Seismic site characterization in northeast India: a holistic GIS based approach

Abstract

The seismic site effect is critical in designing structures and the estimation of earthquake damage to existing structures, particularly in seismically active regions. To assess site-specific earthquake risks and design earthquake-resistant structures, it is necessary to classify a site according to its class. Here, the seismic site characterization (SSC) attributes have been generated using a topography gradient-based approach as the geophysical and geotechnical attributes are limited and insufficient for regional site classification in Northeast India. We attempted to quantify the dynamic properties of subsurface materials in terms of time average shear wave velocity (Vs30), frequency-dependent amplification factor (Af), predominant period (Ts), and vulnerability index (Kg). Subsequently, a holistic GIS model has been developed to classify the region into three microzones, viz. Low Susceptible, Moderate Susceptible, and High Susceptible by the integration of all the SSC attributes. The generic site response curve for various SSC zones has been developed through Horizontal-to-Vertical Spectral Ratio (HVSR) analysis of recorded strong ground motion. The present results show that SSC attributes corroborated with the geological, tectonic, geomorphological, and topographic settings of Northeast India. It is exhibited that the site classes E, D1, D2, and D3 are mostly associated with the Lower Brahmaputra Basin. The weak zone that failed during the earthquake in the basin areas has also been identified based on the highest Kg value (>10). This study has resulted in a map of seismically vulnerable regions. The developed SSC maps and generic site response curves may be used for surface consistent ground motion synthesis, seismic microzonation, risk mapping, and in developing earthquake mitigation strategies in Northeast India.

Keywords

• vs30
• site class
• hvsr
• site response
• vulnerability index (kg)
• northeast india