Abstract

When earth is excited either with surface sources, or explosive sources blasted in a shot hole, surface waves are also generated in addition to the P-wave. This surface wave travels with velocity around 300 - 600 m/sec. and having frequency around 5 Hz to 20 Hz, generally. Amplitude of surface wave is normally very large compared to the amplitude of reflected P- wave, therefore, it is necessary to suppress this wave before entering into the instrument. Since surface wave has low frequency and low velocity compared with the signal, the apparent wave number of surface wave is smaller than that of reflected P- wave. Therefore suitable spatial filter is designed which discriminates the waves according to wave numbers. This can be done in the field by designing proper arrays of sources or/and receivers, instead of a single source/receiver. Design of array depends on the characteristics of surface waves and requirement of resolution in a particular area. Parr, J.O. & Mayne W.H., Geophysics - 1955, Vol.20, (P539