Site Amplification, Qs, and Source Parameterization in Guwahati Region from Seismic and Geotechnical Analysis

Abstract

As devastating earthquakes continue to inflict widespread destruction to life and property and hinder the development of urban areas, the technical and scientific problems of seismic hazard assessment and risk-related issues warrant urgent attention. In this regard, seismologists play a key role in defining the source parameters of earthquakes and estimating the associated site-specific ground motion amplification commonly termed site response. The relevant analyses are usually performed using either recorded ground motion for a handful of seismic events of moderate to large magnitude or by synthesizing stochastic processes based on the observational data. The hazard projection is aimed at a great earthquake or a maximum earthquake or maximum credible earthquake on probabilistically/deterministically defined terms for a seismic zone under investigation. Seismic sources generally are characterized by well-defined physical parameters such as corner frequency f c , seismic moment M , and stress drop Δσ, derived directly from waveform data, i.e. , strong ground motion records for events with significant magnitude. On the other hand, site amplification of ground motion is attributed to either the geomorphological features that produce scattering, focusing, or defocusing of incident energy or thick alluvium-filled terrain that causes reverberations due to trapped energy. The potentially severe consequences of this phenomenon have been demonstrated in the damage patterns of several earthquakes, such as the 1985 Michoacan, Mexico, earthquake (Singh et al. 1988), the 1988 Armenian earthquake (Borcherdt et al. 1989), and the 1989 Loma Prieta earthquake (Hough et al. 1990; Borcherdt and Glassmoyer 1992). Another aspect of ground motion analysis or synthesis is the attenuation of seismic waves along the propagation path connecting the earthquake source and the recording site (observatory). The attenuation may be attributed to degradation in the elastic properties such as shear and compressional moduli and the scattering of seismic waves caused …