Ground Motion Intensity Research Articles

Dynamic responses and evolution characteristics of bedrock and overburden layer slope with space anchor cable anti-slide piles based on large-scale shaking table test

The study focuses on the anti-slide pile structure with space anchor cable, designing and conducting the large-scale shaking table test of bedrock and overburden layer slope with space anchor cable anti-slide pile system. The dynamic characteristics of bedrock and overburden layer slope with space anchor cable anti-slide piles are systematically explored from aspects of the overall acceleration field of the slope, the interface between overburden layer and bedrock, and the different depths of overburden layer. The results show that in the design of anti-slide pile with space anchor cable, the strength of the bedrock is utilized to resist the sliding force generated by the overburden layer in order to give full play to the role of the strength of bedrock in slope safety protection. The surface of the overburden layer appears a concentrated area of acceleration amplification and as the increase of ground motion intensity, and the concentrated area gradually shifts from the trailing edge of slope to the anchor head segment of anti-slide pile. Under accelerations in different peaks, the peak accelerations in the direction of free face and vertical direction have the asymptotic amplification effect, and the former is stronger. With the increase of ground motion intensity, the peak acceleration magnification decreases exponentially in direction of free face, while the peak acceleration magnification in the vertical direction presents a wavy distribution that first increases and then decreases.

Effects of Aftershocks on the Seismic Performances of Reinforced Concrete Eccentric Frame Structures

Strong aftershocks have the potential to cause accumulated damage in structures, a feature which has been reported in post-earthquake reconnaissance studies, particularly for eccentric or irregular structures. This study aims to investigate the seismic behaviors of eccentric RC structural models under mainshock–aftershock (MSAS) sequences. In this study, three-dimensional structural models with eccentricities of 5%, 10%, 15%, 20%, 25%, and 30%, and an eccentricity of 0 (symmetric structural model) are developed by changing the positions of the centers of the structural mass. A static pushover analysis and a nonlinear time history analysis are conducted on the structural models with different eccentricities considering unidirectional and bidirectional earthquake loading (including mainshock ground motion and MSAS sequences). The amplitude of the aftershock ground motion is scaled according to the structural damage levels calibrated with the inter-story drift ratio (IDR). Furthermore, the differences in seismic responses between the unidirectional and bidirectional eccentric structures are discussed. The results show that the peak displacements of the unidirectional eccentric structures under MSAS sequences are nearly 1.4 times higher than those under mainshock ground motions. The structural seismic responses under unidirectional earthquake loading are more sensitive to the intensity of aftershock ground motions than those under bidirectional earthquake loading. Compared with unidirectional eccentric structures, bidirectional eccentric structures are more sensitive to the intensity of aftershock ground motions and have larger torsional angles and more complex displacement trends. The maximum displacement and the maximum IDR of bidirectional eccentric structures under MSAS sequences can reach 1.5 times and 1.4 times of those under mainshock ground motions, respectively.

Data-driven analysis of crustal and subduction seismic environments using interpretation of deep learning-based generalized ground motion models

Studies on understanding the regional seismological differences based on the variations in the characteristics of the ground motion waves recorded during seismic events have provided independent insights into the different seismic environments of the world. This study aims to showcase the differences between three of the major seismic environments of the world including Japanese subduction, Chilean subduction, and Californian crustal. The study is based on developing deep learning (DL)-based surrogate generalized ground motion models (GGMMs) and analyzing them to understand the patterns between the earthquake source parameters and the resulting ground motion waveforms’ engineering characteristics. The GGMMs are developed using long short-term memory (LSTM) based recurrent neural networks (RNNs), which are trained using six earthquake source and site parameters as the inputs and a 25 × 1 vector of amplitude-, duration-, and energy-based ground motion intensity measures (IMs). The GGMMs are trained and evaluated using carefully selected large datasets of ground motion records from the Japanese subduction, Chilean subduction, and Californian crustal sources (∼2000 records from each source). The models are developed in two settings: i) three independent GGMMs using the three datasets of each source, ii) one combined GGMM using the combined dataset. While the former provides individual surrogate models of the regional seismic environments and allows relative comparison among the three environments, the latter acts as a global seismic surrogate model and allows comparison in absolute terms. The seismic environments are investigated by analyzing the two types of GGMMs using explainable artificial intelligence (XAI) and game theory based Shapley explanations (SHAP). As the direct physical study of the seismic environments is not generally feasible/practical, the proposed GGMMs surrogating the process becomes a source of knowledge. By interpreting them, inferences about the seismic environments are derived. Results indicate the peculiar nature of the earthquakes arising from the three seismic backgrounds, further emphasizing the importance of conducting independent regional seismic hazard and risk analysis. In particular, the role of magnitude and rupture distance is observed to have a significantly different impact on the different IMs of the three different environments. The study further sets a novel basis to utilize advanced DL and XAI methods in understanding convoluted physics and engineering phenomena.

Fragility curves accounting for uncertainties in material parameters and ground motion characteristics using a data driven surrogate model

This study uses a statistical surrogate model to develop fragility curves for an infilled reinforced concrete frame building, considering uncertainties in both material properties and ground motion parameters. The focal point of this study is a school building in Nepal damaged during the 2015 Gorkha earthquake. The school was instrumented, and its seismic response was simulated using a nonlinear numerical model. The model, developed following a recently proposed framework and extensively validated with the field data, is used in a parametric study conducted to identify the most influential material parameters (MPs). The model is then used in incremental dynamic analyses conducted to provide data for the calibration of a surrogate model. The three-staged least square statistical modeling approach is adopted to relate the influential MPs and ground motion intensity measures with important response quantities related to the peak and residual first-story drift ratios. The surrogate model is employed to generate fragility curves accounting for the two sources of uncertainty. The results indicate that accounting for uncertainties associated with the MPs can alter the fragility curves, causing a shift in the prediction of the median and dispersion of intensity measures.

Simulation‐based characterization of the variability of earthquake risk to buildings in the near‐field

AbstractRecent advancements in high performance computing platforms and computational workflow for regional‐scale simulations are enabling unprecedented modeling of fault‐to‐structure earthquake processes. Regional simulations resolving ground motions at frequencies relevant to engineered systems are becoming computationally viable and provide a new capability to improve understanding of the geographical distribution and intensity of risk to buildings and critical infrastructure. As computational capabilities advance, it is essential to move beyond illustrative single rupture realizations for scenario earthquake events towards the development of a full suite of rupture realizations that appropriately characterize the range of risk to building systems. The work described in this article investigates the application of a suite of fault rupture realizations with the objective of assessing near‐fault, site‐specific seismic demand variability for building structures. A representative high‐performance regional‐scale computational model is utilized to execute ground motion and building response simulations based on 18 kinematic rupture realizations of an M7 strike‐slip scenario earthquake. The fault rupture models for the scenario earthquake are created by systematically perturbing the hypocenter location and stochastically generating rupture parameters (slip, rise time, rake angle) to represent a breadth of ground motion intensities resulting from the spatial and temporal variabilities of an earthquake rupture process. The resulting seismic demand variability for three‐story (short period) and forty‐story (long period) steel moment‐resisting frame buildings is characterized in terms of the median and distribution of peak inter‐story drift ratio for a range of near‐fault sites. The full suite of 18 fault rupture realizations and approximately 280,000 nonlinear dynamic building simulations indicate that the three‐story building undergoes higher median seismic demand and significantly greater variability of demand at a given site than the forty‐story building, which has important implications for the level of certainty in predicting building performance during an earthquake. The simulations performed provide deeper insight into the relationship between fault rupture parameterization and building response, which is essential information for developing a representative suite of rupture realizations for specific earthquake scenarios.

Probabilistic-based seismic fragility assessment of earthquake-induced site liquefaction

As a very complex and uncertain problem, seismic liquefaction is affected by many factors, such as earthquake intensity, site conditions, soil properties, etc. During the past half a century, the state-of-the-art in analysis and evaluation of earthquake-induced soil liquefaction and its consequences as well as the state-of-the-practice in improving seismic stability to resist liquefaction have been made much progress. However, the fragility analysis and assessment for seismic liquefaction of sites have not been paid enough attention to. In this paper, the concept of seismic liquefaction fragility for building sites is proposed. The soil resistance to liquefaction and liquefaction possibility are expressed as a fragility function of ground motion intensity, which can be used to describe minor, moderate and severe liquefaction potential under different ground motion intensity. Combined with the existing research results of seismic liquefaction evaluation, the analysis method of liquefaction fragility is given. Taking a specific site as an example for liquefaction fragility analysis, it is found that taking the calculated exceedance probability of different liquefaction levels as the observation value, the liquefaction fragility function follows both lognormal distribution and log-logistic distribution. With the increase of liquefaction level, the median value of liquefaction fragility function increases, while the site liquefaction fragility curve moves to the right, which shows that the ability of the site to resist more severe liquefaction is increasing. When convolved with the analysis results of liquefaction triggering and hazard, the liquefaction fragility function can be a much efficient tool for seismic liquefaction risk analysis of specific sites.

Effect of near-fault directivity pulses on ground-motion intensity measure correlations from the NGA-West2 data set

This article investigates the correlation coefficients of ground-motion intensity measures for ground motions containing near-fault directivity velocity pulses. These correlation coefficients are necessary to quantify conditional multivariate intensity measure distributions and generate realizations from them for ground-motion selection. The empirical correlations between intensity measures representing ground-motion amplitude, frequency content, duration, and cumulative effects are calculated using the RotD50 definition and compared with published models. The impact of intensity measure definition as in RotD50, RotD100, and the geometric mean is also scrutinized. The sensitivity of the results to the considered ground motion set and the reference ground motion model are addressed in the computations. The results are compared with those from only non-directivity and mixed data sets based on the NGA-West2 database. The results indicate that the adopted data set has the largest influence on the variability of the empirically computed correlation coefficients. Given the multiple sources that contribute to uncertainty in these calculations, the authors conclude that existing models for predicting median correlation coefficients based on mixed data sets are sufficient for use with directivity, non-directivity, and mixed ground motions.

Numerical investigation on the characteristics of dynamic response and damage of a RC tall chimney considering vertical ground motions

Although seismic risk assessment models for structures have become more sophisticated, they have typically disregarded the effects of vertical ground motions (VGMs). Nevertheless, this trend is gradually shifting due to recent recordings and field observations that have demonstrated the potentially destructive effects of high VGMs.In this paper, a nonlinear finite element (FE) model of a 234 m reinforced concrete (RC) chimney is developed, with a focus on investigating its dynamic response and damage characteristics under the effect of VGMs. The results are compared with the case of a combination of horizontal and vertical ground motions (HVGMs). First, a time history analysis (THA) is performed under various VGMs input conditions. The findings reveal that the vertical seismic force increases with the intensity of ground motion. However, the distribution of the seismic force remains unchanged, with the maximum vertical seismic force occurring at 85% of the chimney height. Then, the seismic response of the chimney under HVGMs input conditions is examine, revealing that the maximum vertical seismic force increased by 4%–6%, but its distribution does not change significantly. Furthermore, the effect of the additional mass of the flue is considered, resulting in a significant increase in the vertical seismic force at the suspension points, leading to a change in its distribution. An abrupt increase of about 40% at 1/3 height and an increase of about 45% in the horizontal displacement at the top are observed. The paper also highlights the potential stress concentration and resultants cracks or damage caused by the opening of the chimney barrel.

Multi-index assessment of road blockage risk due to seismic event-induced building debris

The accessibility of road systems is key to facilitating emergency responses in the aftermath of a severe disaster. However, collapsed buildings and debris may cause road blockages, impeding disaster relief efforts after a major earthquake. This study aims to present an efficient and generic assessment method for evaluating the risk of road blockage due to seismic event-induced debris. First, the probability of building collapse in city blocks and the effects of building debris after an earthquake scenario are estimated based on building types, seismic design levels, soil conditions, and local ground motion intensities of the adopted earthquake scenario. Subsequently, the seismic risk of road sections is assessed by considering the collective effects of nearby street profiles, including building materials, heights, and the shape factor of city blocks. This study considers various interpretive building environment parameters and employs three post-earthquake risk indexes to represent different aspects of seismic risk of a road system, including passability loss, affected road length ratio, and road interruption severity. To demonstrate the applicability of the proposed method, the rescue routes in Taipei City, Taiwan, are adopted as a case study. The proposed method can effectively distinguish high-risk roads as valuable information, and the results have been provided to local government disaster relief units for reference.

The influence of seismic displacement models on spatial prediction of regional earthquake-induced landslides

Regional landslide prediction is a critical step towards achieving community resilience against landslides during earthquakes. We present a predictive methodology for regional earthquake-induced landslides that uses a pseudo-three-dimensional (pseudo-3D) procedure implemented on a digital elevation model (DEM). The methodology calculates a seismic displacement for every grid cell in the DEM as the basis for predicting the location and the size of landslide that is determined using a three-dimensional (3D) geometric projection based on topography. This “pseudo-3D” methodology for predicting landslides outperforms cell-based approaches. It has the advantage of deriving landslide number and size characteristics of individual landslides. We quantify the influence of seven commonly used seismic displacement models: four rigid, two decoupled flexible, and one fully coupled flexible. Seismic displacement model performance is evaluated by implementing a prediction for the 2015 Mw6.5 Lefkada earthquake event in Greece for which precise location and high-resolution landslide volume data are available for model validation and ground motion intensity measures are well constrained by nearby ground motion recordings. The 3D landslide inventory was created by topographically differencing pre-existing DEMs from post-event digital surface models derived from satellite and unmanned aerial vehicle (UAV) imagery. The inventory contains over 700 landslides, primarily shallow disrupted slides and rock slides, along with occasional occurrences of deep-seated, rotational failures. Qualitative comparisons between predicted and mapped landslides show that all seismic displacement models predict landslides that broadly overlap geospatially with most mapped landslides and the regions of high mapped landslide densities are predicted. A variety of metrics are used to quantify the prediction results: these include metrics such as landslide number and area density, as well as correctly predicted ratio, overlapped ratio, centroid distance, ground failure capture, and efficiency. The results show that the Rathje and Antonakos (kmax, k-velmax) model and the Saygili and Rathje (PGA, PGV) model correctly predict the most mapped landslides and obtain the highest prediction efficiency, but at the cost of the highest overprediction. The Bray and Macedo model achieves the best performance in predicting landslide number, area density, and location accuracy, but the correct prediction of the mapped landslides and the prediction efficiency are worse than other seismic displacement models. The results highlight the role of seismic displacement models in the prediction of regional earthquake-induced landslides and guide selection of the seismic displacement model depending on the objective of the prediction. Strength parameters also affect landslide prediction, and we demonstrate that all evaluation metrics vary widely due to variation of cohesion and friction angle, except for the correctly predicted ratio. More importantly, variation in prediction results due to the selection of seismic displacement models is found to be comparable to variation in results associated with strength parameter uncertainty. A critical slope parameter is proposed and defined as the flattest slope at which landslide triggering may occur for a given predictive model. As such, seismic displacement models that have lower critical slopes predict more landslides and differences in critical slopes for each seismic displacement model provide a parsimonious explanation for the different performances of the seismic displacement models in the regional earthquake-induced landslide prediction.

Seismic stability analysis of CSG dams considering the effect of tension crack based on genetic algorithm with an improved initial population strategy

CSG dams, which combine the characteristics of both gravity and rockfill dams, have traditionally been evaluated for seismic failure only in terms of tensile failure mode, similar to concrete gravity dams. However, recent studies have indicated that CSG dams may also be vulnerable to slope instability during earthquakes, which has not been sufficiently investigated. This study proposed a method to evaluate the seismic slope stability of CSG dams, which considered the impact of seismic tension cracks. In addition, an initial population strategy for the genetic algorithm (GA) was proposed to improve the process of seismic stability analysis of CSG dams. Using a 100 m high CSG dam as a case study, the seismic slope stability of CSG dams was studied under different ground motions with the proposed method. The results show that there is a potential risk of instability when the ground motion intensity reaches a certain level and the most dangerous slip surface could develop along the seismic tension crack on upstream dam surface. Additionally, the results also indicates that the proposed initial population strategy of GA can improve both efficiency and accuracy of stability analysis for CSG dams.

The ShakeMap Atlas of Historical Earthquakes in Italy: Configuration and Validation

Abstract Italy has a long tradition of studies on the seismic history of the country and the neighboring areas. Several archives and databases dealing with historical earthquake data—primarily intensity data points—have been published and are constantly updated. Macroseismic fields of significant events are of foremost importance in assessing earthquake effects and for the evaluation of seismic hazards. Here, we adopt the U.S. Geological Survey (USGS)-ShakeMap software to calculate the maps of strong ground shaking (shakemaps) of 79 historical earthquakes with magnitude ≥6 that have occurred in Italy between 1117 and 1968 C.E. We use the macroseismic data published in the Italian Macroseismic Database (DBMI15). The shakemaps have been determined using two different configurations. The first adopts the virtual intensity prediction equations approach (VIPE; i.e., a combination of ground-motion models [GMMs] and ground-motion intensity conversion equations [GMICEs]; Bindi, Pacor, et al., 2011; Oliveti et al., 2022b). The second exploits the intensity prediction equations (IPE; Pasolini, Albarello, et al., 2008; Lolli et al., 2019). The VIPE configuration has been found to provide more accurate results after appraisal through a cross-validation analysis and has been applied for the generation of the ShakeMap Atlas. The resulting maps are published in the Istituto Nazionale di Geofisica e Vulcanologia (INGV) ShakeMap (see Data and Resources; Oliveti et al., 2023), and in the Italian Archive of Historical Earthquake Data (ASMI; see Data and Resources; Rovida et al., 2017) platforms.

A simplified procedure for the prediction of liquefaction‐induced settlement of offshore wind turbines supported by suction caisson foundation based on effective stress analyses and an ML‐based group method of data handling

AbstractIn this research, a series of non‐linear dynamic finite element (FE) effective stress analyses were conducted to analyze the influence of the suction caisson geometry, ground motion intensity and contact pressure caused by the offshore wind turbine (OWT) on the settlement pattern and seismic demand of the OWT's structure on saturated dense sand. The baseline model and the FE procedure were validated using a database of well‐documented centrifuge tests. However, particular attention was given to the calibration campaign based on the measured system response quantities, such as the settlement, acceleration and pore‐pressure time histories. The FE results identified the contact pressure as an important state parameter caused by the OWT's mass; the governing ground‐shaking intensity measures that play a significant role in the derivation of an analytical framework for predicting liquefaction‐induced OWT settlements during major events are the shaking intensity rate (SIR), Arias Intensity ( and spectral acceleration at a period equal to 1 s (T = 1 s). The results revealed that approximating expressions derived using the modified least‐squares method (MLSM) reasonably capture the complex phenomenon of liquefaction‐induced settlement, with some exceptions at lower SIR values. Finally, to obtain the approximating expressions, the database was combined with a machine learning (ML)‐based group method of data handling (GMDH) that appropriately describes the interplay of multiple properties of the foundation soil, structure and seismic events while incorporating the effect of the interaction between the suction caisson, foundation soil, excess pore‐pressure generation and cyclic shear stresses.

Ideal-Pulse-Based Strong-Motion Duration for Multi-Pulse Near-Fault Records

ABSTRACT Serious damage to near-fault structures is caused mainly by velocity pulses in a ground motion, hence, the necessity to develop a pulse-related definition of strong-motion duration to adequately describe the intensity of near-fault ground motion. For a multipulse record, an ideal-pulse-based strong-motion duration, which is defined as the time interval between the beginning of the first pulse and the end of the last pulse in an ideal-pulse signal, is proposed. This strong-motion duration corresponds with the time interval of the occurrence of strong vibrations and energy accumulations in the original record. For near-fault records, pulselike characteristics can be completely presented within this duration. Meanwhile, the ideal-pulse-based strong-motion duration shows good performance in the estimation of structural responses. The elastic and inelastic displacement spectra of the original records agree well with those of the records shortened according to the proposed duration. The validity of applying the proposed duration to structural analysis is further verified by the nonlinear time history analyses of 3-, 9-, and 20-story steel moment-resisting frame structures. The proposed strong-motion duration accurately estimates nonlinear structural responses. It is proven that the ideal-pulse-based strong-motion duration can adequately describe the intensity of near-fault ground motions, both from the perspective of the energy accumulation process in a ground-motion record and that of the structural analyses subjected to these ground motions.

Shaking table tests on the seismic response of truss structure with air spring‐FPS three‐dimensional isolation bearing

AbstractTo investigate the isolation effect of the friction pendulum system (FPS) horizontal isolation bearing and the air spring‐FPS three‐dimensional (3D) isolation bearing in truss structure and the influences of long‐period ground motions on the isolated structure, the shaking table test of a truss structure is designed and conducted. The ordinary ground motions, near‐fault pulse‐like ground motions, and far‐field long‐period ground motions with different spectral characteristics are chosen to input into the structure, and the dynamic characteristics such as the acceleration, displacement, and stress of the truss are compared and analyzed. The horizontal frequency of the horizontal isolated structure is reduced after the horizontal isolation, while the vertical frequency is further reduced after 3D isolation. The isolation effect of nodal acceleration, nodal displacement, and member stress under 3D isolation is better than that of horizontal isolation, especially the vertical seismic response is significantly improved. When the ground motion intensity is small, the FPS horizontal isolation bearing slides little, and reducing the seismic response of the structure is limited. There is a better isolation effect of 3D isolated structure. The vertical frequency ratio Rf under ordinary ground motions is far away from 1 and close to 3, basically avoiding the main energy segment of the ground motions. The advantage of 3D isolated structure is relatively reduced under long‐period ground motions, which lies in the rich low‐frequency components of long‐period ground motions which are difficult to isolate effectively.

Seismic fragility analysis of steel moment frames using machine learning models

This study develops machine learning (ML) models for seismic fragility analysis of steel moment frames. Four ML methods – random forest, adaptive boosting, gradient boosting regression tree (GBRT), and extreme gradient boosting (XGBoost) – were employed for this purpose. Probabilistic seismic demand models, each representing the relationship between the seismic response of a type of structure and ground motion intensity, were used to construct the fragility curves based on nonlinear time history analyses of 616 steel moment frames subjected to 240 ground motions. The first three natural periods of steel moment frames and a capacity limit state defined by the maximum interstory drift were selected as input variables for the ML models. Two parameters (median and logarithmic standard deviation) of a fragility function were considered as output variables for the ML models. For each steel frame, the capacity limit state values considered for maximum interstory drift cover a wide range to generalize the fragility curve outcomes. The interquartile range method was used to ensure the quality of the dataset, and consequently 56,479 data points were used for the development of ML models. Based on model performance, the GBRT (R2 = 0.9986, for the testing dataset) and XGBoost (R2 = 0.9987) models are proposed as the best models for fragility analysis of steel moment frames. Finally, a graphical user interface for fragility analysis of steel moment frames was built based on the two proposed models, for easy access by practicing engineers. This study demonstrates the applicability of ML methods in practical design.

Evaluating the effectiveness of ground motion intensity measures through the lens of causal inference

AbstractWhen solving the performance‐based earthquake engineering (PBEE) integral, the engineering demand parameters (EDPs) are assumed to be independent of the “upstream” parameters used in ground motion models (e.g., magnitude and source‐to‐site distance) after conditioning on the intensity measure (IM). This paper formulates a methodology for evaluating this conditional independence assumption through the lens of causal inference (CI). From a causal perspective, the effect of an upstream parameter on the EDP of interest is partially mediated by the IM with the remainder having a direct influence on the EDP. An IM is judged to be desirable (from a conditional independence standpoint) if the mediated effect of the upstream parameter is maximized, which implies that the direct effect is minimized. In the language of causal inference (CI), the IM, EDP and upstream parameters are described as the “treatment”, “outcome” and “confounding” variables, respectively. It then follows that the best performing IM is the one that maximizes the effect on the EDP after controlling for the upstream parameters. A semi‐parametric model that employs double machine learning is used to estimate the causal effect. The methodology is demonstrated through a case study application utilizing the responses from five special steel moment frames analyzed using 240 site‐agnostic ground motions. Compared to sufficiency‐based assessments, the casual inference method produces findings that are more explainable using structural dynamics principles and invariant to the number of ground motions used in the evaluation.

Structural Pounding Effect on the Seismic Performance of a Multistorey Reinforced Concrete Frame Structure

During intense ground motion excitations, the pounding between adjacent buildings may result in extensive structural damage. Despite the provision of regulations regarding the minimum separation gap required to prevent structural collisions, the majority of existing structures are poorly separated. The modern seismic design and assessment of structures are based on the definition of acceptable response levels in relation to the intensity of seismic action, which is usually determined by an acceptable probability of exceedance. From this point of view, the seismic performance of a typical eight-storey reinforced concrete (RC) frame structure is evaluated in terms of pounding. In particular, the performance is evaluated using six different separation gap distances as a fraction of the EC8 minimum distance. As the height of the adjacent structure affected the required separation distance, the examined RC structure was assumed to interact with four idealized rigid structures of one to four storeys. The typical storey height was equal between the examined structures; therefore, collision could occur at the diaphragm level. To this end, incidental dynamic analyses (IDAs) were performed, and the fragility curves for different limit states were obtained for each case. Finally, the seismic fragility was combined with the hazard data to evaluate the seismic performance probabilistically.

Macroseismic Study of 4th January 2016, Manipur Earthquake, and its Implications

Abstract An earthquake of magnitude 6.7 M (Latitude 24.834N; Longitude 93.656E) on the Richter scale rocked in the Noney area, Tamenglong district, Manipur on 4th January 2016. The shock was strongly felt in most parts of the Northeastern states of India viz. Manipur, Nagaland, Meghalaya, Assam, and its neighboring countries Myanmar and Bangladesh. Macroseismic study was conducted to assess the intensity of ground motion and related damages caused by the earthquake. The damage incidences were mainly reported in structures constructed over the alluvial fill material. Deformations and development of ground fissures were observed in the epicentral tracts of Manipur and liquefaction phenomenon was observed in the Silchar area Assam. The study revealed that higher damage was confined to the area around Noney, Kabuikhullen, Nungba, Leimakhong, and Imphal valley areas in Manipur and Silchar town areas in Assam. Based on field observation, the degree of damage to building structures, and data gathered from the local population using the standard questionnaire, different intensity values were assigned to each locality. Isoseismal map was prepared by drawing the boundaries between different intensity areas at MSK-64 scale. The result indicates that the intensity was within the range of IV to VII. The maximum intensity was found VII in parts of Imphal, Tamenglong, and Silchar and very close to the epicentral tract area of Noney; and lowest intensity IV was observed in other parts of the northeastern states around Dimapur and Kohima in Nagaland state. The location of the epicenter of main shock (M 6.7) was at the intersection of the two major lineaments trending to ENE-WSW and NW-SE. The trend and shape of isoseismals drawn on seismotectonic/geological maps are elliptical along ENE-WSW direction and are found more closely spaced in the north and southern parts of the affected area. The elliptical nature of the isoseismals indicates that this seismic event was caused by movement along a linear surface. Furthermore, the orientation of elliptical isoseismals with a major axis trend in an ENE-WSW direction is almost parallel to the ENE-WSW trend of major lineament/fault in the area. As a result, the ENE-WSW lineament/fault trend appears to be the causative fault for this quake. In addition, one of the nodal plane (NP2) striking 83°, with dip 81° and slip (rake) 38° obtained from fault plane solution USGS shows a similar trend to the direction of generated elliptical isoseismals pattern confirming the event ocurred along a major tectonic lineament in a strike-slip mechanism.

Performance of parallel double pipelines under non-uniform seismic excitation

This paper investigates the structural safety of parallel double-buried pipelines under non-uniform seismic excitation considering the soil-pipeline interaction. A three-dimensional nonlinear numerical model has been established to study the effects of seismic wave propagation and ground motion intensity, as well as the pipeline internal pressure and spacing between the pipelines on their structural safety. The dynamic response of the parallel double buried pipelines was evaluated in terms of the acceleration amplification, settlement of ground surface, and strain, displacement, and elliptical deformation of the pipeline. The results demonstrate that the seismic response of buried pipelines under non-uniform excitation has obvious nonlinear characteristics, especially when the loading intensity is high. It is found that the internal pressure has virtually no effect on the site acceleration response, but it amplifies the settlement of the ground surface. Meawhile, it inhibits the elliptic deformation of the pipeline. Furthermore, the variation of the elliptic deformation of parallel buried pipelines is found to be the same for different pipeline spacings considered in this study. On the other hand, the pipelines spacing has a significant influence on their seismic response as the interaction between the two pipelines gradually decreases with the increase in the spacing.