Journal of Seismology and Earthquake Engineering
Volume:18 Issue: 4, Winter 2016

In this paper seismic strain andGutenberg-Richter b-value are used to quantify seismic potential in the Zagros region(Southwest Iran). Seismicity data of the Zagros are extracted from International Seismological Center and Iranian Seismological Center bulletins in timeinterval 1963 to 2015. The b-values are estimated using Kijko-Sellevoll method. The results represent that b-value varies from 0.62 to0.72in the study region.Low b-values (0.62 and 0.72) are accompanied with higher strain rates (1.22×10-8 and 7.46×10-9) in southern parts of the Zagros indicating more frequent large earthquakes. On the other hand, Low b-values (0.64 and 0.72) and lower strain rates (2.39×10-9 and 8.54×10-10) in northern parts of the Zagros indicate less frequent large earthquakes. Recurrence interval of large earthquakes(M>6) is estimated using the b-values and seismic strain rates.Recurrence interval of large earthquakes in southern parts of the Zagros (7 and 8 years) are shorter than northern parts of the Zagros (19 and 45 years).

The Zagros belt in southern Iran is amongst the world's most seismically active mountain ranges that accommodates a significant portion of the convergence between Arabian and Eurasia Plates. Due to the larger earthquakes in Zagros, which have strike-slip focal mechanisms without any coseismic ruptures at the surface; it is important to identify the source of these earthquakes in the basement. The 2005 and 2014 earthquakes with Mw=5-6 in Qeshm Island are examples of them. The NE-trending Gachin fault zone is one of the main transverse faults that cross cut the major structures of Bandar Abbas zone and continues to the Persian Gulf; in which deformations of the fault are overprinted on the major structures. Based on the field, remote sensing and sismotectonic studies; the Gachin fault zone is the main cause of the recent deformations on the Quaternary sediments in Qeshm Island and its activities are continuing to present time; therefore, the above-mentioned earthquakes were caused by this fault. In other words, the convergence between Arabian and Eurasia Plates is in favour for the reactivation of Gachin fault zone in the basement as earthquakes.

Due to the complexity of scattering issues by topographical features above subterranean cavities, few studies have been conducted in this field. In this regard, a 2-D scattering and diffraction of in-plane P and SV waves induced by a U-shaped canyon above underground cavities is proposed herein to account for the topographic effect of such a canyon. To show the interaction between U-shaped canyons and underground cavities or underground holes like natural karstic cavities and their effects on the surface ground motion, a parametric analysis is carried out in the time-domain by BE method. The important parameters considered in this parametric study include: the width of the underground cavities; the cavity depth; the depth and radios of cavity and shape of canyon. The results indicate the following: (1) different incident waves are caused different amplification pattern; (2) the presence of underground cavities may change the surface motion field significantly; (3) the strong ground motion amplitude appears to be very sensitive to the frequency of incoming waves and depends on size and shape of the canyoncavity system, and generally seismic interaction between them.

In this paper, a model of earthquake forecast is presented to assess the long-term probabilities of future earthquakes with moderate magnitudes for a region including Iran (latitude 25-40° and longitude 44-62°). The model estimates a coupled rate of magnitude, space and time for future seismicity using a spatial-temporal Poisson process. The smoothed spatial distribution of seismicity is measured by an adaptive kernel using the locations of past M ³ 4.5 earthquakes listed in the ISC catalog in the period of 1980 to 2014. The retrospective area skill score test has been carried out to check the significant of the results, using a spatially uniform reference model. At 95% confidence level, the model was not rejected by the test. Moreover, the results show a meaningful correlation between anomalies of the forecasted map and the epicenters of target events occurred from 2015 to 2016. Based on the results, it is concluded that the areas characterized by high forecasted rates of seismicity could be considered as the highly hazardous ones, most likely to seismic activation in the Iranian plateau.

This paper presents a methodology to utilize performance-based seismic design procedure for evaluating the effect of heating in lead core of isolated structures with lead-rubber bearing based on collapse assessment and seismic loss estimation. Nonlinear archetypes of conventional 4-story steel special moment resisting frame, isolated intermediate moment resisting frame with and without heating in lead core effect are compared with each other under far-field (FF) and near-field (NF) earthquakes. The results of this study show that heating in lead core increases collapse risk, expected annual loss (EAL) and expected annual fatalities up to 40%. Besides, it has been found that the effect of heating in lead core for isolated structures increases under NF comparing with FF ground motions. Sensitivity analysis is employed to study the effect of modeling uncertainty on the loss estimation process show that the effect of modeling uncertainty on the EAL increases for NF ground motions comparing with FF ground motions.

A new system called Tuned Story Mass Damper (TSMD) is proposed and modified to enhance the seismic performance of mid-rise buildings. In TSMD systems, some part of a story's mass is utilized as Mass Damper, and an external passive damping device is used to provide the expected control force. For an 11-story structural model under seismic excitations, the equations of motion are solved in state space and two objective functions, the maximum displacement and maximum velocity of the top floor are considered to be minimized simultaneously. Using a fast and elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) approach, the optimum design parameters of the TSMD system, including mass, stiffness and damping as well as the best location of the TSMD system among the floors of the structure are obtained. The results show that considering the TSMD system on the fifth floor leads to the most reduction in displacement and velocity, not only for the roof, but also for the other floors as well. For the system under study, comparing with the noncontrolled system, a reduction of about 31% on maximum displacement and 42% on maximum velocity of the top floor are obtained.