Acquisition and Analysis of Surface Wave Data in the Indo Gangetic Basin

Abstract

Seismic activity in the tectonically active Himalayan region can result in devastation in the contagious deep Indo-Gangetic Basin (IGB). It is filled by alluvial deposits and, therefore, prone to site amplification. IGB had experienced catastrophic earthquake damages due to the presence of thick soil depth of 0.05 km to about 4 km. However, very few studies have presented seismic site characterization of the IGB soil up to the shallow depth, and very limited attempts have been made to measure the dynamic properties of the deep soil column. Hence, in this study, shear velocity profile ($$ {\mathbf{V}}_{{\mathbf{s}}} $$ ) up to 400 m depth is measured using combined active and passive multichannel analysis of surface wave (MASW) survey in 275 selected locations in IGB. Acquisition and processing of the seismic surface wave data to obtain the $$ {\mathbf{V}}_{{\mathbf{s}}} $$ profiles at shallow and deep depths are discussed in this paper. Parametric study has been done to identify the variation in dispersion and $$ {\mathbf{V}}_{{\mathbf{s}}} $$ profiles by recording time, different sampling interval, different polarity and gain. It has been seen that changing any parameter during data recording may result in variation in $$ {\mathbf{V}}_{{\mathbf{s}}} $$. Further, the surveyed sites are classified and characterized based on time-averaged $$ {\mathbf{V}}_{{\mathbf{s}}} $$ in the upper 30 m depth as per National Earthquake Hazards Reduction Program seismic site classification. $$ {\mathbf{V}}_{{{\mathbf{s}}30}} $$ values vary from 157 to 1152 m/s in the entire stretch of IGB. This is the first time such extensive study was carried out in IGB for $$ {\mathbf{V}}_{{\mathbf{s}}} $$ determination at deep and shallow depths.