A shallow seismic refraction survey to map the velocity lithology relationship of the weathred and subweathered layers

Abstract

A seismic refraction survey was carried out in Tarlai Khurd a village of Islamabad to map the weathered and subweathered layers 'and to establ ish their velocity litho logy relationship. Six refraction profiles covering SfJo cj')'. -rn of area were laid in the area and cove r ed by reverse shooting. The parameters such as true velocities, depth and dip angle of the refractor were obtained on Hewlett Packard Model-216 personal computer. The results have been presented in the form of Iso-velocities (Vo,V1) , Iso-dip and Iso-Pach (Ho) maps. The velocity in the mapped weathered layer ranges from 320- 540 mls and in subweathered layer from 1600- 2270 m/s . The depth of weathered and subweathered layers varies from 5.1-10 meteres and 11.5-21.4 meteres respectively. The weathered layer may comprise of clay, silt and shale while sub-weathered layer may comprise of friable sandstone with clayey and shaley intencalations and 'at places may be moisture impregnated.