S T G Raghukanth

Standard penetration test (SPT) reveals the spatial complexity of standard penetration resistance (N-value) with depth. In this paper, a 1D stochastic characterization of spatial complexity of N-values is developed by considering data obtained from sixty two boreholes in Guwahati City. The N-value profile is modeled as the sum of deterministic part and a stochastic component. The deterministic part which characterizes the non-stationary mean of the data is determined by linear regression analysis. The remaining error is modeled as a spatial random field. The characterization of error heterogeneity as a homogeneous Gaussian random field successfully captures the observed auto-correlation function. The proposed stochastic model is used to compute the probability of factor of safety against liquefaction by Monte-Carlo simulation. The results obtained are presented in form of fragility surfaces, expressing the probability of liquefaction as a function of magnitude of the earthquake and epicentral distance. It is observed that the probability of liquefaction at Guwahati city due to strong earthquakes occurring even at large distances is very high. © 2008 World Scientific Publishing Company.

In this article, the spatial variation of ground motion in Imphal City has been estimated by the finite-fault seismological model coupled with site response analysis. The important seismic sources around Imphal City have been identified from the fault map and past seismicity data. The rock level acceleration time histories at Imphal City for the 1869 Cachar (Mw 7.5) earthquake and a hypothetical Mw 8.1 event in the Indo-Burma subduction zone have been estimated by a stochastic finite-fault model. Soil investigation data of 122 boreholes have been collected from several construction projects in Imphal City. Site response analysis has been carried out and the surface level ground motion has been determined for Imphal City for these two earthquake events. The results are presented in the form of peak ground acceleration (PGA) contour map. From the present study it has been ascertained that the maximum amplification for PGA over Imphal City is as high as 2.5. The obtained contour maps can serve as guidelines for identifying vulnerable areas and disaster mitigation in Imphal City. © Birkhäuser Verlag, Basel, 2009.

Success of earthquake resistant design practices critically depends on how accurately the future ground motion can be determined at a desired site. But very limited recorded data are available about ground motion in India for engineers to rely upon. To identify the needs of engineers, under such circumstances, in estimating ground motion time histories, this article presents a detailed review of literature on modeling and synthesis of strong ground motion data. In particular, modeling of seismic sources and earth medium, analytical and empirical Green's functions approaches for ground motion simulation, stochastic models for strong motion and ground motion relations are covered. These models can be used to generate realistic near-field and far-field ground motion in regions lacking strong motion data. Numerical examples are shown for illustration by taking Kutch earthquake-2001 as a case study. © Printed in India.