Faculty Publications
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Item Influence of tectonic regime in the selection of ground motions for seismic site response analysis(International Association for Earthquake Engineering, 2021) Shreyasvi, C.; Chopra, S.; Venkataramana, K.The common practice in seismic site response simulation is to use the ground motion records consistent with the tectonic regime. In other words, for sites located in a stable continental region, ground motions recorded in a region with the same tectonic setup is used in computing the site response. In the present study, an attempt has been made to test the applicability of different ground motions in the simulation of local site response for a stable continental region. The numerical study was performed by using 140 ground motions recorded in stable continental areas and 150 ground motions recorded in active areas. The earthquake events with magnitude in the range of MW 5-8 and distance 1-300km (active) and 1-500km (stable) were chosen. The magnitude range was further categorized into various magnitude bins with a variation of 0.5 and distance bins with a variation of 50km. The ground motions were selected in such a way that there exist at least 5-7 ground motions in each combination of the magnitude and the distance bin and recorded at a site with VS > 760ms-1. The soil profile was chosen from Gandhinagar, Gujarat, Western India, which is an intraplate region. The seismic site response of this site was studied in the form of predominant period and the amplification. The variation of these parameters in different scenarios was evaluated. The spectral amplification observed for ground motions from both the tectonic regimes has been compared. The results reveal that the predominant frequency of the soil deposit varies between 0.3-0.4s depending on the induced strain by the input motion. Also, the difference in the performance of the soil deposits to the ground motions is evident in the amplitude. Overall, the present study is an attempt to address the merits and demerits of using ground motions of the active tectonic regime in a stable continental region. © The 17th World Conference on Earthquake Engineering.Item Estimation of Local Site Effects in Indian Scenario: Lessons from Past Earthquakes, Current Practices, and Future Trends(Springer Science and Business Media Deutschland GmbH, 2022) Shreyasvi, C.; Venkataramana, K.The incorporation of local site effects in seismic hazard analysis has evolved radically over the last few decades. Initially, the whole site characterization was expressed by a single scalar quantity known as soil factor. The advancement in technology has paved the way for more sophisticated techniques in estimating the site response. The new-age techniques of site characterization involve field investigation as well as laboratory testing of the soil samples. The study sites are modeled in more than one dimension, and the complex phenomena of site response such as basin effects and resonance in a valley are computationally simulated. The present article outlines the state-of-the-art practices in characterizing site/soil response to tectonically induced ground shaking. The article briefs about the different methods and provides a detailed description of the computational methods for estimating the site response. The existing methodologies, their applicability, and pitfalls are presented. Additionally, the scope for future work and the direction toward improving the existing methods have been discussed. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Nonlinear Soil Amplification Models for a Moderately Active Seismic Zone in India(Springer Science and Business Media Deutschland GmbH, 2021) Shreyasvi, C.; Venkataramana, K.The dynamic stiffness and damping of the soil material, depth of the soil profile, impedance between the soil and the underlying bedrock and soil nonlinearity are the factors influencing the local site response. The important parameter in assessing the site response is the “amplification factor,†which is usually correlated to Shear Wave velocity in the top 30 m (Vs(30)). Though using VS(30) as an index for amplification is simple and robust, it is not recommended for site-specific applications. In the present study, two distinct soil types i.e. “Sand†and “Clay†with the same value of VS(30) demonstrated variable amplification characteristics. Hence, distinct site amplification models were derived for the two soil types considering the intensity of the input bedrock motion as the primary independent variable. The borehole data from nearly 50 locations in North Kerala, an intraplate region in the Southern part of India was collected. The ground response was simulated in 1-dimension considering equivalent linear behavior of soils on the SHAKE 2000 platform. The ground motions used in the simulation were scaled to the target spectrum obtained from the regional seismic hazard assessment. The average spectral amplification observed is 5 for “Clay†and 3.5 for “Sand†in the study region. The soil profiles categorized as “sand†exhibits nonlinear behavior. “Clay†deposits reveal sustained amplification at longer periods and hence, can significantly influence ground response during longer duration ground shaking. The empirical amplification equations developed from the study can be used to modify the generic ground motion prediction models to region-specific applications. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.