Acquisition and processing of pure and converted shear waves generated by compressional wave sources

Abstract

The most common source of seismic energy onshore is a vertical impact on the earth's surface or an explosion at some depth in a borehole. These sources produce mainly compressional waves. Here it is shown how these sources can be used to generate shear waves either by conversion in the depth or in the immediate vicinity of the source itself. The use of theoretical seismograms can help to identify the individual onsets especially on the horizontal components of the earth's movement. Due to the more complex raypath, converted waves need a special data processing. The spectral behaviour can be improved by spectral balancing followed by a spiking deconvolution. As the CDP-concept is no longer applicable for converted PS-waves a special sorting for a common conversion point (CCP) is applied. The identification and analysis of the individual waves can be simplified by a detailed polarization analysis taking into account the full dynamic behaviour of the observed waves. Prestack depthmigration of converted PS waves allows to deduce additional information on the material properties of reflecting horizons. The depth-migration of individual shot gathers is achieved in the frequency-space domain. Thus the kinematic and dynamic aspects of these secondary waves is a valuable tool for a better understanding of the elastic behaviour of the subsurface.