Seismic survey for delineation of shallow structures in the 2001 earthquake - Affected areas Anjar and Bhuj, Gujarat

Shallow seismic refraction survey (Hammer source) was carried out by Geological Survey of India in Kutch district Gujarat after the devastating i.e. earthquake of 26(th) January 2001. The aim of the investigation was to delineate different lithological units based on their P-wave velocities in earthquake-affected areas of Anjar and Bhuj. The seismic survey carried out over 17 locations in township areas of Anjar and Bhuj has reflected two to three layer structures. In both areas, the P-wave velocity of first layer varies from 476 m/s to 1067 m/s while the velocity of second layer varies from 1091 m/s to 1892 m/s. The third layer exhibits the velocity ranging, from 1818 m/s to 4865 m/s. The first layer corresponds to loose soil; second layer to compact soil/weathered rock and third layer to weathered/bedrock. The depths given by two boreholes drilled in both areas of study are in excellent agreement with those obtained by seismic survey conducted at borehole locations. This lends additional credence to geophysical results obtained in the area. According to layer parameters deduced from shallow seismic survey, the foundation of houses in earthquake-affected areas should be below first interface/or in second layer i.e. compact soil/weathered rock to be safer.