Journal of Seismology and Earthquake Engineering
Volume:25 Issue: 1, Winter and Spring 2023

Precursors as informer pioneers of near future occurrence of earthquakes, are very diverse in their natures. We examined three short term possible precursors contain foreshocks, b-value variations, and amplitude abnormalities in the Very Low Frequency (VLF) radio signals for the November 14, 2021 Fin double-earthquakes (M > 6). By searching-zoom method in earthquakes one degree on each side of the hypocenter location in the Iranian Seismological Center (IrSC), the International Earthquake Engineering and Seismology (IIEES) and the Building and Hosing Research Center (BHRC) catalogs, those data for the reviewing foreshocks were provided, then they analyzed by use of ZMAP for the b-value changes based on the Guttenberg-Richter empirical relation methodology. Whereas, in the BHRC accelerometer portal reported 8 events before the main shock times, none of them are not in the other catalogs. The temporal b-value variations from the normal, shown non sharp fits to the rises or falls of the seismicity as an expected indicator. Some b-value in accordance with the seismic up and down rate tracks, have high spatial uncertainties. We observed some amplitude anomalies in the VLF received signals from mean standard deviation in VLF signal measurements (2σ criterion in the statistical method) in about 4 days before and up to 5 days after the main shocks. Albeit, in follow the null hypothesis, for verifying (and not refused) these relations, are needed to be qualified data. As you will see, all three catalogs used in the coverage, quality, verification and appropriate data for logical and reliable review and processing are not less error than the expected standards. The main goal has been to investigate the possible precursors before the 2021 Fin doublet earthquakes by using available local ground base data and obtainable facilities in this field and considering their improvement. The possibility of some foreshocks associated with double earthquakes cannot be ruled out. Therefore, the reliability of the studied precursors completely dependent to the proper data, that sufficient-precise instruments for their observations and recording are vital requirement. It is possible to use that kind of reliable and high-quality data in the analysis of pre-earthquake signals or even reasonable forecasting, which, if possible, will bring a valuable achievement in the future. We came to the conclusion that with such researches, the necessity of data quality and improving the level of their acquisition/standard in the country's research centers, must be carefully defined for more scientific and practical effects.

This study provides a comprehensive probabilistic seismic hazard assessment for Karaj, the capital of Alborz province. In the present study, two probabilistic approaches including the classical and Monte Carlo methods are applied. In this regard, the most recent earthquake catalog of the region, as well as, the most appropriate GMPEs based on the statistical tests of the likelihood and the log-likelihood are used. The results indicated that there are differences between the results of two approaches, which is intensified in the longer return periods. This disparity mainly stemmed from the different concept of two methods for incorporating the aleatory uncertainty. In classical PSHA, the aleatory uncertainty takes into account using the integration which is truncated at a fixed number of the logarithmic standard deviation. While, in the Monte Carlo simulation approach, the aleatory uncertainty is considered in calculation using random sampling of GMPEs variability. In addition, the ground motion shaking map of the region for the dominant seismic scenarios including the rupture of the North-Tehran and Eshterhard faults are developed. These seismic scenarios have the potential of producing the greatest acceleration; consequently, the most vulnerability. The outcomes of this study can be used for providing urban plan or estimating the probable economic and casualty losses of Karaj.

Structural Control is a new method to enhance the behavior of structures. The performance of these systems to reduce damage and improve the behavior of structures in earthquakes is based on reducing the structural demand and absorb the energy of earthquakes in an additive damping system. Poor performance in earthquakes with a seismic level below the design earthquake is a defect in conventional dampers. Since the dampers are considered for design earthquake, they have the best performance in design base earthquake (DBE) level. However, if the structure is designed for a seismic level below the DBE, the structure couldn't have proper behavior in DBE. This defect in passive dampers is one of the main reasons for using multi-stage dampers that making the structure able to have acceptable behavior in different seismic levels.In this study, friction damper and shape memory alloy were combined to behave in two phases. In the proposed damper (FD-SMA), the SMA wire works in the first phase, and it is combined parallel with the friction part. The two-stage behavior result from a displacement gap that works in series with the friction damper. An essential advantage of the proposed damper compared to other two-phase dampers is that the first fuse remains undamaged in moderate earthquakes because of shape memory alloy super-elasticity and leads to maintaining the structure's performance in future earthquakes without repairs. Also, it is expected that the residual displacement decrease in both stages. The small scale of the proposed FD-SMA damper was fabricated and evaluated in the structural laboratory of IIEES. Also, the behavior was modeled in the Open-sees program.The desired dual-stage performance is achieved in all experimental tests. And as expected, the re-centering property of SMA reduces the residual displacement and minimizes the damage in the first stage.The results obtained from the experiment were matched to the model created in the Opensees software, and a satisfactory adaptation was achieved. If unwanted friction is not considered, the first fuse has an acceptable elastic behavior and remains undamaged. Finally, with the parametric study and modeling of 15 different models of FD-SMA damper, the optimal damper was identified.

These days, an increase in terrorist attacks and advanced techniques for creating small explosive devices using powerful, high-explosive materials are causing massive building collapses, economic losses, and death. Protecting and mitigating the effects of explosions on structures and the people in them have become important to scientists. In this article, the effect of different parameters on the target structure, such as standoff distance, charge weight, and the use of protection systems have been reviewed. It is not economical to design the main parts of the structure so that they can withstand different hazards, therefore the use of different protection systems and materials such as walls, fences, sacrificial claddings, sandwich panels, and FRP, to mitigate the blast pressure and diffracted waves, and the results of their analysis have been discussed. The role of these protection systems is to absorb high kinetic energy in the form of strain energy through deformation. It is sometimes possible to replace these systems with a new one after failure at a lower cost than structures without a protection system. This paper presents an overview for beginner researchers to study the effects of the explosion on the structures and investigate solutions to reduce these harmful effects and protect the structures, and their inhabitants.