Journal of Seismology and Earthquake Engineering
Volume:22 Issue: 1, Winter 2020

When a relatively strong earthquake occurs, it changes the conditions for failure in its proximity and alters the occurrence probability for future events. In this study, the occurrence probability of future earthquakes with magnitudes Mw≥5.8 onthe basis of Brownian passage-time (BPT) and Weibull Time-dependent models is calculated for the next 10, 30 and 50 years in the Zagros region. According to the method used in recent years, initially, the Coulomb stress changes caused byearthquakes interaction is computed on each fault. Then, the impact of this stress change on the occurrence probability of next characteristic earthquakes is calculated, taking into account both permanent (clock advance) and transient (rate-and-state) effects of stress changes. We concentrated on the long term slip rate uncertainties by generating 1000 random numbers using the Monte Carlo technique. We find that earthquake interaction effects in this region are small.Thus, permanent and transient effects of stress change do not affect the calculated probabilities very much. The maximum probability is related to the Kazerun fault that shows the high seismic activity of this fault.

In India, many regions under high seismic risk are located on deep soil deposits extending up to several hundred meters of depth. Deep sedimentary deposits are more prone to earthquake hazard. The Indo-Gangetic Basin (IGB) is located in the vicinity of Himalayan Frontal Fault (HFT) and the presence of thick alluvium makes it more vulnerable to seismogenic sources and hence, its characterization is required. In the present study, six sites in Uttarakhand are characterized by using the joint fit Inversion method from the data obtained from Multi Channel Analysis of Surface Waves (MASW) technique with a combination of Horizontal-to-Vertical Curve (H/V) from microtremor studies. Further, seismic hazard assessment for a scenario earthquake (Mw= 8.0) is performed to study the behavior of IGB. There is an increase in spectral acceleration at sites with deep soil profiles and amplification also increases due to the presence of deep soil deposits in this region. This indicates that these sites suffer from high liquefaction potential as compared to shallow soilprofiles. Moreover, peak ground horizontal accelerations at bedrock level are computed by dividing the study area into seven seismogenic source zones. On a regional scale, the b value is relatively high for seismic zone VI indicating high locally concentrated stress and fracturing. Also, the value of l is highest in seismic zone IV and lowest in seismic zone II. The estimated return periods for R6.0, R7.0 and R8.0, represents the seismic zone IV as the most active in the whole region. The estimated hazard parameters are possibly in agreement with the reported hazard parameters in the literature. Seismic characteristics of seismogenic source zones may be used for earthquake engineering purposes, e.g. assigning the severity of input motions for earthquake resistant construction.

Hazard plays a vital role in assessing the risk of any area. For earthquake hazard estimation, it is essential to obtain ground motion records from various seismic stations. However, it is not always easy to get ground motion data. The present study is an attempt to generate ground motions of the recent September 24, 2013, Pakistan earthquake using modified semi-empirical approach, which is based on ω2 model. The first part of the method considers a time series having the basic spectral shape of acceleration. The deterministic model of rupture source has been used in the second part of the method to simulate the envelope of accelerogram. For the study, a MATLAB code is written to generate synthetic accelerograms at stations Awaran, Panjgur, Tagas, Korak, and Gajar. The results are compared with GroundMotion Prediction Equation (GMPE) proposed by Ramkrishnan et al., in 2019 [1]. The PGA values obtained from modified semi-empirical method gives satisfactorily good results in comparison with the PGA values from GMPE. However, slight variation is observed between synthetic accelerogram PGA values and GMPE values at Gajar, Korak, Tagas, Panjgur stations.

Undrained behavior of aggregate-clay mixtures in its natural or compacted state, which is used as the core of embankment dams or liner of waste disposal systems, has great importance for geotechnical engineers. Previous studies have shown that excess pore water pressure plays an important role when dealing with cyclic/dynamic behavior of aggregate-clay mixtures. An extensive testing program was conducted on compacted sand-clay mixtures to investigate effects of aggregates on the cyclic behavior of the mixtures under strain- and stress-controlled cyclic loads utilizing triaxial and torsional shear equipment. Clay content was varied from 100 to 40% by volume in tested specimens. Isotropically and anisotropically consolidated specimens were tested under vertical effective stresses of 100 and500 kPa. The aim of the various loading conditions and numerous experiments was to investigate cyclic pore pressure build-up in the mixtures, and developing a pore pressure model based on dissipated energy. The main advantage of the model is that it can capture opposite trend of pore pressure build-up with aggregate content in strain-, and stress-controlled loading. The model is then verified with cyclic triaxial tests on ceramic beads-clay mixtures.

There are some cases, such as irregular or complex structures, in which the simplified analysis methods recommended by prevalent seismic codes are not able to yield results with acceptable precision. In such circumstances, the use of Non-Linear Time-History Analysis as the most robust response analysis approach is mandatory. This method is usually very time-consuming (mainly due to the small time steps). Therefore, any technique to reduce the computational cost, whilekeeping results in an acceptable range of precision, would be desired. There are some methods in the literature to increase the size of time step and simplify the recorded accelerograms by modifying time series. Although these methods may show negligible bias in results in terms of maximum response values of simple structures, they, definitely, impose some error due to the manipulation in the frequency content of the original signal. In this paper, an S-Transform basedsim-plification procedure is introduced to overcome the drawbacks of available methods. The proposed method enables users to trace and compare the timefrequency variation of original and simplified signal to keep the general timefrequency pattern of signal and prevent the undesired omissions of components. Eleven strong ground motion records were selected to be used in the efficiency evaluation of the proposed method. The results of analyses for a range of single and multi-degree of freedom non-linear dynamic systems confirm the ability of shortened records to represent their original counterparts in terms of response characteristics. The results show that by a reduction of 71% in the analysis cost, the maximum observed error in the estimation of collapse of MDOF structures will be lower than 10%.

In order to determine the performance level of steel structures or to strengthen them, it is necessary to determine the ultimate capacity of their connections under the influence of extremely low cycle fatigue caused by cyclic load. On the other hand, the ultimate capacity or failure of the connections, under unavoidable monotonic loadings such as explosions or fires, needs to be determined in order to predict the progressive collapse in structures utilizing intermediate and/or special moment frames. In this study, the ultimate capacity of welded connections, subjected to monotonic loading, is estimated using the Stress Modified-Critical Strain model (SMCS). However, the Cyclic Void Growth Model (CVGM) is used to investigate connection capacity under cyclic loading. These models could be used to estimate the ultimate capacity of connections to determine the performance levels of the structures where it is not practical or possible to test laboratory specimens. In this paper, the ultimate capacity of connections are obtained based on the crack initiation criterion in three types of moment connections, namely reduced beam section (RBS), welded unreinforced flange-welded web (WUF-W), and increased beam section (IBS) moment connections; (1) subjected to monotonic loading in the column removal scenario by using the (SMCS) model, and (2) under cyclic loading by using the (CVGM). This research shows that by using the ductile fracture models, it is possible to predict the ultimate capacity and fracture mode of the weldedmoment connections with great accuracy. The results of this investigation, using fracture models, indicate that out of the three types of connections, the seismic rotational capacity of the IBS moment connection is the largest (0.05 radians), next is RBS (0.044 radians), and WUF-W is the last (0.04 radians) with the least rotational capacity under cyclic loading. The results also reveal that the rotation capacity of the connections under monotonic loading is two to three times thecapacity of the same connection under cyclic loading (IBS:0.20 radians, RBS: 0.16 radians and WUF-W :0.147 radians).