Understanding the structure of deeper parts of the earth of vital improtance to understand the relationship between the processes thant the have taken place inside it and evolution of various structural/ tectonic features present on the Earth's surface.This knowledge also provides insight into the characteristics of the earthquakers,other natural hazards and formation/distribution of the natural resources.The geological efforts to study the Earth,including drilling,are limited to its top few hundred meters but have provided comprehensive knowledge on the material that is of direct socio-economic interest to the human being.