Seismic array response in the presence of laterally varying thickness of the weathering layer

Abstract

Wavelet response analysis of the seismic arrays is a more convenient and direct method of analysis than using their conventional time-harmonic responses because wavelets rather than sinusoids are actually generated by the seismic source. This study comprises of the investigation of the effect of lateral variations in thickness of the weathering layer over the array length on the array response. Three types of variations are studied namely dipping bottom boundary, channel and irregular bottom boundary of the weathering layer. The parameters investigated are the number of elements (12 and 24 elements), the weighting function (equal and triangular), the incident wavelet (Ricker and Klauder), and the error amount. Root mean square (RMS) amplitude responses were more degraded in the channel case than the other two cases. Errors affected triangularly weighted arrays more than equally weighted arrays. Klauder wavelet array responses are more affected by these errors than Ricker wavelet responses. Vertically traveling waves (i.e. signals) are more affected than the horizontally traveling waves (i.e. noise). Since these variations cannot be inferred from the surface topography, these can affect the array responses without being detected unlike topographic and element's positional errors. Therefore, it is recommended to test for these effects prior to array layout. Solutions to this problem are to record single-element data and correct these during processing before summing or move the array away from these effects.