Time history analysis of structures require some carefully selected earthquake records to be employed as the input for dynamic analysis. Despite the increase in number of recorded earthquake ground motions, the need for generation of artificial accelerograms are highly demanded in some areas for some reasons. As a result, many efforts have been made to develop mathematical methods for simulating ground motions by various researchers. Since most of the methods for generation of spectrum compatible signals use relatively complex mathematical approaches, it requires engineers to make more effort and spend time to deal with these complicated methods. In order to meet engineers’ demand for generation of the above-mentioned signals while maintaining an applicable tool that is easy to utilize, a simple, numerically iterative novel procedure has been proposed which is based on linear combination of intrinsic mode functions (IMF) of recorded seismic signals evaluated by empirical mode decomposition (EMD). The proposed method requires only basics of structural dynamics and definitely all engineers are familiar with them and simply can apply the method, while it leads to results as accurate and efficient as benchmark methods such as random vibration theory and time-frequency analysis techniques. The results of this study prove the applicability of the developed approach.

Most of the megacities are located near the active faults. Ground motions in the vicinity of the active faults are associated with two main phenomena so called rupture directivity and fling effects. Therefore, it is important for earthquake resistance design and seismic hazard mitigation to evaluate the characteristics of near-fault ground motions in the megacities. In this paper, the near-fault ground motion was simulated using kinematic model for Tehran City, the capital of Iran. Tehran city was developed along the North Tehran Fault (NTF), which assumed to be the most probable seismic source for the city. Kinematic models are efficient tools to simulate long-period ground motions including slip heterogeneity (Asperities) on the fault and underground geology. Here, the near-fault ground motions are generated assuming NTF scenario using kinematic finite fault model. Then, the variations of faulting parameters such as rise time, maximum slip, rupture velocity, and site to fault distance on the near-fault pulse characteristics are numerically examined and discussed.

Acceleration time histories, recorded during the destructive 26 December 2003 (Mw 6.5) Bam earthquake, have been simulated using the stochastic method for finite faults. In this method, the ground motion amplitudes are simulated as a summation of stochastic point sources. An inhomogeneous slip-distribution model, derived from previous studies is used to asses the source effect. It was found that the overall agreement between simulated and observed waveforms and spectra is well satisfied. The calibrated model is then used to simulate ground motion for the most damaged areas where strong-motion data are not available. This result clearly shows that source effect is capable of explaining the main features of the damage distribution pattern of the 2003 Bam earthquake, especially why eastern part of Bam city suffered the heaviest damage

In recent years, seismologists have attempted to develop quantitative models of the earthquake rupture process with the ultimate goal of predicting strong ground motion. Simulation procedures provide a means of including specific information about the earthquake source, the wave propagation path between the source and the site and local site response in an estimation of ground motion. Simulation procedures also provide a means of estimating the dependence of strong ground motions on variations in specific fault parameters. Several different methods for simulating strong ground motions are available in the literature. A number of possible methods that could be used to generate synthetic records include the following: (i) deterministic methods, (ii) stochastic methods, (iii) empirical Green’s function, (iv) semi-empirical methods, (v) composite source models, and (vi) hybrid methods.The Firozabad Kojoor earthquake occurred on May 18, 2004, with a magnitude of 6.2 in the central Alborz region. We have used the empirical Green’s function and stochastic finite fault modeling to study the source parameters and rupture propagation and make a comparison between the observed and simulated records. The empirical Green’s function method synthesizes the ground motion from a large earthquake (target) by exploiting actual small-event ground motions as the Green’s functions of the earth. It is based on the concept of self-similarity, a notion that assumes a constant stress drop for earthquakes of all magnitudes and provides scaling values for determining related faulting parameters of earthquakes of varying size. The simulation of the ground motion from the target event is expressed as a superposition of contributions from the subfaults separated by a time difference that depends on (1) the location of the particular sub-element on the fault relative to the rupture initiation point and (2) the rupture propagation characteristics. It assumes that the rupture propagates radially from the rupture initiation point at a constant fraction of the shear wave velocity.This study also employs the modified stochastic finite fault modeling of Motazedian and Atkinson (2005), which is based on the dynamic corner frequency. In this method, a large fault is divided into N subfaults, where each subfault is considered as a small point source. The ground motions of subfaults are summed with a proper time delay in the time domain to estimate acceleration time history.The comparison shows that the length and width of the rupture plane is 15×15km. The coordinate of the nucleation point is estimated as 36.33oN, 51.60oE and 29km depth, and rupture was determined to have propagated from east toward the west. The estimated focal mechanism is reverse with a minor left-lateral strike slip component. The strike, dip and rake have been estimated as 110o, 34o and 71o, respectively.

On April 5, 2017, an earthquake with moment magnitude of 6. 1 occurred Sefid-Sang area about 80 km southeast of Mashhad city in Khorasan-e-Razavi province. In this study, to estimate source parameters and rupture characteristics of the earthquake, the Empirical Green Function (EGF) method and the stochastic finite-fault (SFF) technique were used for strong ground motion simulation. Then the observed records and the simulated graphs by these two methods, were compared. To simulate the earthquake by EGF method, an aftershock with moment magnitude of 4. 8 was used as the empirical Green function. The size of the main fault caused by the event was about 10 km in length and 8 km in width. The duration of the rupture in this event was about 18 seconds. The estimated fault plane solution shows reverse mechanism with strike-slip component. Strike, dip and rake of causative fault of the earthquake were determined as 311, 55 and 117 degrees. In addition, the stress drop in this event was calculated to be about 8 bars.

The performance-based earthquake engineering requires reliable assessment of long-period ground motion particularly for tall buildings, base-isolated structures, long bridges, and structures that are designed to deform beyond the elastic range.The important issues involved in such assessments are: Empirical and theoretical tools for prediction of displacement response spectra; Analysis and incorporation of near fault effects; Spectrum scaling for different damping ratios and; Time domain simulation of long-period ground motion. These issues are elaborated through (1) the principles for modification of design basis spectra in the long-period range; (2) guidelines for time domain simulation of long-period ground motions; and (3) rules for selecting and scaling ground motion records to address long-period effects. This paper aims to review and discuss these issues with developments on GMPRs for peak ground displacement and 10s spectral acceleration, and example applications on earthquake hazard assessment for 10s spectral accelerations and its deaggregation in the Marmara Region, Turkey.

Taking advantage of computer technology and science that enable us to carry out a large scale numerical simulation, the authors have been simulating the whole phases of an earthquake, i.e., the generation and propagation of an earthquake, the response and damage of structures, and the human and society actions against the earthquake damages. This is the integrated earthquake simulation (IES). With the aid of the latest geographical information system (GIS), IES is able to automatically construct a compute model for a city of some hundred meter scale. This paper presents the development of IES, focusing the simulation of strong ground motion and structure responses; the structure response simulation is made by several numerical analysis methods and the data exchange between each method and IES is controlled by an interpreter program. Discussions are made on the usefulness of IES. It is pointed out that IES provides vital information to form common recognition of possible earthquake hazards and disasters among government officials and residents.      

Tehran, the capital of Iran, is located in the foothills of Alborz Mountains in a very seismically active region and is surrounded by many active quaternary faults with the potential for devastating earthquakes. This city has a daytime population of 12 million people and is the political and economical capital of Iran as well. These facts together with the existence of neighborhoods with old buildings that are poorly constructed increases the importance of different studies to better characterize the nature of ground shaking from future probable earthquakes in the city. With the increasing computational power in recent years, the seismic waveform simulation has become one of the preferred methods for studying the seismic hazard in regions like Tehran. The topography effect, in this regard, is one of the components of site effects that need to be included in hazard assessment studies. It is a known fact that the surface topography has significant effects on the earthquake ground motion, especially in mountainous areas with ridges and valleys. As has been observed in the annals of past earthquakes and numerical simulations, topography, In general, increases the ground shaking amplitude on mountain tops and reduces the ground motion amplitude in valleys. The Spectral Element Method, combining the power of Pseudo Spectral methods with the geometrical flexibility of Finite Element Method, is one of the best methods for modeling the seismic wave propagation in regions such as Tehran, with notable surface topography. In the present research, the Spectral Element Method was employed in order to simulate three point sources and three extended source earthquake scenarios both within and around Tehran city and to investigate the role of surface topography on the ground shaking inside the city. The topography effect was investigated by comparing the results of simulations with and without incorporating the surface topography in meshes; the resulting amplification was presented as color maps in the region. Simulations were performed via SPECFEM3D software package which implements the Spectral Element Method to simulate the seismic wave propagation in the region. The first step in using the Spectral element Method was to create quality meshes in the study area; in this regard, CUBIT program is employed so as to create the hexahedral meshes in the model area. The extent of the model area was 100 x 60 kilometers horizontally and, vertically, from the ground surface to the depth of 60 kilometers with limits of latitude and longitude of 35. 5 to 36. 5 degrees and 51 to 52 degrees, respectively. The peak ground acceleration amplification maps were presented for the topography effect in the frequency range of 0. 01 to 1 Hz. The findings indicated that the topography effect inside Tehran city is dependent upon the earthquake scenario and the resulting amplification from topography effect inside the city is generally low and negligible. On average, the amplification resulting from the topography inside the city was between-10% to +10% which could reach as high as ± 30% in certain earthquake scenarios at certain locations within the city. In mountainous areas near the city, we observed amplification on the peaks and de-amplification in the valleys; the amplification fell between-50% to +50 %.

According to the IAEA and USNRC (United State Nuclear Regulatory Commision) regulations, calculating a strong ground motion during an earthquake is of great importance for the design of nuclear facilities, especially nuclear power plants. In the absence of precise seismic studies and in case of severe earthquakes, many radioactive contaminants are released into the environment, with irreparable physical and financial losses, hazarding the nuclear facilities, people and the environment. In this research, in order to develop the earthquake attenuation relationships for Boushehr, an important region, simulation of the ground motion was used along with the stochastic finite fault method. The results obtained from the simulation have been compared with the results obtained from the valid world relations for the Zagros region. Evidently, they show good consistency. The proposed model is a theory-empirical relationship of the Bushehr susceptible region, which can be used to assess the safety of the existing nuclear power plant in Boushehr and to design new nuclear power plants in the future.