Faculty Publications
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Item RECENT DEVELOPMENTS IN SYNTHESIS OF EARTHQUAKE MOTIONS USING LINEAR JOINT TIME FREQUENCY ANALYSIS TECHNIQUES(International Association for Earthquake Engineering, 2021) Ramkrishnan, R.; Devaraj, D.; Kolathayar, S.; Sitharam, T.G.Temporal distribution of the frequency contents of a multi-component signal like seismic motions are not captured and well-represented in Fourier Transform (FT) techniques. Linear Joint Time-Frequency Analysis (LJTFA) addresses this issue and can transform and represent a signal in not only time domain and frequency domain, but in time-frequency domain simultaneously. Considering the better resolution and less spectral spillage when compared to Short Time Fourier Transform (STFT) and less complexity when compared to Wavelet Transform (WT), Gabor Transform (GT) is adopted in the current study. Actual recorded time-histories from recording stations in Japan had been considered for a LJTFA based synthesis of earthquake motions in this study considering the high seismicity of the area and large number of data available. Recorded time-histories of 23 earthquakes throughout Japan has been collected from K-Net and Kik-Net Strong Motion Seismograph Network of Japan and is categorized according to various Magnitude and hypocentral distances. Events of magnitude ranging from 5 to 5.5 and hypocentral distances 0 to 100km is sorted and GT is applied to transform the signals to their time-frequency domain and estimate their Gabor amplitude coefficients. Mean Gabor amplitude coefficients are estimated for different Magnitude (Mx) and Distance (Dy) combinations like M5D0-25, M5D25-50, M5-5.5D0- 25, and M5-5.5D25-50. Using an inverse GT process; Gabor Expansion (GE), the mean transformed Gabor amplitude coefficients are used to reconstruct and synthesize a time-history which doesn’t compromise on the quality of their spectral and frequency contents, thus yielding reliable synthetic seismic motions. Response spectra is developed from the actual and synthesized time-histories and are compared. A statistically good fit in terms of the coefficient of determination factor, R2 is observed between the actual and synthetic response spectrum developed. © 2021, International Association for Earthquake Engineering. All rights reserved.Item Development of Region-Specific New Generation Attenuation Relations for North India Using Artificial Neural Networks(Springer Science and Business Media Deutschland GmbH, 2021) Huang, H.; Ramkrishnan, R.; Kolathayar, S.; Garg, A.; Yadav, J.S.Present study focuses on developing region-specific New Generation Ground Motion Prediction Models using Artificial intelligence technique for North India purely based on a measured ground motion data from specific region. Simple single hidden layered feed forward multilayer perceptron networks with back-propagation learning algorithm are used. A total of 280 data points of recorded strong motion data from the Kangra and Uttar Pradesh (UP) arrays, made available by the Program for Excellence in Strong Motion Studies (PESMOS), were used to train these networks. The first model predicts Moment Magnitude for a given Hypocentral Distance and Peak Ground Acceleration. The second model predicts Peak Ground Acceleration (PGA) for a given Hypocentral Distance (HPD) and Moment Magnitude (MM). Performance analysis, Uncertainty analysis and analysis of interactive effects have been done to test the reliability of the generated models. Optimization analysis was also performed to predict possible inputs of the models for a given set of outputs. Models have performed reasonably well for the given amount of non-linearity in the data. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Joint Time Frequency Analysis Based Synthesis of Acceleration-Time History and Response Spectra for Japanese Earthquakes(Springer Science and Business Media Deutschland GmbH, 2022) Ramkrishnan, R.; Devaraj, D.; Kolathayar, S.; Sitharam, T.G.Time–Frequency Analysis (TFA) techniques help to obtain the ideal time and frequency occurrence characteristics of earthquake motion confined in a seismic recorded signal. Time-histories from recording stations in Japan has been adopted in the present analysis, considering a large number of available data. The seismograms were transformed using Gabor transform, a Linear Joint TFA method, to assess their frequency content by generating their Gabor coefficients. Average Gabor coefficients were estimated for recorded seismograms within a magnitude range of 5.5–6.0 and hypocentral distances ranging from 0 to 50 km. The estimated average Gabor coefficients were used to synthesize a generalized acceleration-time history for the specific distance and magnitude ranges using Gabor Expansion, without compromising the frequency content of the waves. Additionally, it is demonstrated that the response spectra of the synthesized signal and the original signal match very well. These response spectra will be valuable for the nonlinear investigation of structures in this region. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Synthesis of Linear JTFA-Based Response Spectra for Structural Response and Seismic Reduction Measures for North-East India(World Scientific, 2020) Devaraj, D.; Ramkrishnan, R.; Prabu, T.; Kolathayar, S.; Sitharam, T.G.North-East India (NEI) has a long history of devastating earthquakes due to the complicated tectonic setting of the region. A shortage of sufficient recorded time-histories from the region calls for a synthesis of accelerograms for dynamic analyses. In this study, a novel Joint Time-Frequency Analysis (JTFA) technique is adopted for the synthesis of accelerograms, considering the non-stationary behavior of earthquake waves. JTFA is used for analyzing the signals in a joint time and frequency domain to better understand its characteristics and synthesize signals without compromising its inherent characteristics like frequency content and amplitude. Synthetic accelerograms are developed using JTFA techniques for different magnitude and distance ranges between 5 to 6.8 and 0-480km and response spectra are developed. Synthesized generalized accelerograms and their response spectra are compared with actual signals in the same magnitude-distance ranges and were found to match. A comparison of the frequency contents of actual and synthetic signals was also carried out using Fourier Transforms and spectrograms (SPs) and was found to be in good agreement. Further, a comparative study of various earthquake reduction measures for NEI is carried out for a scenario earthquake using the synthesized data, and the best suitable structural input for the region is recommended. © 2020 World Scientific Publishing Company.Item Probabilistic seismic hazard analysis of North and Central Himalayas using regional ground motion prediction equations(Springer Science and Business Media Deutschland GmbH, 2021) Ramkrishnan, R.; Kolathayar, S.; Sitharam, T.G.Recently developed region-specific GMPEs are used for a comprehensive seismic hazard analysis (SHA) of the North and Central Himalayas (NCH) using a probabilistic approach considering two source models. Vulnerable seismic sources in the areas are identified based on the Seismotectonic Atlas (Dasgupta et al. 2000), published by the Geological Survey of India. An up to date, homogenized and declustered earthquake catalogue is compiled from various sources, with earthquake data since 250 BC, to create a new digitized seismotectonic representation of the region. Regional seismic zones having similar seismicity are recognized based on the Gutenberg-Richter (GR) parameters and the region is delineated into 5 seismic zones. The study area is divided into grids of size 0.05° × 0.05° and the hazard in terms of Peak Ground Acceleration (PGA) at the centre of each grid point is estimated and presented as hazard maps for individual seismic sources, maximum of all sources, and average of both sources. From the current study, it could be concluded that the PGA estimated in the regions is comparatively higher than what is reported in the codal provisions for seismic zonation and estimation of design horizontal acceleration for the region. © 2021, Springer-Verlag GmbH Germany, part of Springer Nature.Item Deterministic seismic hazard analysis of north and central Himalayas using region-specific ground motion prediction equations(Springer, 2021) Ramkrishnan, R.; Kolathayar, S.; Sitharam, T.G.Abstract: A comprehensive deterministic seismic hazard assessment (DSHA) of the north and central Himalayas (NCH) is attempted in the current study using recently developed strong-motion data-based region-specific ground motion prediction equations (GMPEs). Two source models, linear and point sources are used for hazard assessment. An updated seismotectonic map of the NCH is developed by identifying and merging the seismic sources from the Seismotectonic Atlas (SEISAT 2000) developed by the Geological Survey of India and recent literature, and a homogenized, declustered up-to-date earthquake catalogue with events since 250 BC. The NCH is divided into grids of size approximately 5 km × 5 km, and the bedrock level peak ground acceleration (PGA) at the center of each grid point is estimated using a region-specific GMPE considering both source models. The PGA values estimated at these points are exported to a GIS platform to develop a seismic hazard map of the region, separately for different sources, average and maximum of both the sources. It is observed from the current study that the PGA estimated is apparently greater than what is recommended in the codal provisions for seismic zonation and estimation of design horizontal acceleration for the NCH. Research highlights: SHA based on the state of the art DSHA technique has been carried out using various source models and recently developed region-specific GMPEs with an updated homogenized and declustered catalogue.Deterministic Seismic Hazard contour maps have been developed representing the bedrock level horizontal acceleration developed using linear and point sources.The newly developed hazard maps for the North and Central Himalayas shows higher PGA in the range of 0.4g to 0.7g towards the plate boundary region and a decreasing trend towards the peninsular shield region and the southern alluvial plains, except at the National Capital Region.The PGA estimated are comparatively higher than the design horizontal acceleration prescribed for these regions in BIS 1893. © 2021, Indian Academy of Sciences.Item Strong Motion Data Based Regional Ground Motion Prediction Equations for North East India Based on Non-Linear Regression Models(Taylor and Francis Ltd., 2022) Ramkrishnan, R.; Kolathayar, S.; Sitharam, T.G.Existing Ground Motion Prediction Equations (GMPE) in practice for North East India have been developed using limited or simulated datasets of recorded ground motions. The current study presents the development of a new GMPE based on a well-established model considering actual recorded ground motion data comprising of acceleration, magnitude, and hypocentral distances. A larger dataset with magnitudes ranging from 4.2 to 6.9 and up to 640 kms, with a total of 204 recordings is used in non-linear multiple-regression. The newly developed GMPE could predict ground acceleration realistically over larger ranges of distance and magnitudes, compared to existing GMPEs. © 2020 Taylor & Francis Group, LLC.