مجله علوم و مهندسی زلزله
سال هشتم شماره 2 (پیاپی 27، تابستان 1400)

Rapid estimation of the epicentral distance and magnitude is of fundamental importance for real time earthquake detection and earthquake early warning systems (EEWS). Earthquake magnitude and P-wave amplitude are important parameters for EEWS, yet their dependence on source mechanism, focal depth and epicentral distance (Δ) has not been fully studied. We examined a method to estimate an earthquake’s magnitude and epicentral distance using the initial part of P-wave data (within 3 s) for application in EEWS. The B-Δ method is used to estimate the epicentral distance from a single station data in a short time. In order to quantitatively evaluate the difference in observed seismic waveforms, we used a simple function with the form of y(t) = B.t.exp(-At) and determined A and B in terms of the least-squares method by fitting this function to the initial part of the waveform envelope. logB is inversely proportional to logΔ, where Δ is the epicentral distance. This relation holds true regardless of earthquake magnitude. By using this relation, we can roughly estimate the epicentral distance nearly immediately after the P-wave arrival. Then, we can readily estimate the magnitude from the maximum amplitude observed within a given short time interval after the P-wave arrival by using an empirical magnitude–amplitude relation that includes the epicentral distance as a parameter. B values are calculated on the basis of 76 vertical-component accelerograms of the Alborz region in a magnitude range Mw 4.5-6.2 and epicentral distances less than 100 km. By using this method, we could estimate the epicentral distance and earthquake magnitude by specific relations for this region. We showed the amplitude of the large earthquake increases gradually with time, whereas that of the small earthquake decreases soon after P-wave arrival, which is consistent with the observation by other researchers.This method, as a whole, works well for estimating an earthquake magnitude from a B value and the maximum amplitude observed within a quite short time (e.g., 3 sec) from the P-wave arrival. However, some improvements may be required for near earthquakes and for ill-natured earthquakes for which the fault rupture process is rather complicated, such as the Mosha fault with different segments. One measure that we can take to cope with this difficulty is to estimate the magnitude repeatedly with time as the amplitude increases. The term logB may be replaced with other functions such as log(log B). In order to determine the best functional formula for this term, we need further investigations with more earthquake data covering a larger range of magnitudes, depths, and distances. The other parameter A, may be useful for distinguishing shallow and deep earthquakes and large and small earthquakes. This can be an option for future studies.This method can apply as a new stand-alone seismographic system that detects an earthquake and issues a warning immediately after the arrival of P-wave. The greatest advantage of this method is its accuracy and rapidness.

During an earthquake, the waves created by the fault activity in the bedrock propagate from deep to the ground. If the layers on the bedrock are alluvial, the amplitude and intensity of the waves will increase as the waves pass through them, and what reaches the ground will be completely different from what is created in the bedrock. Earthquake waves change their nature as they pass through the bedrock and enter another environment. In other words, the characteristics of an earthquake, depending on the physical and dynamic characteristics of the site, can be intensified or weakened at certain frequencies. The amount and intensity of the amplification of the waves depends on the characteristics of the alluvial layers and the initial wave. Considering that the structures and facilities on the ground are affected by these waves, the intensification of the waves can have very destructive effects on buildings and structures. Determining the magnitude of earthquake waves requires analytical work in an area, based on the characteristics of soil layers and earthquake characteristics. Arak is the cradle of Iran's industry and many strategic and important industries of the country are located in this region. For this reason, it has increased the rate of migration to this city and, as a result, has increased the population of the city, and in proportion to that, high-rise and important structures have been widely expanded in the city. Therefore, in view of all the above, seismic zoning is considered for use in the design of existing buildings and structures, and most importantly, vital decisions such as urban planning, comprehensive urban planning, and comprehensive urban planning. Although the importance of the effects of topography on the seismic response of the earth's surface has become clear to everyone today, due to the lack of comprehensive studies, most earthquake-resistant design codes as well as most seismic geotechnical microzoning guidelines have been used since then. The agent refused.So far, analytical, experimental, numerical and physical modeling methods have been used to study and solve the seismic response of surface topographic features. According to the collection of valid geotechnical information in Arak city, alluvium modeling has been done in this region and alluvial dynamic analysis studies have been performed as one-dimensional linear equivalents and two-dimensional ones using numerical methods and the results have been compared with each other.Considering the changes in the natural frequency of the soil in the studied directions, it can be concluded that in stations with natural frequency of the site less, the thickness of the sediments is slightly higher or the softness of the sediments is slightly higher or the floor rock is slightly lower (at greater depths) than the stations that have a higher natural frequency, Also, by observing the graphs obtained in the northwest-southeast direction, the natural period resulting from one-dimensional dynamic analysis differs by a maximum of 25% compared to two-dimensional analysis, which may be due to the "effect of considering topography in two-dimensional analysis. This is while in the northeast-southwest direction, the results are relatively consistent with each other, which shows the one-dimensional behavior of the site in this direction. Also, in terms of "classification" of soil type based on the shear wave velocity of the upper 30 meters, according to Regulation 2800, soil type has been reported in Arak.

The environment is constantly exposed to various pollutants. Petroleum products may contaminate soils located next to industrial areas and other facilities. Oil pollution is one of the pollutions that can cause irreparable damage to the environment. Every day, a large amount of petroleum products enters the environment in various ways. Oil pollution affects the mechanical, chemical and dynamic properties of the soil. Changing the geotechnical properties of the soil is an important issue for structures adjacent to or on oil contaminated soil that can cause collapsing or variation in soil resistance. Since the behavior of many structures and foundations during dynamic loads is in the range of small strains, investigating and evaluating the velocity of waves in the soil skeleton can provide researchers and engineers with useful and significant information about the small-strain behavior of the soil. The importance and value of oil industry structures in Iran, as one of the active countries among oil exporting countries and as a country with a high level of seismicity, has made the research a vital way to improve the design level and accuracy of the behavior of structures exposed to pollution. Despite the wide range of oil industry structures in Iran and the other countries, there is limited literatures on oil-contaminated soil behaviors. Heretofore, the effects of diverse kinds of hydrocarbon contaminants on majority of geotechnical properties of clay soils such as grain size, hydraulic conductivity, plasticity, compressibility, internal friction, cohesion, and shear strength have been investigated. However, there has not been a concentrated research study examining shear wave velocity of hydrocarbon-contaminated clay soils as an important geotechnical property of soil due to the fact that, in small/very small strain levels, the maximum shear modulus of soils can be determined using shear wave velocity. This study aimed to measure the shear wave velocity and consequently, identify the shear modulus of clay soils in oil-contaminated condition with different percentages of contamination, and to compare them with non-oil-contaminated clay soils on small-strain range, using a Bender Element system. In order to prepare comparable clean and contaminated samples (containing 2, 4, 6, 8, 10 and 12 weight percent (wt%) of crude oil, respectively), it was performed similar to the density test method. In this regard, all the clean and contaminated clay samples were tested with a minimum moisture content equal to the optimal moisture content. Bender element tests were conducted on the identically prepared clean and contaminated clay samples at various amounts of frequency (5–20 kHz) and under various confining pressure (50–500 kPa) to find the best method for accurately determining shear wave travel time in the Bender Elements tests. Thereafter, Bender Elements placed in triaxial cell in Razi university laboratory. Bender Elements test conducted to examine shear wave velocity in the clean and contaminated specimens. As a contribution to the literature and potential engineering application, the experimental test results indicated that whilst adding 10wt% of crude oil in clay samples with an increase in the confining pressure, it correspondingly increase the shear wave velocity and consequently increase the shear modulus among of all samples. In addition, at each level of confining pressure, the shear modulus of clean clay was lower than the other contaminated samples. Moreover, under all confining pressures and excitation frequencies, the addition of 10wt% of crude oil caused significant changes in the maximum shear modulus, which was due to the effects of hydrocarbons on the behavior of clay particles. The degree of change due to hydrocarbons is highly dependent on the amount of confining pressure, so that the more the confining pressure is increased; the shear waves velocity an then the shear modulus is increased.

In current modern cities, the use of buried pipelines in the conveying of vital fluids such as water, oil, and gas have become very important. Investigations on the behavior of the buried pipelines after the occurrence of the severe earthquakes have indicated that one of the primary sources of the failures of these kinds of linear structures were due to surface fault rupture. Therefore, if the buried pipelines are designed and implemented correctly, the permanent ground displacement due to the movement of the bedrock fault will not lead to such rupture of the pipes. On this basis, different researchers have concentrated their studies on investigating the interaction of pipe and soil during the permanent ground displacement. Due to the difficulty and cost of laboratory tests on this phenomenon, the number of available experimental data is very few. On the other hand, analytical studies have various limitations and complexities that have made it difficult for engineers to use these methods. In addition, numerical methods used to study the interaction of pipes and faults are mostly prepared for academic environments. These numerical approaches usually need the knowledge of soil or pipe advanced constitutive models and require the familiarity with mathematical parameters necessary for the convergence of the computational efforts.In order to investigate the behavior of buried pipes against faulting displacement, in this paper, a numerical method has been developed by combining finite difference and Newton multivariable techniques. The equilibrium equation of forces in x and y directions along with the equilibrium equation of bending moment for an infinite section of the pipe under the influence of the displaced soil pressure has been obtained first. Then the system of equations for all of the discretized nodes of a pipeline has been solved using the proposed hybrid method. The proposed method simultaneously considers the nonlinear behavior of pipes, soil equivalent springs, and large strains in the beam-spring model. In addition, to more precisely assess the shear factor in the beam behavior, the Timoshenko beam model has been applied to model the pipe.The validity of the proposed method has been performed using the results of a laboratory centrifuge test on HDPE pipe and 90° normal fault. In addition, this hybrid method is also validated with the results of a finite element numerical analysis on 70° normal fault and API5L-X65 oil transfer pipe. Comparison of the obtained results for different parameters such as longitudinal strains, settlement, and flexural bending of the pipes shows that the presented numerical method is very suitable in predicting the interaction behavior of pipes against dip-slip faults. At the same time, a lower computational effort has been required to arrive in the final answers. In addition, using the proposed numerical method, the effect of fault zone width with values equal to 0.001, 10, 30, 60, and 100 m on the behavior of a pipeline against a normal 70-degree fault has been investigated. The results of this study show that increasing the width of the fault zone significantly reduces the amount of tensile strain in the pipes. Also, increasing the width of the fault zone causes the pipe to rupture from two different points, while in the small fault width equal to 0.001 m, the pipe failure occurs only at one point. Maximum bending moment and pipe curvature also increased with decreasing fault width.

Vertical Mass Isolation (VMI) method is used for the seismic control of structures. In this method, the entire structure is a combination of two mass and stiffness subsystems with an isolator layer located in-between. This method mainly uses the principle of periodic shift as a solution to reduce the seismic responses of the structure. In this method, the majority part of the structure mass is concentrated in the mass subsystem. However, this subsystem constitutes a small percentage of the stiffness of the main structure. Unlike the mass subsystem, the stiffness subsystem constitutes a small percentage of structural mass and a large percentage is structural stiffness. This isolation method makes the mass subsystem behave like a soft structure and move away from the resonance zone. The important point is the seismic control of the mass subsystem, which will be supplied by its connection with the stiffness subsystem provided by the interface dampers. The main difference between the VMI method and coupled structures methods is that the main structure is divided into two isolated structures with two completely different behaviors in this method. One of them has a soft behavior and the other has a hard behavior. However in the coupled structure methods, the control of the two main structures is done by each other and observing soft or stiffness behavior in these two structures is not required. A magnetorheological (MR) damper is used as the isolator layer to control the structure. The model used for these dampers is based on the modified Bouc-Wen model proposed by Spencer et al. in 1997. The clipped-optimal procedure that is one of the most beneficial algorithms is applied to control the MR damper. Passive-off and semi-active control techniques are applied to control the MR damper based on the applied controlling voltage. The maximum voltage that is applied to the MR damper, is equal to 9 V. A third control technique named Copt, which is based on the optimal damping, is used to compare with MR damper results. To evaluate the performance of the proposed control system, a wide range of structures with low to high floors are considered. To do this, structures with heights equal to 27, 54, 108 and 162 meters were selected. Using approximate fundamental period based on ASCE-7, the periods of structures are 0.5, 1.0, 2.0 and 3.0 seconds, respectively. Since all models are SDOF and linear elastic analysis is applied, the structural mass is considered equal for all models (M=100 ton), but the stiffness of models is calculated based on their mass and periods. The damping ratio for non-isolated structure is considered to be 0.05. The results indicate the proper performance of the semi-active method in reducing the responses of the isolated structures compared to the non-isolated structures. This method decreases, on average, the top floor displacement of mass-subsystem by 6%. However, the Copt method decreases it by 21% and the passive-off method increases it by 8%. The semi-active method decreases, on average, the top floor acceleration of mass-subsystem by 13% and 50%, less than the Copt and the passive-off methods, respectively. The findings demonstrated that the semi-active control method based on a maximum voltage of 9 V will reduce, on average, the maximum base shear of isolated structures by 30% compared with non-isolated structures. The parametric approach based on the Nekooei relation (Copt) that is applied as a passive control device had acceptable results for controlling the acceleration and base shear of the structure. This method led to the absolute acceleration of top floor and the base shear of structures to decrease by 53~68% compared to the uncontrolled structure. However, the efficiency of Copt method to reduce the top floor displacement is less than the maximum base shear of the structure.

Using shaking tables in experimental studies on buildings or other installations subjected to earthquake actionsare considered inevitable in many circumstances. Due to their unique abilities in simulating ground motion effectson prototype systems, such facilities can provide the researcher with the most accurate and sophisticated results onthe role of earthquake actions on the specimen under investigation. However, providing accuracy in ground motionsimulation for shaking tables needs careful attention to its subsystems and dynamic interaction between them(specimen, table, actuators, control system and the foundation). In fact there is the possibility of a strong interactionbetween the shaking table itself and the specimen under investigation depending on its weight and frequencycontents. Interaction between the table and its foundation assembly can also be considered important in certaincases. In addition, during shaking tables operation some vibrational force and energy can be transferred to itssurrounding environment and causes undesirable effects in the nearby buildings. In this case, vibration isolation forthe foundation of shaking table can partially solve this problem. However, it may also intensify the interactionbetween the table and its foundation that needs to be addressed properly to maintain the accuracy of the system inground motion simulation. In this work a simplified model for investigation on the role of vibration isolation onfoundation of shaking table assembly is proposed that takes into account the interaction problems among allsubsystems of shaking tables. A large number of time integration analysis subjected to actual earthquake records(applied in the table’s degree of freedom) have been carried out on this model. According to the results of this study,vibration isolation on a 4000 tons foundation of a typical middle size shaking table (6 by 6 meters in size with theweight of 40 tons) reduces, on average, the level of maximum acceleration transferring to the ground to about 1/3of that for the non-isolated system. This has happened in the expenses of about ±3 mm maximum lateraldisplacement for the foundation with respect to the ground. However, the results in this case also signifies sensiblechanges in the actuator’s force, stroke and frequency demands that have to be provided to meet the requiredaccuracy in the ground motion simulation. In addition, according to the results of this study the dominant frequencyof vibration that transfers to the ground and the surrounding environment in case of non-isolated foundation is in therange of 8 to 15 Hertz while in the isolated system a low amplitude dominant frequency exist within the range of 5Hz. Such results vary with the change in the mass and natural frequency of the specimen subsystem. According tothese results vibration isolation for the foundation of shaking table is quite effective in reducing vibrational effectstransferring to the surrounding environment and nearby buildings. On the other hand, using vibration isolationtechnique in design process for foundation of shaking tables may require a major upgrade in the technical specifications for actuators of the table and a need for more sophisticated control system hardware and its add-onalgorithm and software.

Today, the importance of earthquakes in Iran is increasingly understood as the expansion of cities and population concentration in them intensifies. In this regard, the city of Tabriz is one of the settlements that has repeatedly experienced direct exposure to earthquake risk. The earthquake risk zoning of Tabriz, which was carried out by Tehran Padir Company in 2009, has predicted more than 426 thousand human casualties for the earthquake in North Tabriz. The north of Tabriz fault is the most fundamental formation in the area of Tabriz plain, which has been created in terms of its compressive subsidence, Tabriz plain. In addition, since the above fault cuts most of the Quaternary sediments, it has high seismic strength.Studies show that a lot of construction has been done exactly in the study area (District 5 of Tabriz) and completely on the fault and its area (Figure 2). While according to the regulations of urban planning, construction and creating use in cities, it must be at least 20 km away from the fault area. The zoning of tectonic factors (slope and topography) shows that despite the unfavorable geographical conditions in this part of the city and the lack of observance of construction in the fault area in the last century, uncontrolled population has continued with severe erosion of residential structures. However, despite the warnings of researchers and experts and the awareness of relevant officials about the risk and risk of housing construction, especially high-rise housing and commercial towers in the study area, construction and construction activities are still in full swing. The possibility of seismic potential of severe historical earthquakes with the formation of marginal tissues in the last 50 years and consequently the erosion of these tissues in the study area will lead to a major human catastrophe in this city.Analytical-descriptive research method and two sets of compatible and incompatible criteria have been used. Using a multi-objective genetic optimization algorithm, as a new meta-innovative method, a model has been proposed in combination with GIS, which simultaneously selects the population and examines the quality of the location based on the defined objective functions.Suitable locations for temporary housing for earthquake victims are shown in Figure 8 of the Temporary Accommodation Prioritization Map. In general, according to the location of the study area and available data with 14 different natural and human criteria, including the dimensions of safe places, population density, canals, green space, sports, passages, number of floors of buildings, gas transmission lines, training centers, fuel stations, fire stations, medical centers, fault lines and slope, the optimal locations for temporary accommodation of earthquake victims in District 5 of Tabriz were identified. The results of this study show that parts of the city that have sufficient open spaces and at the same time are compatible with the surrounding uses, have a relatively better potential for the location of the injured. In contrast, areas with high population density, relatively high vulnerability, mixed uses and lack of sufficient space and with planning value, have the least possible ability to plan temporary housing for earthquake victims. According to the results of the study, the best places for locating earthquake victims in District 5 of Tabriz, related to open spaces, gardens and barren lands have been evaluated.This study shows that parts of the city that have sufficient open spaces and at the same time are compatible with the surrounding uses, have a relatively better potential for the location of the injured. Moreover, given that genetic algorithms, especially the optimal multi-objective genetic algorithm, are used to optimize the answers obtained.Which have several functions and purposes were used In which it demonstrated its efficiency for the rapid transfer of earthquake victims and the allocation of population blocks by defining target functions commensurate with them, to temporary accommodation, Therefore, this research, with its capability, knowledge and information, was able to do better planning for temporary accommodation of citizens in the time after the earthquake.

In order to estimate the seismic hazard of a specific site, the classification of that site is of particular importance.On the other hand, in order to interpret and analyze the ground motion data in different parts of the world, it isnecessary to know the site conditions in seismic stations. In some countries, including Iran, there is insufficientinformation on the geotechnical and geological status of many seismic stations. The conventional methods tocharacterize the site are based on shear wave velocity measurement such as SCPT measurement, downhole testing,and seismic refraction. These methods have some limitations such as costs, maximum depth, execution problems,etc. This research is a new and efficient approach in site classification using the data recorded from the seismicnetworks, image processing techniques, neural networks and set of 5% damping spectral ratio reference curves ofhorizontal to vertical component (H/V) for the four different site classifications. These reference sets, that includefour separate H/V curves for four different site conditions labelled as rock, dense soil, medium soil and soft soil andclassified as site I, II, III and IV, have been selected from the study of Zhao et al. [1]. The reference curves are basedon K-net seismic network data. The adopted soil classifications are based on Japan Road Associationrecommendations. For the periods of interest, which were not presented in the Zhao et al. [1], the curves wereinterpolated to come up with the values at the missing periods.In this research, two types of basic radial functions (RBF) are called "probabilistic neural network (PNN)" and"general regression neural network (GRNN)", as well as "convolutional neural network (CNN)" have been used. Forneural network input, the data from 182 seismic stations have been incorporated. The site condition at the location ofeach station has been fully characterized. The horizontal to vertical spectral ratio for each recorded seismic eventwas calculated. The ratio for each data was smoothed using the moving average function. Then, the smoothed H/Vratio was normalized to match the sigmoid transfer function upper and lower range, which could minimize thenetwork training time. For the CNN network, the input H/V spectral ratio images were first unified using the exactdimension of 150×300 pixels and then compared to the reference H/V spectral ratio using image processingtechniques implemented in MATLAB software.To verify the proposed technique, H/V spectral ratio was calculated for all events recorded at all 182 stations andthen used as input for training the PNN, GRNN and CNN networks and then compared to the reference curvesproposed by Zhao et al. [1]. Two normalization methods were incorporated; in the first method, all the H/V spectralratios normalized to the maximum amplitude, and the second was to normalize the maximum to one and minimumto zero. The results confirmed that the second normalization method could produce more accurate results due to abetter matching the sigmoid function.According to the obtained results incorporating the second method of normalization and all 790 ground motiondata, which were recorded at 182 different stations., the PNN, GRNN and CNN networks have succeeded inaccurately predicting the site conditions in 73%, 71% and 81% of the stations, respectively. The results could provethe applicability of the proposed approach, using neural networks, in site characterization.References1. Zhao, J.X., Irikura, K., Zhang, J., Fukushima, Y., Somerville, P.G., Asano, A., Ohno, Y., Oouchi, T., Takahashi, T. and Ogawa, H. (2006) An Empirical site-classification method for strong-motion stations in japan using H/Vresponse spectral ratio. Bulletin of the Seismological Society of America, 96, 914-25.