A seismic hazard scenario in the Sikkim Himalaya from seismotectonics, spectral amplification, source parameterization, and spectral attenuation laws using strong motion seismometry

Abstract

In this paper, we present a seismic hazard map of the Indian Himalayan State of Sikkim, lying between Nepal and Bhutan Himalaya, in terms of horizontal peak ground accelerations with 10% exceedance probability over the next 50 years. These figures, the first for the region, were calculated through a stepwise process based on (1) an estimation of the maximum credible earthquake (MCE) from the seismicity of the region and Global Seismic Hazard Assessment Program considerations and (2) four seismotectonic parameters abstracted from accelerograms recorded at nine stations of the Sikkim Strong Motion Array, specifically installed for this study. The latter include (1) the frequency-dependent power law for the shear wave quality factor, Qs, (2) the site response function at each station using receiver function analysis and generalized inversion, (3) source parameterization of various events recorded by the array and application of the resulting relationships between Mo and Mw, and corner frequency, fc and Mw to simulate spectral accelerations due to higher-magnitude events corresponding to the estimated MCE, and (4) abstraction of regional as well as site specific local spectral attenuation laws at different geometrically central frequencies in low-, moderate-, and high-frequency bands. Copyright 2005 by the American Geophysical Union.