features that lie in missing-data problems category. Thus, the observed data cannot be used directly to estimate model parameters. Furthermore discussion about results reliability and probable conservatism is impossible. The present study aims at offering an approach for Gutenberg-Richter parameters (a and b-values) estimation and determine their variation. Applying the proposed method to analyses of the heterogeneous data sets of seismic catalog, one would calculate valid estimates for recurrence parameters. This method has the capability to reflect all known sources of variability. The results of the case study clearly demonstrate applicability and efficiency of the proposed method, which can easily be implemented not only in advanced but also in practical seismic hazard analyses. [ABSTRACT FROM AUTHOR]

This study is intended to investigate the contribution of fling step to seismic demands of the selected structures. Due to the scarcity of real data recorded at the two sides of the causative fault including fling step effects, Fandoqa scenario (Iran, 1998) is simulated using a theoretical Green's function. The three components of the seismograms at Sirch station are simulated using the developed Multi-Objective Particle Swarm Optimization algorithm (MO-PSO) algorithm. The model is calibrated by incorporating the obtained optimal model parameters. The seismograms at four stations close to and located both sides and the causative fault are generated and used as the input data. The fling step contributions are removed from the synthetic data thus providing the seismograms without fling effects. Two structures, a 3D-30 story steel structure dual system (MRF and X-brace) and a 2D-20 story special R/C frame are selected. These two structures are dynamically analyzed under synthetic waveforms with and without fling step contributions. The nonlinear seismic demands over the height of the selected structures with and without fling step contribution are calculated and assessed. It is concluded that in general, fling step may increase or decrease the seismic demands and is not a predictable problem. [ABSTRACT FROM AUTHOR]

In this article a methodology is presented to simulate the three components of seismograms, at low frequency (0-1.5 Hz). This method takes into account three characteristics of observed earthquake such as the frequency content, elastic response spectra and Arias Intensity at near source regime. A multi-taper method is employed for simulating seismogram aimed at accounting for the frequency content. The differences between response spectra, power spectral density and Arias Intensity corresponding to the recorded and simulated data are minimized through an optimization-based inversion solution technique. The proposed methodology is implemented to the 2003Bam scenario (Iran) as an example. The substantial large variance of Fourier spectral amplitudes corresponding to the two sets of seismograms as a main cause of time cost is discussed. Relatively good agreements between the synthetic and those of the predicted waveforms confirm the reliability of the proposed technique in modeling forward directivity effects at near source regime. [ABSTRACT FROM AUTHOR]