BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2018 | Volume:4 | Issue:4 |Papers Count:8

The study area is a part of the Alpine-Himalayan orogen. It is formed by the Greater Caucasus Mts., the Lesser Caucasus Mts., the Talesh Mts., the Kura Basin, and the South Caspian Basin.Present-day structures of the study area are controlled by the ongoing collision of the Arabian and African plates with Eurasia. The study area extends over 1342 km2 located in Northwest of Iran, which can be regarded generally as the continuation of structural grain of Lesser Caucasus. However, the existence of rigid block of South Caspian Basin and the different lithology of Azerbaijan including Quaternary volcanic masses such as Sahand and Sabalan has resulted in a complex distribution of deformation in the studied area.Northwest Iran is a region of vigorous inflection, deformation and seismicity situated between two thrust belts namely Lesser Caucasus to the north and the Zagros thrust belt to the south.What is known about Seism tectonics of the area located in north of Tabriz fault is limited to the recent works done by Masson et al. (2006). Using dense GPS, they determined that the deformation in NW Iran is characterized by ~8 mm/yr of right-lateral movement on the North Tabriz fault, and ~8 mm/yr of extension within Talesh Mnt. The duplicate Ahar-Varzeghan earthquake focal mechanisms contradicted the GPS results. Although both main shocks have probable fault planes that strike roughly east–west, it is likely that the mapped surface faulting should be associated with the first main shock because field observations record nearly pure strike-slip motion that would be inconsistent with the transpressional mechanism of the second main shock (Ghods et al., 2015).The fault study of Coopley et al. (2013) introduced three Segments with a length of 400 m. till 8 km. In 2012 August 11 (12: 23 UTC), a moderate earthquake with MW=6.4 (USGS) occurred between Ahar and Varzeghan towns in Azerbaijan Province at northwest of Iran, in a region where there was no major mapped fault or any well-documented historical seismicity. In order to solve this problem, Ghods et al. (2015) have introduced a model to resolve this earthquake focal mechanisms and many active fault earthquake rupture in the range of Ahar - Varzeghan.A combined study of active tectonic parameters such as geomorphic indices and stress tensor measurement, allowed to recognize a new fault in the northern part of North Tabriz Fault. In addition to the seismicity of North Tabriz fault, seismicity map of Azerbaijan shows the same distribution ratio in the NW part of the North Tabriz fault. In the absence of active faults, the relation of this seismicity is not known. This study was an attempt to introduce one of the active faults at the North of the North Tabriz fault in order to improve the understanding of seismotectonic characteristic of this area.In order to inquire the relevance between rock rigidity and SL index based on a simplified geological map of the area and field observation, rocks were categorized by their resistance as below: Very low (young alluvial deposits), Low (old alluvial deposits, poorly consolidated conglomerates, marl), moderate (gypsum, gypseous marl), High (limestone, sandstone, dolomite, shale, conglomerate, tuff, schist, flysch sediments), Very high (andesites, trakiandesite, gabbro, dacite) (El Hamdouni et al., 2007).Based on the mentioned category, the distribution map of lithological resistance was obtained using GIS. To assess tectonic activities in the area, geomorphic indices such as: the stream length- gradient index (SL) and hypsometric integral (Hi) have been used to reveal vertical active movements along a particular fault, namely Nahand fault. This fault lying in north of Tabriz fault strikes parallel to it with a length of 168 Km. The combination of morphometric studies and kinematic study show clear vertical movement along Nahand fault. Determination of stress tensor and geomorphic indices has shown that the Nahand fault is a right-lateral strike-slip with a minor vertical component. Field observations and the inversions of stress tensor (geologic and seismologic fault kinematics) revealed that the Nahand fault is an active fault, acting in a transpressional tectonic regime, with the Sh-max oriented NW-SE.

With increasing the earthquake records over the past decades, it has been determined that ground motions in the vicinity of the causative fault (up to 15 km from the fault) can be significantly different from the motions away from the fault. These movements often include high displacement and velocity pulses with a significant structural damage potential and impose considerable seismic demand on the structure. Due to the devastating effects of such earthquakes, many engineers and seismologists have focused on the quantitative identification of pulse bearing records and simulation of the near-fault ground motions.Many simulation models extract the prevalent velocity pulse of the near-fault motions through fitting the displacement, velocity, acceleration time histories, and the corresponding elastic-response spectra obtained from the model and the actual record. So far, determination of the analytical models parameters has been accompanied by a manual trial and error process. Such trial-and-error-based process limits the ability of engineers to apply these relationships and investigate their effects on research and practical applications. In this study, a new approach is proposed for identifying and extracting the prevalent velocity pulse from earthquake records by optimization algorithms and the mentioned models. Particle Swarm Optimization (PSO) algorithm is used to simultaneously minimize the difference between the time history and the corresponding elastic-response spectra of the simulation model and those of actual, by defining a suitable objective function.The objective function in the optimization process is as a constrained function where the root-mean-square difference between the values of the pseudo-velocity elastic-response spectrum obtained from the pulse simulation model and its actual record is as the target function, and the root-mean-square difference between time histories of the corresponding velocity is as the constraint. With the objective function defined, the physical parameters of the simulation models are determined without the need for manual trial and error process. The optimization algorithm converts the manual trial and error in process of pulse extraction into the systematic trial and errors with the minimum analytic intervention and judgment. Then, by the proposed method and Hosseini Vaez mathematical model, a set of near-fault records have been simulated and stated in mathematical expression. The mentioned model includes harmonic and polynomial expressions, which is capable to simulate various pulses with a simpler form. Although this model simulates the long-period portion of near fault records, the parameters of model are determined based on a try and error method. The proposed method has been used to extract and simulate the prevalent pulses of near-fault records of Iran for the Tabas and Bam earthquakes.Comparing the results with other studies represents the efficiency of the proposed method for extracting the prevalent velocity pulse from near-fault records and expressing them as closed mathematical equations. The generated pulse history can be used to structural analysis and investigation of structures response to near-fault ground motions. Besides, since the synthetic near-fault ground motions are a combination of long-period-dependent velocity pulse and high-frequency independent seismic wave, the proposed approach can be used to generate time history of the long-period dependent velocity pulse.

Since the last two decades, the inversion of fault kinematics combined with geodetic and geophysical data has led to the better understanding of the geodynamics of the Arabia- Eurasia collision, as well as the tectonic history of Iran. These researches indicate that dynamics of ongoing deformation in the most parts of the Iranian plateau and surrounding deformation belts is controlled by the NNE- to NE-trending Arabia – Eurasia convergence. This general pattern of deformation has been affected by local- and regional-scale geodynamic elements (e.g., the rigid South Caspian Basin, Persian and Anatolian extruding blocks) producing complex stress and strain fields in distinct tectonic zones such as northwestern Iran and the region surrounding the South Caspian Basin.Accordingly, two drastically different stress fields prevail in either sides of the North Tabriz fault such that the NW-trending horizontal compression in the northern part changes into the NE direction in the southern regions; the type and boundary of this change remain unknown. Every kinematic and structural investigation in NW Iran would help to determine the boundary condition and characteristics of this significant geodynamic complexity. The Mahneshan–Mianeh Cenozoic basin, located at the transition of the two aforementioned tectonic provinces, is a key area providing crucial data for this geodynamic issue. This area, which is also called “Folded Miocene Belt”, is a NW-trending fault-bounded narrow basin developed in the hinterland of the NW-trending Zagros orogen. The Late Miocene detritic sedimentary sequence of the Upper Red Formation constitutes the dominant outcrops of the basin. The sequence is unconformably overlaid by Late Miocene conglomerate to Pliocene-Quaternary deposits. Main geological structures of the basin are NW-trending detachment folds evolved in the fault-related folds in hanging wall of shallow reverse faults. This structural assemblage has been produced and evolved by different stress states during the Late-Miocene compressional tectonic regime.The original data presented in this paper are based on the remote-sensing analysis of satellite imageries and structural field surveys including the study of folding stages, folding interference patterns and faulting trends. These are complemented by the measurement of folds geometry and fault kinematics data collected in 25 sites throughout the area of interest. The inversion of fault kinematics data allowed us to investigate the post-Miocene tectonic regimes affecting the area. The sorting and separation of the kinematics data has been done considering relative age relationships of fault planes and their striations (e.g. using cross-cutting and superposition relationships). FCALC software is used for the inversion analysis, with especial attentions to the rules of data separation, rotation and geological considerations recommended in fault inversion processes.The inversion of fault slip data related to the youngest tectonic regime leads to the determination of the present-day state of stress characterized by a NE-trending maximum horizontal compression. The penultimate Pliocene- Quaternary state of stress (paleostress field) was investigated after the removing of kinematic signatures of the youngest tectonic regime. The Pliocene – Quaternary paleostress state is characterized by a compressional tectonic regime with ~N138E direction of maximum horizontal compression, which is compatible with the results of previous researches in surrounding areas.The study of surface folding patterns and geometry of folds indicates superposition of the Late-Miocene NW-trending fold set by a younger sub-vertical NE-trending fold set. This second folding stage is especially developed in northern and central parts of the basin, in Pliocene- Quaternary geological units. Superposition of these folding geometries results in the formation of basin and dome and boomerang interference patterns, which are clearly visible in satellite imageries. The penultimate Pliocene -Quaternary stress field (NW-trending compression) is responsible for the formation of the last NE-trending folding stage. This paleostress field was changed into a modern compressional stress state characterized by a NE-trending regional compression. The modern stress state of the Mahneshan- Mianeh basin is well consistent with the overall direction of the Arabia -Eurasia convergence and clearly discriminates the ongoing kinematic characteristics of the area of interest from the region to the north of the North Tabriz fault. This puts the boundary of these distinct tectonic domains to the vicinity of the North Tabriz fault.

Dams are infrastructures that have an important role in energy and water supply. Any damage or failure of these superstructures can lead to irreparable losses; therefore, the seismic behavior evaluation of dams under strong ground motions is important. This study aims at studying the effects of earthquakes parameters changes in the performance of concrete arch dams, considering different seismic conditions. The well-known analysis approaches such as nonlinear dynamic analysis is used. Various recorded time histories with different characteristics are considered for the analysis process. Besides, different duration definitions are applied on the selected time histories. Another goal of this paper is to find signals with similar energy characteristics as the main recorded time-histories, in order to reduce the computational volume and analysis time. By considering the special energy distribution of the near-fault records, the approach is properly acts on these types of records. The Morrow point concrete arch dam is considered as the case study, which is modeled in the Solid Work software. The Nonlinear dynamic analysis of this dam, considering the dam-reservoir-foundation interaction is conducted in Abaqus finite element software. The concrete damage plasticity is applied to model the nonlinear behavior of the concrete material of the dam body. To survey the effect of earthquake energy distribution on the seismic behavior of the dam, the selected earthquake records have been decomposed to several components with different energy levels, using discrete wavelet transform. The wavelet transform can decompose the earthquake records into components with specific frequency band. Each of these components has an energy value that is a percentage of the whole energy value of the original record. The seismic behavior of the dam under the main selected earthquake records and their components has been investigated. The results indicate that a wavelet component can be extracted from a near-fault record with a lower effective duration (about 60 to 70 percent of the main record) and similar response in comparison to the original record. Moreover, study of the arias intensity and displacement time history of the dam crest shows that the peak displacement in the dam crest occurs simultaneously with the sudden increase in the arias intensity. As this parameter can be a representative of the time history energy value and its intensity per time unit, the above-mentioned results show the effects of time history energy value and its intensity on the response of the dam body. In addition, it is shown that any changes in the time at which the effective component of the earthquake time history acts can affect the response of the dam. This effect depends on the epicentral distance of the station of the recorded time histories. The results of this study can be used for the recorded time histories at the stations near the epicenter. It is obvious that more studies should be conducted to investigate the effects of increasing the epicentral distance on the dam behavior.

Ports are very important nodes of national and international transportation networks and play a crucial role in economic activity of the nations. It is widely acknowledged that the port facilities should be designed carefully to tolerate against the strong earthquakes. On the other hand, uncertainty of structural and geotechnical parameters has a significant impact on seismic performance of the marine systems. In most engineering practices, however, this impact is ignored and the designers prefer to estimate and employ some representative parameters. Therefore, realistic estimation of seismic performance of port structures requires a probabilistic approach based on appropriate involvement of soil and ground motion variability.In this study, the caisson-type quay wall of Rokko Island is considered for the numerical analyses. The foundation and the backfill soils of this well-documented quay wall were liquefied during the Kobe 1995 earthquake, as resulted in approximately 4 m seaward displacement. It settled about 1 m to 2 m and tilted about 4 degrees outward. For nonlinear dynamic analyses in FLAC 2D, the UBCSAND constitutive model was employed in order to account for liquefaction of backfill and foundation soil. Soil is variable in the nature and its geotechnical parameters are rarely constant in spatial directions. Since the parameters of the employed constitutive model (UBCSAND) were totally correlated to the corrected standard penetration resistance (N1, 60), there would be an excellent chance to generate numerous series of random field data through the interpolation of the available boring log data around the quay wall. The covariance of these random data was considered 45% and the mean values were extracted from the interpolation results of the available boreholes. Subsequently, nonlinear dynamic analyses were carried out by the generated random field data. Numerical modeling based on the deterministic parameters resulted in horizontal and vertical displacements of 4.7 m and 1.9 m, respectively. By applying uncertainty of the standard penetration test parameter in nonlinear dynamic analyses, the resulted quay wall displacements vary in the ranges of 4.7-5.7 m and 1.2-1.8 m, respectively, in the horizontal and vertical directions. These impressive changes indicate that the involvement of spatial variability of soil parameter has significant effects on the assessment of permanent displacement in the quay wall systems. This paper presents a reliable and simple method for consideration of spatial variability of standard penetration test results in dynamic analysis of gravity quay walls. The resulting numerical displacements can be employed for probabilistic seismic design of the quay wall.

Experiencing earthquakes with different magnitude scales every few years, Iran is one of the most seismically active countries in the world.Therefore, it is very important to do research studies in terms of seismology before construction of bridges.Without considering seismic parameters, it would not be possible to design earthquake resistant bridges. Earth`s natural structure in different areas varies in relation with factors including kinetic energy at faults, global plate movements, velocity and maximum acceleration of plate displacements as well as the frequency and oscillation time.As mentioned before, demolition of an important structure like bridges, which is one of the basic elements in communication system among different areas leads to both heavy losses of life, and economic, social, hygienic and political losses. While a close and exact searching look at real seismic conditions of design site makes engineers able not only to prevent heavy costs of design and construction of bridges and to decrease earthquake losses significantly, but also to hold the communication system in service for the purpose of providing passages for firefighters to make all losses minimum.Studying occurred earthquakes such as Northridge and Kobe, which caused a lot of losses to different structures especially bridges contribute to feel the need of considering and studying available bridges in Iran under earthquake.According to the increasing growth of studies in field of vulnerability assessment and earthquake-resistant construction, this need was felt that a damper tested in building structures would be used as an option to make bridges earthquake-resistant.In this article, analytical studies have been done on an available concrete bridge, which is common in Iran based on structure types and its elements arrangement.This bridge was modeled in SAP 2000, and the model was run based on four earthquake records including Tabas, Kobe, Northridge and El Centro applying four different PGAs and nonlinear dynamic time-history analysis were carried out, then the steel accordion damper was installed in order to compare analysis results of model before and after the damper installation.The result showed a decrease in seismic response of bridge structure after damper installation and acceptable amount of energy absorption and losses by dampers, which contribute to energy-loss increment in different elements of the main structure. These results lead to the conclusion that steel accordion dampers are a suitable solution in earthquake-resistant design of bridges.

The purpose of this research is to generate a pulse-like acceleration spectrum from the horizontal component of a non-pulse-like acceleration spectrum. Three different methods have been used for this purpose. Therefore, 63 accelerograms were selected from 450 recorded accelerograms in the near-field and according to the pulse-like and near- fault acceleroram criteria. The geological location of the stations is based on the data published by BHRC (Building and Housing Research Center).Required corrections have been applied in the frequency and time range of the used accelerograms, their values have been scaled to 1 g, and the spectrum of each of the accelerograms is calculated. Computing and modeling of pulse-like coefficients of the accelerograms have been done using three statistical methods as follows: 1) Representing the average for ratios of acceleration spectrum of horizontal components, which are perpendicular along the fault, to the non-pulse-like acceleration spectrum of horizontal components for the same accelerogram, for all of the rock and soil type data, individually.2) Representing the average for the ratios of acceleration spectrum for horizontal components of non-pulse-like accelerograms, which are perpendicular along the fault, to the acceleration spectrum horizontal components of non-pulse-like accelerogram that is recorded in another station.3) The average for the ratio of acceleration spectrum for vertical component, to the acceleration spectrum of the horizontal component perpendicular along the fault, for the same pulse-like accelerogram.Due to the scattering of data and their shortage, especially in sites of groups 3 and 4, the outputs of these two groups are combined and represented as the group of soil, and the outputs recorded in the sites of groups 1 and 2 are also combined and represented as a rock group representative. Then, a comparison was made between the correction coefficients of the obtained spectra and the coefficient N introduced in the 2800 buildings standard in Iran. Errors in each method have been determined and appropriate mathematical models are presented for the 50% balance in each of the three methods. Then, the coefficients obtained from the methods are applied to the non-pulse-like spectrums and are compared with the recorded pulse-like spectrums. The following results have been obtained from these studies: - The proposed mathematical models for modification of the design spectrum in each of the methods have a fairly high accuracy and reliability; however, these methods have considerable differences compared to the Iran's 2800 standard of buildings.-The basis and criterion for obtaining the N coefficient in Iran's 2800 standard is not known, whereas by applying this coefficient it can be said that the effects of the near-field have been applied. It is suggested that this issue is addressed in revision of Iran's 2800 standard.-The natural period of the structures designed by the regulations (short and medium order construction structures) is usually less than 2 seconds. In this interval, the proposed coefficient of the regulations and the proposed coefficient models presented in this study have the largest differences in relation to each other.-The N coefficient always increases after a period of 0.5 seconds for up to 4 seconds, after which it remains constant, which is very conservative and irrational. While in the first and second methods suggested in this study, the slope of the curve is descending from a certain periodic range.This part confirms the justification of the applied procedures too.-Error values are presented separately for each method. In the model provided for the soil, the error value is slightly higher than the rock model.-The magnitude of the error is mostly positive in many periods, which means that the domains of the proposed models of the N coefficient are less.-The absolute and relative errors in the first method are about 0.33 and 5%, and for the second method, it is equal to 0.05% and 15% respectively.-Among the results of the three methods carried out at 50% level, the first and second methods have a much better and more reliable consistency than the third method, and also compared to the 2800 standard.-As one of the most important results of this research, it can be stated that the results of the third method presented in these studies has no logical connection with the pulse-like accelerograms to be used to understand the N coefficient.-According to the comparisons, from the first and second methods, the results of the first method are found more countable. The reason for this is the insignificant difference between the pulse-like modeled spectrum by the application of this coefficient (N) in the proposed model and the pulse-like spectrum of the real records obtained from the earthquakes.

The composite RCS moment resisting frame, including concrete columns and steel beams, has some advantages in comparison with the ordinary steel and concrete moment resisting frames. Previous studies have shown that these systems, in case of preserving sufficient strength and needed ductility in seismic condition, could be effective in design and construction. Notwithstanding the previous research, during the 1970s and 1980s, the use of this composite structural system was limited to areas with low seismic hazard in the US, and it was used as a replacement for steel moment resisting frames and high rise buildings. Besides, in Japan, it was used instead of concrete frames in low rise and short span buildings. In the previous research on these structures, studies were made on the frame and RCS connections, but there has not been any study on the seismic assessment of the RCS structure with time history and for the near-fault earthquakes. Investigating the structure behavior under near-fault earthquake, due to the special nature and characteristics of these earthquakes in comparison to the far-fault earthquakes, seems to be essential. In this research, the seismic demand of composite RCS and concrete structures under the near-fault earthquakes are investigated in comparison with the far-fault earthquakes.For this purpose, five composite RCS intermediate moment resisting frames with 4, 7, 10, 15 and 20 stories and five spans were designed, and then, nonlinear dynamic analysis was performed on the structures using the Open Sees software under 10 far-fault and 10 near-fault accelerographs. The obtained results in this research showed that the stories displacement demand due to the far and near-fault earthquakes in composite structures is lower with respect to the stories displacement of concrete structure due to the same record, and by increasing the number of stories, the values of this difference increase. The effectiveness of near-fault records on the composite structures is greater than the ordinary concrete structures. It seems that the assessment of high rise composite structures with respect to high rise concrete structures yields a better displacement response. Finally, the effect of steel beam in reducing displacement due to both of the records is observed.RESEARCH METHOD: In this research, the seismic demand of RCS and RC moment frames under the near-fault earthquakes are investigated with respect to the far-fault earthquakes. For this purpose, five RCS and RC intermediate moment resisting frames with 4, 7, 10, 15 and 20 stories and five spans were designed and then nonlinear dynamic analysis was performed on the structures using the Open Sees software. Then, 10 far-fault and 10 near-fault accelerographs were used respectively. All used accelerograms that have been received from the site of Peer, had a view to soil type of III on the basis of regulations of seismic design code of Iran (2800) or dirt Class of D based on the classification guidelines of FEMA. To draw the whole reactionary response, the software of SeismoSignal was used and all accelerograms before scaling had their equal maximum with acceleration (PGA). For nonlinear dynamic analysis on intended frames, Open Sees software was used and the results of story displacement, drift angle and story shear were provided in full paper. Selected records in this study were applied to the models and finally the decision has been made among the obtained responses. For scaling, accelerograms used method for scaling of the Fourth Edition of 2800 guideline. Finally, the effect of steel beam in reducing displacement due to both of the records is observed.CONCLUSION: Displacement and drift angle of RC structures under near-fault records was more than far-fault records. However, with increasing the number of stories, drift angle of RC structures under far-fault records was more than near-fault records By an increase in the number of stories, the RCS frames' drift angle due to near records is less than RC frames. The drift angle in RCS tall buildings under near-fault records and in RC tall buildings under far-fault records are more critical. Base shear of RCS structures under near-fault records was more than the base shear under far-fault records and by an increase in number of stories, the difference was reduced. In RCS frames, by an increase in the number of stories, steel beams cause a decrease in effectiveness of drift angle and displacement under near-fault records.