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Showing 13 results for Earthquake

Volume 3, Issue 1 (11-2009)

(Paper pages 563-590) This study explores crustal velocity structure in the west of Iran. Wealth of data from recorded local earthquakes creates an opportunity to image crust and upper mantle in the region and then these data use for the joint inversion method in this region. We proposed to study velocity and interface structure of the crust and upper mantle in the west of Iran using local earthquakes recorded in the Kermansha short-period seismic stations at the Institute of Geophysics, University of Tehran (IGUT), and the Sanandaj broad-band seismic station at the International Institute of Earthquake Engineering and Seismology (IIEES), since 2004. The earthquakes and stations should be directed for the travel time curve analysis. Recorded earthquakes were classified along the five separate profiles and 278 earthquakes (mb≥3) separate in data (3000) and epicenter distance is 10-750 km, that corresponding travel-time curves were analyzed. Moreover, crustal velocity structure is determined based on the travel time curve of local event. So, algorithm program was written and arrival times of body waves compare with forward modeling code was written, in order to refine final model. This processing based on earthquakes with mb≥4 and the error RMS is 0.01-0.26 sec. Compressional wave velocity of the crust is 6.23±0.07 km/s and the upper mantel (Moho) is 8.08±0.08 km/s. since, shear waves velocity for the crust, found to be 3.64±0.06 km/s and the upper mantel (Moho) is 4.70±0.01 km/s. Depths for Conrad and Moho discontinuities were obtained 11±2 km and 43±3 km respectively, which well correlate with the results of the previous gravimetric crustal studies
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Volume 6, Issue 1 (11-2012)

Prediction of location of future earthquakes with event probability is useful in reduction of earthquake hazard. Determination of predicted locations has attracted more attention to design, seismic rehabilitation and reliability of structures in these sites. Many theories were proposed in the prediction of time of occurrence of earthquake. There is not a method for prediction time of future earthquakes. Many studies have been done in the prediction of magnitude of earthquakes, but there are not any investigations on prediction of earthquake hazard zonation. In this study, the locations that have probability of the event of future earthquake have been predicted by artificial neural networks in Qum and Semnan. Neural networks used in this study can extract to complicate properties of patterns by receipting the interval patterns. Furthermore, the map of earthquake hazard zonation has been drawn. Properties of occurred earthquake were collected since 1903. The most probable event of earthquake in Qum has been predicted 31.6% in center, and 28.9% in north of Semnan
S. M. Fatemiaghda, V. Bagheri, M Mahdavifar,
Volume 7, Issue 1 (8-2013)

In this research, one of the new methods for seismic landslides hazard zonation (CAMEL) to predict the behavior of these types of landslides have been discussed.  It is also tried to eveluate this method with the proposed Mahdavifar method.  For achieving this result, the influence of  Sarein earthquake (1997), have been selected as a case study. In order to apply seismic hazard zonation, the methodology of Computing with Words (CW), an approach using fuzzy logic systems in which words are used in place of numbers for computing and reasoning is employed. First, the required information which includes disturbance distance, ground strength class, moisture content, shake intensity, slope angle, slope height, soil depth, terrain roughness, and vegetation have been collected using air photos, Landsat Satellite images, geological and topographic maps, and site investigation of the studied region. The data is digitized and weighted using Geological Information System (GIS). At the next step, the hazard rate and areal concentrations with respect to landslide types are calculated using CAMEL program and then, landslides hazard map produced by the above mentioned method is compared with landslides occurred as a result of Sarein earthquake. Finally, for evaluating on prediction of the earthquake-induced landslides, empirical comparison have been done between CAMEL and Mahdavifar methods.
Sm Fatemiaghda, V Bagheri, Mr Mahdavi,
Volume 8, Issue 3 (12-2014)

In the present study, landslides occurred during 1997 Sarein, Iran earthquake are discussed and evaluated. In order to meet the objectives, the Computing with Words (CW), an approach using fuzzy logic systems in which words are used in place of numbers for computing and reasoning is applied. Firstly, the necessary information which include disturbance distance, ground class, moisture, shaking intensity, slope angle, slope height, soil depth, terrain roughness, and land-use have been collected using air photos, LANDSAT satellite images, geological and topographic maps, and site investigation of the studied region. The data is digitized and weighted using ARCGIS software. At the next step, the hazard rate and predicted areal concentrations of landslides with respect to their types are calculated using CAMEL software (Miles & Keefer, 2007). CAMEL provides an integrated framework for modeling all types of earthquake-induced landslides using geographical information system(GIS). Finally, landslides hazard map is compared to landslides triggered by Sarein earthquake.
Arash Shareghi, M Amelmelsak, A Sohrabi Bidar,
Volume 8, Issue 4 (3-2015)

Evaluation of strong ground motion up beneath the construction is important in both geotechnical engineering (site effect) and earthquake engineering aspects (analysis of earth behavior). The common methods of microzonation in geotechnical engineering are based on one dimensional dynamic analysis, in which ground surface is assumed to be horizontal. However in many cases, because of variety of topography conditions, recorded responses are different on the top of hills and their corners. In this study, FLAC 2D software, as finite difference software, is used to analysis the trapezoidal hill with different shape ratios. These topography models are analyzed by far field earthquake records, and their dimensionless amplification ratios are compared with the obtained results of one dimensional analysis. Assessment of these two analyses methods in some points on the topography and around it, demonstrated considerable differences that show the necessity of two dimensional analysis in earthquake geotechnical engineering.
Maryam Rezaei, N. Hasani, A. Khorsandi, A. Rezaei,
Volume 9, Issue 3 (12-2015)

Several studies show that during and before the earthquake, ground water existing in layers of the earth crust undergoes physical and chemical changes. These changes are recorded by measurement devices and known as "Geohydrological Precursors". Based on the studies conducted in this field, earth electromagnetic field waves experience fluctuations during and even before happening of the earthquake, which are called "magnetic anomalies". This type of anomaly is known as "geomagnetic precursor" within the scope of earthquake knowledge. S, the aim of this study is to assess the feasibility of making a connection between two groups of earthquake precursors (hydrological and geomagnetic precursors). In the present research, a series of tests has been done in order to investigate the effect of magnetic fields on physical and chemical properties of water, including Electrical Conductivity (EC), Total dissolved solids (TDS), Height of Water (HW). The tests were designed and conducted to be used in short-term and middle-term earthquake prediction. Analysis of the experimental results using statistical tests indicates that there is a partial meaningful relationship between magnetic fields (geomagnetic precursor) and physical and chemical properties of water (hydrological precursors), with the confidence coefficient equal to 95 percent
Maryam Yazdi, Ali Komak Panah,
Volume 9, Issue 4 (3-2016)

As usage of reinforced soil structures is highly increased in seismic active zones, the analysis of dynamic behavior of these structures begins to be of great significance.  The present paper is an attempt to study the seismic behavior of reinforced soil retaining walls with polymeric strips. The consequences of the most principal parameters counting the length of reinforcement, reinforcement arrangements (zigzag vs. parallel), maximum base input acceleration and wave frequency on the wall displacement have been investigated for sensitivity analyses. The main drawback of numerical methods in dynamic analysis is being very time consuming. Therefore, determination of equivalent coefficients is a suitable, easy and beneficent approach to converge   results of   pseudo-static and dynamic methods. In this case, a relatively accurate design is achieved by using pseudo-static method that takes less time. To this end, an earthquake equivalent horizontal acceleration coefficient is proposed by considering horizontal displacement of the wall as the basis for comparison
M.a Eskandari , P Homami ,
Volume 10, Issue 5 (7-2016)

Most of masonry buildings are vulnerable against earthquakes and need to be rehabilitated. One of the pragmatic methods for strengthening is to utilize shotcreting the masonry walls. In this paper the effects of the soil type (in view of seismic behavior) on the rehabilitation of the masonry building by shotcrete are investigated. Three types of masonry buildings are simulated by ABAQUS software and analyzed against three earthquake records to find their reporses and seismic demands. Using five types of shotcrete configuration consisted of shotcrete strips in vertical and horizontal directions for rehabilitation are studied to find the appropriate method for damage mitigation. The suitable method for rehabilitation are used to study the effects of soil type on the rehabilitated buildings. Three records of the Tabas (1979) earthquake which were recorded on different types of soils (Type I, II and III based on the Iranian seismic design regulations) are considered to analyze the sample masonry building. The results show that the shotcrete method is more effective for buildings which are relying on the softer soils and in stiff soils it is recommended to combine the shotcrete method with other rehabilitation methods which are able to strengthen the building without increasing the stiffness of the building, like utilizing post tensioning cables.

Aida Jahed Shiran, Masood Azhdarifar, Afshin Meshkat-Dini,
Volume 10, Issue 5 (7-2016)

This research is focused on an analytical approach to investigate the seismic performance of tall building under scaled near-field earthquake records. To achieve this objective, it is employs medium to high rise steel bundled-tube rigid frames. The examined structures are designed according to the Iranian seismic code 2800 (4th edition). To study the seismic response, groups of near field earthquake records with their associated properties are selected to perform non-linear time history analyses. The most important characteristic of the chosen near-field earthquake records is the presence of powerful long-term velocity pulses which distinguishes them from far-field earthquake records. The first part of the mentioned ensemble includes two recorded strong ground motions in Iran i.e. Tabas 1978 and Bam 2003, respectively and two powerful records of the Northridge 1994 earthquake. The second part contains one far-field record of the Northridge 1994 earthquake. The selected records are scaled based on the Iranian seismic code 2800 (3rd and 4th editions). The characteristics of seismic performance of each structural model, including maximum relative displacement of each story, seismic base shear and the formation of plastic hinges in the resistant skeleton have been carefully evaluated. The results indicate that using the 4th edition of the Iranian seismic code 2800 produces noticeably lower values of scale factor and their associated seismic responses in the studied structures as well as the nonlinear demand of the main load bearing members under scaled records with those factors, compared to the corresponding analytical cases based on the 3rd edition of the Iranian seismic code 2800. According to the results of this study, the rate of the drift parameter variations of structures that have been evaluated on the basis of seismic code 4th edition in comparison with the seismic code 2800 are experiencing a relative reduction about 30%.
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Volume 12, Issue 1 (8-2018)

 IExtended Abstract
The Iranian plateau is situated in the Alpine-Himalayan orogeny between the Eurasian plate in the north and the Arabian plate in the south. It is being shortened by the northward movement of the Arabian plate, which causes the most parts of Iran to be active and dynamic in terms of tectonic movements. The recent tectonic activity in the southern edge of central Alborz causes both development and deformation of the tectonically active landforms. Seismic records indicate a high frequency of earthquakes of relatively small magnitude (<4) and infrequent large earthquakes (>5.1) in the Alborz. The studied area is located in the southern central Alborz and at the edge of northwestern central Iran between seismic faults of Ipak (with approximately E-W trend) and Avaj (with NW-SE trend) that includes significant earthquakes. Generally, the dominant tectonic structures of the study area involve thrust faults. The Ipak fault is one of the major fault systems in the area, located about 120 km west of Tehran, and caused the 1962 Buin Zahra earthquake of Ms 7.2 (Mw 7.0). The earthquake was associated with 95 km surface rupture along the Ipak reverse fault with average throw of 140 cm and left-lateral displacement of 60 cm. This investigation has evaluated the active tectonics and the acceleration zoning of the region in order to analyze and measure the recent tectonic activities.
Material and methods
To assess the acceleration zoning of this region, seismic data, Kijko software, PSHA software and reduction equations were used; consequently, minimum and maximum acceleration for useful life of 75-year and 475-year building were estimated. In order to assess the relative tectonic activity through the study area, sub-basins and stream network were extracted by using Arc Hydro Tools software based on the DEM and in turn, 134 sub-basins have been resulted. The six geomorphologic indices were used as follow: Stream length–gradient index (SL), mountain front Sinuosity (Smf), Ratio of valley floor width to valley height (Vf), Asymmetric factor (Af), Hypsometric integral (Hi) and drainage Basin shape (Bs). Eventually, after calculating the relative tectonic activity index (Iat), the studied area was classified into four tectonic activity classes in ArcGIS10.1 as very high, high, medium and low.
Stream Length–Gradient Index (SL): The SL index indicates an equation between erosive processing as streams and rivers flow and active tectonics. The SL is defined by Eq. (1) 
SL= (∆H/∆Lr) Lsc                                        (1)
where ΔH is change in altitude, ΔLr is the length of a reach, and Lsc is the horizontal length from the watershed divide to midpoint of the reach. The SL index can be used to evaluate relative tectonic activity.  The quantities of the SL index were computed along the streams for all sub-basins.
Index of Mountain Front Sinuosity (Smf):  Index of mountain front sinuosity is defined by Equation (2). 
Smf = Lmf ⁄ Ls                                             (2)
where Lmf is the length of the mountain front along the foot of the mountain in which a change in slope from the mountain to the piedmont occurs; and Ls is the straight line length of the mountain front. Smf represents a balance between erosive processes tending to erode a mountain front, making it more sinuous through streams that cut laterally and into the front and active vertical tectonics that tends to produce straight mountain fronts, often coincidental with active faults or folds.
Ratio of Valley Floor Width to Valley Height (Vf): Vf is defined as the ratio of the width of the valley floor to its average height and is computed by Equation (3).
Vf = Vfw/ [(Ald-Asc) + (Ard-Asc) /2)]                            (3)
where Vfw is the width of the valley floor, and Ald, Ard, and Asc are the altitudes of the left and right divides (looking downstream) and the stream channel, respectively. A significant relationship exists between the rate of mountain front activity and the Vf index. Consequently, the high Vf values conform to low uplift rates (Keller and Pinter 2002). The shape of a valley can also represent the Vf amount and uplift rate. Therefore, U-shaped valleys accommodate low Vf and high uplift.
Asymmetric Factor (Af): The asymmetric factor (Af) is a way to evaluate the existence of tectonic tilting at the scale of a drainage basin. The method may be applied over a relatively large area. Af is defined by Equation (4).
Af= 100(Ar/At)                                                   (4)
where Ar is the area of the basin to the right (facing downstream) of the trunk stream and At is the total area of the drainage basin. If the value of this factor is close to 50, the basin has a stable condition with little or tilting; while values above or below 50 may result from basin tilting, resulting from tectonic activity or other geological conditions such as lithological structure.
Hypsometric integral (Hi): The hypsometric integral is an index that describes the distribution of the elevation of a given area or a landscape. The Hi is independent of basin area. This index is defined as the area below the hypsometric curve and thus expresses the volume of a basin that has not been eroded. A simple equation that may be used to calculate the index is defined by Equation (5).
Hi = (average elevation - min. elev.) / (max. elev. - min. elev.)  (5)
Then Hi values were grouped into three classes with respect to the convexity or concavity of the hypsometric curve: Class 1 with convex hypsometric curves (Hi≥0.5); Class 3 with concave hypsometric curves (Hi<0.4); and Class 2 with concave–convex hypsometric curves (0.4≤Hi<0.5).
Index of Drainage Basin Shape (Bs): Horizontal projection of basin shape may be described by the elongation ratio, Bs, expressed by Eqation (6):
Bs = Bl/Bw                                        (6)
where Bl is the length of the basin measured from the headwaters to the mouth, and Bw is the width of the basin measured at its widest point. High values of Bs are associated with elongated basins, generally related to relatively higher tectonic activity. Low values of Bs indicate a more circular-shaped basin, generally associated with low tectonic activity.
Evaluation of Relative Tectonic Activity (Iat): The average of the six measured geomorphic indices (Iat) was used to evaluate the distribution of relative tectonic activity in the study area. The values of the index were divided into four classes to define the degree of active tectonics.
Results and discussions
Results of probabilistic seismic hazard analysis have shown that the minimum and the maximum acceleration for useful life of 75-year building is estimated as 0.33g and 0.45g and for 475-year one are 0.46g and 0.60g, respectively. These values are indicative of high risk in the studied area. Acquired values from geomorphologic indices and also acceleration zoning of the realm are indicative of high recent tectonic activities near Ipak, Hasanabad, Soltaniyeh and Avaj faults; they are extremely concordant with the obtained evidences and geomorphologic characteristics of the field samples. In this study, considering the diversity of the morphotectonic features, six morphometric indices relevant to the river channels, drainage basins, and mountain fronts were computed for every catchment, and consequently, a single index (Iat) was calculated from the these indices for each of 134 subbasins to define the degree of active tectonics. Finally, the Index of the Active Tectonic (Iat) was calculated through which the study area is classified into four tectonic activity classes, from very high to low; 1—very high (1.0≤Iat<1.5); 2—high (1.5≤Iat<2.0); 3—moderate (2.0≤Iat<2.5); and 4—low (2.5≤Iat). The distribution of the four classes of Iat has been presented in a well classified map. The indices have represented a quantitative approach to differential geomorphic analysis related to erosion and depositional processes which include the river channel and valley morphology as well as tectonically derived features, such as fault scarps. We also evaluated the outputs of the morphometric analyses based on field-based geomorphological observations. Thus, these results are proved to be extremely beneficial to evaluate relative rates of active tectonics of this region.
The values of Af show widespread drainage basin asymmetry related to tectonic tilting, particularly associated with Ipak fault. The values of Smf suggest that mountain fronts are tectonically active, and the values of Vf show that some valleys are narrow and deep, suggesting a high rate of incision. The parts with class 1 and 2 of the relative tectonic activity are located along the main faults of the region, such as Soltaniyeh, Avaj, Hasanabad and Ipak faults and show high correlation with observed landforms during the field investigations such as the direct mountain fronts, fault gorges, fault scarps, and deep v-shaped valleys. Besides, the high amount of the relative active tectonic index shows a good consistency with the recent tectonic activity, namely tilting and deformation of the Quaternary units, which is the indicative of the effect of compressive stresses, affecting the region.
In this study, according to the current tectonic activity using the Iat index, it was found that the study region represents a high current tectonic activity along the fault zones. The values of SL, Hi, and Bs were found to be high along Soltaniyeh, Avaj, Hasanabad and Ipak faults segments.
According to the earthquakes and probabilistic seismic hazard analysis in the study area, it can be said is worthy to note that some basins which are located among active faults, are seismically dangerous.  However, they show low relative active tectonic index (Iat)../files/site1/files/121/AleeiAbstract(1).pdf
Sassan Narimannejad, Alireza Jafari-Nedoshan, Ali Massumi, Abdollah Sohrabi-Bidar, Ali Ghanbari1,
Volume 12, Issue 2 (10-2018)

Local site conditions considerably influence all characteristics of the ground strong motion including the domain, frequency content, and duration. The level of such an effect could be considered as a function of geometry, properties of the materials embedded in the underlying layers, the site topography, and properties of excitement. Site effect fall into two categories: a) the effect of the surface soft layers triggered by the shear velocity differences between the soil layers and b) the surface and subsurface topography effects that lead to the wave reflection and refraction based on the site geometry, and subsequently enhance the level of amplification.
Since most cities have been constructed in the vicinity of or on sedimentary basins, geotechnical earthquake engineering devotes particular attention to effects of the sedimentary basins. Basin edge curvature deposited with soft soils are capable to trap the body waves and generated surface waves within the deposit layers. Such waves could create stronger and lengthier vibrations than those estimated in a 1D analysis that assumes the shear waves to be vertically propagated.
Although critically important, the 2D effect of the site has not been included in seismic codes and standards of the world. This might be due to the fact that the site effect depends on a number of parameters such as the site geometry, the type of wave excitement, properties of the materials, etc. that in return make it almost out of the question to make predictions about the effect. This study was an effort to compare the responses of four sedimentary basins with hypothetical geometries of rectangular, trapezoidal, elliptical, and triangular shapes in order to examine the effect of the geometrical shape of the basin on its responses and the extent of the response sensitivity to the excitation frequency of the wave. The study assumed the edge to depth proportion to be both constant and equal in all four basins so that the effect of the geometrical shape could be equally examined and compared in all four basins.      
Material and methods
In order to validate the results of the sedimentary basin modeling, firstly, ABAQUS finite element software was used to create a free field motion of a semi-circular alluvium valley in accordance with Kamalian et al. (2006) and Moassesian and Darvinsky (1987).  Then, the results from the model were compared with those from the above mentioned studies. The following descriptions are to present the model in details.
To evaluate the geometrical effect of the sedimentary basin on its response, the authors relied on the software to examine four sedimentary basins with the fundamental frequency (2.04 Hz). The basins enjoyed rectangular, trapezoidal, elliptical, and triangular geometrical shapes with a constant edge to depth proportion (49m to 300m respectively). The implicit method was also applied to perform the dynamic analysis. The materials were all viscoelastic and homogeneous. The soil behavior/treatment model was considered to be of a linear nature.  The Rayleigh damping model was used to specify the damping level. The soil element was a plane strain and SV waves (the Ricker wavelet) were used for seismic loadings in a vertical dispersion. The side boundaries (right and left) of the model were of a combinational type (viscous and free field boundaries); the down side boundary was composed of viscous. To achieve higher levels of wave absorptions, heavy columns were used as the free filed columns.
Next, it was the time to conduct the 1D analysis of the site. Three waves were in use in order to examine the effect of the frequency content of the excitation load on the basin response: 1) a wave with the dominant frequency of 1Hz that was out of the frequency range of all basins (2.04 Hz), a second wave with the dominant frequency of 2Hz that was close to the fundamental frequency of all basins, and a third wave with the dominant frequency of 4Hz. The waves were applied to a 2Dmodel. The results were compared with those obtained from a 1Dmodel in terms of the timing.
Then, the basin responses to all three waves (1, 2, and 4 Hz) were subjected to an individual analysis in order to examine the sensitivity of each basin response to its geometrical shape. Results indicated that while the responses of the rectangular and trapezoidal basins were significantly more sensitive to the excitation frequencies, the elliptical and triangular basins showed more stable behaviors to such frequencies. The final stage of the study was dedicated to examine the site 2D effect during the ground motion.
Results and Conclusions
According to the results of the present study, it could be suggested that the geometrical shape of the sedimentary basin has a significant effect on the responses of the field of seismic waves and that it could result in so different responses from the ones attained after a 1D analysis of the site. In addition, the pattern of the seismic waves’ responses is highly dependent on the geometrical shape and the frequency content of the seismic load. Also, the location where the maximum horizontal acceleration occurs along with the sedimentary basin depends on the excitation wave and varies accordingly. Further, it could be suggested that the site 2D effect results in both considerable amplification and an increase in the length of ground motion.
The results of the 2D analysis showed remarkable differences with their 1D counterparts: a 1.45 larger response for the rectangular basin, a 1.28 larger response for the trapezoidal basin, a 1.22 larger response for the elliptical basin, and a 1.19 larger response for the triangular basin.
With the frequency of 1 Hz where the excitation frequency is out of the basin range (i.e. the excitation frequency is below the lowest frequency of basin), the sedimentary basin did not show any signs of amplification and chaos (unlike two other frequencies); instead, it was a cause for de-amplification.
The frequency of 2 Hz that is subject to resonance resulted in amplifications (absent in 1D analysis) and there are traces of a reduction in the acceleration responses near to the edges of the basins. The proportion of the amplification (in the center of the basins) in 2D to 1D analysis was 1.4 for the rectangular basin, 1.28 for the trapezoidal basin, 1.22 for the elliptical basin, and 1.15 for the triangular basin.
S. M. Ali Sadreddini, Navid Hadiani,
Volume 13, Issue 3 (11-2019)

Past research studies have demonstrated that seismic ground motion can vary significantly over distances comparable to the dimensions of long span engineering structures. The accurate determination of earthquake ground motion at the base of long span structures such as dams and bridges whose piers are located on the valleys surface is one of the most important issues in earthquake engineering. In this paper, the spatially variable earthquake ground motions are generated at stations located on the valley slopes, considering the topography effect of a triangular valley. To this end, the simplified geometry of the valley of Masjed Soleyman embankment dam has been used for numerical modeling. The spatially varying ground motions are simulated by using spectral representation method. According to this methodology, the generated time histories are compatible with prescribed response spectra reflecting the wave passage and loss of coherence effects. This method assumes that the response spectrum is identical for all stations i.e., they have the same amplitudes and frequency content. This assumption is not valid for stations located on valley surface in which the amplitude and frequency content of the seismic waves are changed considerably by topography features. It is concluded that the proposed method in this study can lead to artificial spatially variable earthquake ground motions which can be readily reflect the amplification pattern of 2D triangular valleys.
Material and methods
In the first part of this paper, seismic response of a triangular valley is investigated through time history analysis conducted by using FLAC2D computer program. The geometry of the valley analyzed in this paper is chosen close to the valley of the Masjed Soleyman embankment dam. Dynamic analysis is conducted using an artificial earthquake generated by spectral representation method. The material properties are obtained based on the results of a comprehensive study carried out to identify the dynamic characteristics of two large embankment dams in Iran. Spectral amplification functions of seismic waves are calculated by dividing the response spectra of stations located on the slope of the valley to that in base of the valley. These functions are then used as target quantity for generation of spatially variable ground motions at points located on the valley. In this study, spectral representation method, the most widely accepted method for generation of spatially variable ground motions, is developed to take into account the topography effect. According to this methodology, the generated time histories are compatible with prescribed spectral amplification functions reflecting the wave passage and loss of coherence effects. The Harichandran-Vanmarcke coherency model is used to simulate spatially variable seismic ground motions.
Results and discussion
Based on the obtained results the maximum and minimum values of peak acceleration are yielded at the base and at the edge of the valley, respectively. The results indicate considerable increase of the acceleration RMS at points near the edge of the valley. Maximum spectral amplification is also observed at the edge of the valley. For all points located on the valley, the first peak spectral amplification occurred at frequency of 1.15Hz, which can be readily interpreted as the natural frequency of the valley. In order to evaluate the accuracy of the proposed method, the RMS and spectral amplification functions of artificial earthquakes are compared to target quantities. A very good consistency between the spectral amplification of artificial earthquakes and target spectral amplifications was observed in terms of both amplitude and frequency content.
The following conclusions were drawn from this paper.
- Artificial earthquakes generated using proposed method of this paper are in a very good agreement with the amplification pattern of the valley.
- The results of this study can be readily used to investigate the influence of spatial variability of earthquake ground motion on structures like bridges and dams whose supports are located inside the valley and are subjected to multi-support earthquake excitation.
- The proposed method of this paper is not limited only to the valley topography, but it can be effectively used in the generation process of non - uniform artificial earthquakes for stations located on other topography features. The latter can be carried out by establishing the spectral amplification functions of other topography features such as slopes and hills resulted from field or numerical studies.
Ali Saket, Seyed Mahmud Fatemi Aghda, Ahmad Fahimifar, Hossein Sadeghi,
Volume 14, Issue 4 (12-2020)

 Analysis of time, location and magnitude of foreshocks and aftershocks has been one of the most important cases for experts in various scientific fields such as: seismology, structural engineering and crisis management, and other interrelated fields. Since this analysis and the result of studies on seismotectonic and cases of earthquakes help us identify the foreshocks and aftershocks with the goal of decreasing losses and nervious stress of the injured community in quake-stricken areas and skilled crisis management. The cause fault of earthquake plays the important role in foreshocks and aftershocks of the earthquake. So, study on fault behaviour is a suitable method for analyzing and routing the basic parameters of foreshocks and aftershocks. Also, foreshocks and aftershock are important parts of any earthquake in a seismic area. The analysis of the basic parameters of the foreshocks is one of the most practical researches for reducing the risk of earthquakes. The identification of behavioral pattern of foreshocks can help researchers detect the active fault conditions for the occurrence of earthquakes in different areas. The present study is concerned with the study of behavioral patterns earthquakes, foreshocks, and aftershock of Zohan earthquake. Experience of large aftershocks in different parts of the world indicates that, following earthquakes and depending on seismic-tectonic conditions, large aftershocks are likely to occur in the earthquake-effected zone, which will aggravate the damage caused by earthquakes (Omi et al., 2013). The main factor contributing to the worsening of damage caused by aftershocks is the performance of structures that are weakened but not destroyed by main earthquakes and are, thus, highly likely to be destroyed by large aftershocks (Saket and Fatemi Aghda, 2006).
Material and methods
The present paper makes use of data collected in a real earthquake and similar expriences in other earthquakes for presenting a practical pattern for predicting primary earthquake patterns, determining the location, magnitude, and time of aftershocks. The target of this case is decreasing the effects of earthquake. To this end, we used the results from studies on basic parameters of foreshocks and aftershocks of Zohan earthquake, and 2012 earthquake in South Khorasan province. The rationale for selecting the aforementioned studies is: location of event, the Zohan earthquake, had been identificated as an area with high risk for the occurrence of earthquakes, although there has been no wide-scale earthquake in this area in the last two decades. These conditions are important causes for more concentrated studies on this area because there is a high chance for wide-scale earthquakes striking this area.
Result and Discussion
In this part of research, we conduct a study on the location, magnitude and depth of foeshocks. Some of the world-wide research suggested that these data can help to predict the time of  mainshocks. Studies conducted on the variations of frequency in foreshocks can follow this goal.
In this paper, the available statistical data such as periodical variations of seismicity in the weeks leading up to the main shock can be used as a tool for estimating the approximate time of a future important earthquake. The weekly variations of seismicity before Zohan earthquake indicate a relative increase and then decrease within a 100 km radius around the epicenter of the main shock.
Table 1: Variations of frequency of foreshock based magnitude before Zohan earthquake
Week before main shock Frequency of foreshock in the Radius of 100Km from main shock Frequency of foreshock(with M>2.5) in the Radius of 100Km from main shock
6 0 0
5 1 1
4 1 0
3 2 0
2 5 3
1 2 0
Studies on numerous earthquakes in Iran and other regions in the world show that the distribution of aftershocks can be related to fault type or the direction of principal stress (Saket and Fatemi Aghda, 2006) and (King et al., 1994). Whereas maximum Coulomb stress change is related to maximum principal stress in earthquakes, the concentration of aftershocks can coincide with the direction of maximum principal stress (σ1) of the causative fault in mainshock. Considering the direction of maximum principal stress and its adaptation to the scattering of aftershocks, the above hypothesis is confirmed.
Also studies on frequency changes and seismic quiescence of small aftershocks help us in predicting future aftershocks. The results the of presented research by Itawa (2008) on the World earthquake catalogue suggest that seismic quiescence theory is true for different regions of the world. Based on the results of the  study mentioned above, this case can be used as a tool for predicting large aftershocks in Zohan earthquake.

Fig 1. Adaptation of direction of maximum principal stress with scatering of the aftershocks of Zohan earthquake. a: direction of maximum principal stress (σ1) of the causative fault in mainshock. b- scaterring of the aftershocks
Table 2: Seismic sequience versus magnitude of aftershocks
Row Seismic Quiescence for aftershocks Aftershock Magnitude Data and Time of aftershocks
1 13 3.0 2012/12/05
2 36 3.4 2012/12/05
3 161 3.1 2012/12/05
4 3906 3.9 2012/12/08
In addation, frequency of aftershocks and certain time distance (seismic quiescence) between their can use precursors for detecting the time of large aftershocks. The relevant analysis in this study showed that methods such as: time series beside seismic quiescence can help in conducting a more accurate time forecast of large aftershocks.
  • The results of this research suggest that we can identify some of the charactristics of the main shock by focusing on location, magnitude and depth of foeshocks.
  • In Zohan earthquake, the direction of maximum principal stress is adpated to the scattering of aftershocks, and this case suggests that there is a specific relationship between them.
  • The relevant analysis in this study showed that the methods such as: time series beside seismic quiescence can help conduct a more accurate time forecast of large aftershocks../files/site1/files/144/saket.pdf

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