OPTIMIZATION OF WIDE-ANGLE SEISMIC SIGNAL-TO-NOISE RATIOS AND P-WAVE TRANSMISSION IN KENYA

In previous refraction and wide-angle reflection experiments in the Ke nya Rift there were problems with poor signal-noise ratios which made good seismic interpretation difficult. Careful planning and preparatio n for KRISP 90 has substantially overcome these problems and produced excellent seismic sections in a difficult environment. Noise levels we re minimized by working, as far as possible, at times of the day when conditions were quiet, while source signals were optimized by using di spersed charges in water where it was available and waterfilled boreho les in most cases where it was not. Seismic coupling at optimum depth in water has been found to be more than 100 times greater than it is i n a borehole in dry loosely compacted material. Allowing for the sourc e coupling, a very marked difference has been found between the observ ation ranges in the rift and those on the flanks, where the observatio n ranges are greater. These appear to indicate a significant differenc e in seismic transmission through the two types of crust.