ASSESSMENT OF STRONG GROUND MOTION FOR SHILLONG PLATEAU REGION

Abstract

The sharp increase in population and urbanization, and absence of proper earthquake resistant measure have led to alarming increase in vulnerability of Shillong Plateau region to damaging earthquakes. Therefore, there is an urgent need to analyze vulnerability of this region to the damaging earthquakes, and in the absence of availability of sufficient strong motion recordings from the region, the strong ground motion is needed to be estimated utilizing the database of seismicity, tectonics, geology and the appropriate ground motion attenuation relation for the region so that it can help to take proper measure. and to be prepared against the disastrous effect of future earthquakes. The main objective of the study is estimation of ground motion using two different approaches. The first approach is to estimate the strong ground motion by taking into account the effect of various seismotectonic sources in the study area, and second approach is to estimate strong ground motion produced by the Shillong Plateau Earthquake of 1897 based on intensity data. In this study, for estimation of ground motion Abrahamson-Litehiser (1989) relation and Boore-Atkinson (2008) have been used. Using the method proposed by Gasperini et al. (1999) the source parameters of 1897 Shillong earthquake are estimated and Murphy and O'Brian (1977) relation is used to calculate the intensity based ground motion in terms of PGA(g). The results of ground motion estimation using empirical relations by deterministic approach are presented in the form of zones of PGA(g) distribution over the Shillong Plateau. Further, zones of 5% damped spectral accelerations for 0.2 s and 1.0 s natural periods are also presented. The source parameters of 1897 Shillong earthquake are estimated and intensity based ground motion in terms of PGA(g) is calculated and presented in the form of interpolated zones over the Shillong Plateau region