پژوهشنامه زلزله شناسی و مهندسی زلزله
سال پانزدهم شماره 4 (پیاپی 58، زمستان 1391)

This study continues exploring methodologies to improve earthquake-explosion discrimination using regional amplitude such as ARMA coefficients. The earliest simple source models predicted P wave amplitudes for explosions should be much larger than for earthquakes across the body wave spectrum. However، empirical observations show that the separation of explosions from earthquakes using regional P amplitudes is strongly frequency dependent، with relatively poor separation at low frequencies (~1 Hz) and relatively good separation at high frequencies (>~3 Hz). The authors of this paper demonstrate this by using closely located pairs of earthquakes and explosions recorded on common، publicly available stations at test sites around the world. It was shown that this pattern appeared to have little dependence on the point source variability revealed by P-waves and surface waves. Therefore، S-waves resulted by explosions can be predicted from the P-wave models via a frequency dependent transfer function. A recent model by Allamehzadeh (2011) shows that the explosion ARMA coefficients can be modeled using the P-wave spectra with the corner fre-quency reduced by the ratio of the wave velocities، which seems to imply a direct generation of S-waves in the source region. A number of nuclear tests were examined from around the world in the light of these models. In this paper، the problem of seismic source classification is considered at regional distances. The neural network classifier is fed by Nonlinear AutoRegressive Moving Average (NARMA) coefficients extracted from raw data as feature set. The authors have devised a supervised neural system to discriminate between earthquakes and chemical explosions applying filter coefficients obtained from the windowed P-wave phase (15 sec). First، the recorded signals are preprocessed to cancel out instrumental and attenuation site effects and obtain a compact representation of seismic records. Then، a Quadratic Neural Network (QNN) system was used to extract nonlinear ARMA coefficients for feature extraction in the discrimination problem. These coefficients were then applied to a probabilistic network for the purpose of training and classification. The results have shown that the overall combination of this feature extraction and classifier structure leads to a suitable seismic discrimination performance. The events tested include 36 chemical explosions at the Semipalatinsk test site in Kazakhstan and at test site in China as well as 61 earthquakes (mb = 5. 0-6. 5) recorded by the Iranian National Seismic Network (INSN). In this study، we implemented feature extraction-feature discrimination approach to the seismic discrimination problem by using Neural Networks. As the discrimination features، various power or ARMA characteristics of seismo-grams were used that are typically different for earthquakes and explosions. The discrimination problem was solved by application of statistical pattern recognition techniques.

The Zagros Fold-Thrust Belt (ZFTB) is a collision zone، which is formed due to the northeast motion of the Arabian plate toward the central plateau of Iran. At the surface، the Zagros consists of long، linear anticlinal ridges that form a series of ranges from eastern Turkey in the NW to the Strait of Hormuz in the SE، a distance of about 1200 km. Structural and seismological features of Zagros belt were studied by a new approach (Fractal). For this aim، fundamental data of faulting and seismicity، distribution of magnitudes، epicenters، and faults، were reanalyzed. The deep-seated master thrust faults bordering the morphotectonic units of the Zagros are: (1) the Main Zagros reverse fault (MZRF); (2) the Main Recent Fault (MRF); (3) the High Zagros thrust Belt (HZTB); (4) the High Zagros fault (HZF); and (5) the Mountain Front Fault (MFF). The scale-invariant geometry of many natural fracture systems and earthquake populations suggests that fault structure and seismicity can often be described in terms of fractal sets. In principle، the various fractal dimensions may be used as a quantitative measure of the degree of heterogeneity of seismic activity in fault systems. These in turn are controlled by the heterogeneity of the stress field and the pre-existing geological. However، fractal dimensions obtained by different methods generally reflect different aspects of the scale invariance، and need not be equal to or even positively corre-lated with one another. Parameters of fractal analysis are fractal dimension (correlation dimension DC and capacity dimension D0) and seismic b value. We investigate the spatial variations of seismicity along these zones in an attempt to investigate fault complexity along strike، quanti-fied by the Gutenberg-Richter b-value and the fractal (correlation) dimension of earthquake epicenters، by using the correlation integral method، from magnitude distribution (b value) through maximum likelihood method. Temporal and spatial variations of these parameters computed from different techniques are related with clustering properties of seismicity (correlation dimension)، density and complexity of faulting and tectonic stress rate (b value). The investi-gation covers instrumentally recorded earthquakes of magnitude M > 4. 5 occurring between 1900 and 2011. We find systematic spatial variations which may be related to structural or mechanical variability along strike. The correlation dimension (2. 15 < D < 2. 47) and b (0. 3 < b < 1. 6) value، respectively computed from the earthquake epicenter and magnitude distribution show significant temporal and spatial variation related with seismotectonic feature of fault zones. Besides، some parameters of fault zones were determined to have bifractal properties. The results show that the fractal dimension D in the Zagros thrust belt is changed between 2. 1 to 2. 47. The fractal dimension along the thrust zone shows a significant variation for the different fault segments. This maybe encouraging that the fractal analysis can be used to identify structural variations in a seismotectonically complex area. This statistical correlation is stronger when more objective seismic zoning is carried out (based on number of events) rather than more subjective seismotectonic zoning in common use in seismic hazard analysis.

There are different methods for seismic analysis of topographic features which include analytical، semi-analytical and numerical methods. In the analytical methods extracted from matched asymptotic expansion of wave and Bessel/Hankel functions، responses are presented in terms of summation limit as closed-form solutions. Based on the semi-analytical methods، the problem is decomposed into two primary and secondary parts، which can be solved analytically and numerically. According to what is observed in the nature، the responses of analytical or semi-analytical methods have high accuracy، various types of arbitrarily shaped topographic features cannot be applied for modeling in reality. It results in the development of numerical methods which have good flexibility. These methods can be divided into three types including volumetric، boundary and mixed methods، This paper presented the most important studies that have been conducted in the past half-century (1960-2011) on the mentioned topics. The above mentioned studies are classified based on the used methods، prepared model type and publication year. Despite the development of volumetric methods، such as finite element method (FEM) or finite difference method (FDM) and their simple formulations، the whole body including the inside and boundaries must be discretized in order to model the topography features. This process requires too much time and data. As a result، special attention has been given to the Boundary Element Method (BEM) among the various existing numerical methods during the recent two decades. In this method، only the boundaries of the media need to be discretized in order to analyze an elastic continuous media. Two BEM formulations have been proposed to be used in modeling، including full-plane and half-plane. First، the formulas are classified and the governing boundary integral equations are presented. Then، the related studies based on the full-plane and half-plane fundamental solutions are reviewed. It is worth mentioning that out-of-the-plane wave (SH wave) has been considered as the case study in all studies investigated in this paper.

Reusing or hygienic burial of huge amount of waste tires released in the nature is a big environ-mental problem. In some cases، soils should be improved for the use in geotechnical projects. To overcome the environmental problems and also، reusing of these waste materials، researchers are studying about civil engineering aspects of usage of waste tires. These factors may come together، leading to finding appropriate applications of waste tires. Waste tires can be used as a whole tire، chips and also shreds. A number of investigations have been carried out on shredded and chips waste tires reinforcing sands. These are، to the date، limited to those carried out on the randomly distributed of shreds in sand-shred mixtures. Using soil-tire mixture as a reinforced soil increases the soil shear strength parameters in geotechnical branch of civil engineering aspect. Results of large scale direct shear tests show that with increasing normal stress، shred contents، and degree of compaction of shred-sand mixtures، the friction angle of sand-shredded mixtures increases. Also results show that the aspect ratio of shredded tires has an important effect on shear strength parameters of reinforced sand. It is shown that for a given width of shredded tires، there exists only a sole optimum aspect ratio، which gives the absolute maximum friction angle of the mixture، regardless of shred contents and compaction degree. In this research، strip shallow foundations located on a reinforced soil by tire is modeled. Using three different contents of tire in the reinforced sand; 15%، 30% and 50%، different depth of reinforced soil (sand-tire chips mixture) beneath the foundation is pseudo statically analyzed. The analyses are based on 2D PLAXIS software and foundation settlement excited by different horizontal pseudo static accelerations are studied. Using sand-tire shreds shear strength parameters based on laboratory large scale direct shear tests in numerical 2 dimensional models، the settlement of reinforced soil is studied in static and pseudo static analyses. The results are compared with the results based on unreinforced sand. Two different degrees of compaction sand-tire chips are numerically studied، loose and compacted mixture degree of compaction. The results show that the benefits of using these sand-tire shreds mixtures، in loose compaction are more important and economical. Although the effects of compaction degree are important، it seems that tire shred contents as well as the width and depth of using sand-tire mixture، are also important and should be understood. Therefore، in this research، these different parameters are numerically studied in both static and pseudo static analyses. The obtained results show that using soil-tire shred mixture beneath the strip foundation reduces the settlement and also pseudo statically forces effects to the foundation. It can be understood that using the waste tires can reinforce the sand، increase the shear strength parameters and also reduce the settlement beneath the strip foundations.

The main objective of this study is to introduce and evaluate the seismic behavior of post tensioned column base connection in self centering steel moment resisting frames (SCMRFs). The components of the PT column base connection include PT high strength bars for clamping and restoring forces، buckling restrained steel plates for energy dissipation and damping، reinforcing plates for increasing shear bearing and shear yielding resistance، and keeper plates for increasing shear resistance. Buckling restrained plates and keeper plates are welded together. The PT bars are anchored between half-height of the first story column and that of basement column. Structural damage at column bases in the SC-MRF is likely to occur due to yielding of the columns. Columns in the SC-MRF are continuous and thus the bottoms of the columns are high demand locations in terms of moment، shear and axial force. Therefore، the column bases in the SC-MRF may suffer damage (e. g.، plastic hinging) under a major earthquake. This damage results in permanent residual deformations of columns affecting the self-centering capability of the SCMRF system. To eliminate the structural damage in columns as well as to enhance the self-centering behavior of the SC-MRF، a PT column base connection is introduced for use at column bases. By using this connection، the plastic hinge in column bases is removed and plastic deformation is shifted into energy dissipation device. A posttensioned column base connection is modeled in OpenSees software (i. e.، Open System for Earthquake Engineering Simulation) to evaluate the seismic behavior of this connection. The materials used in the model of connection are: Steel01 for beam and column، Elastic perfectly plastic for Post tensioned bar، Elastic-no-tension for modeling gap opening and Steel02 for energy dissipation device. Nonlinear beam column element was used for beam and column element. Also Truss element was used for post tensioned bars، gap opening and energy dissipation device. The cyclic loading was applied to this connection. Based on the analysis results، it was found that the introduced connection dissipate energy of earthquake without any residual drift. The effect of post-tensioned bars diameter، level of post tensioning and energy dissipation device size in connection behavior were investigated. The initial stiffness of connection at all component is equal to conventional connection. Buckling restrained plates size affects energy dissipation of connection. When the buckling restrained plate size increases، the amount of energy dissipation is increased. The post yielding stiffness of connection in this condition increased. When the post-tensioning level of bars grows، the compression moment for development of gap opening at grade beam interface and post yielding stiffness of connection increased. The increase of diameter of post-tensioned bars also increases the stiffness of connection.

In August 11th 2012، at 16:53 and 17:04 two earthquakes with magnitudes of 6. 3 and 6. 4 occurred in East-Azerbaijan province، North-West Iran. The epicenter of the event as well as the main damaged area was close to Ahar، Varzaghan and Heris. The number of victims has been reported 306 people and more than 1500 people were announced as injured. Immediately after the events، IIEES dispatched a reconnaissance team to the area. This paper presents a preliminary report of geotechnical and structural damage according to the observations during this reconnaissance trip. The field observation revealed the existence of surface fault rupture with an E-W trending right-lateral strike-slip. Besides، some geotechnical instabilities such as landslides and site effects have been caused by the earthquake. According to the landslide instability، different earthquake-induced landslides have been occurred over the stricken area، with the domination of disrupted slides and falls in rock. Based on the geological map of the stricken area، the existence of the Pliocene lithology in some parts increases the sliding potential. Consequently، the recent earthquake reactivated some of the previous landslides which have occurred during the past decades. According to the topography and site effects، the highest damage states in the Varzeghan city were observed in buildings which are located next to the river. In the Ahar city، many of the damaged buildings were concentrated in the highest zones of the city. The Sattarkhan، Yamchi، Herris، Sabalan and Khodafrin embankment dams and Shahryar concrete dam were observed. Only the Sattarkhan dam suffered some minor damages and no observable damage reported in other dams. In this dam، some cracks in upstream-downstream direction were observed. The intake tower of the dam was also rotated slightly and a 6mm relative displacement was observed at the level of the deck of its access bridge. Moreover، some lightings of the access bridge to the intake tower were broken. The Sattarkhan Dam was operable after the earthquakes. During the inspection from the gallery، no evidence of abnormality including water discharge from the core and cutoff curtain were observed. The main damage occurred in adobe and non-engineered buildings mainly constructed in rural area. Considerable human loss was concentrated in the same area as a consequence of weak construction quality and heavy material. Some important buildings including hospitals and office buildings in the area were non-operational after the earthquake due to improper performance of non-structural systems and equipments. Four bridges were observed in the stricken area. Structural damage and failure of serviceability did not occur. The skewed bridge in Varzaghan experienced rotation of decks and pounding of decks to each other. This caused light damage to the bridge.