Improved resolution of reflections from the crystalline upper crust

Summary. Use of higher frequencies and a careful selection of the other data acquisition parameters can significantly enhance the resolution obtained in reflection seismic CDP profiling in hard rock terranes. Experiments with a 20–80 Hz non-linear vibroseis sweep near the projected ADCOH site reveal that the wave-field reflected from the upper crust contains frequencies spanning the entire source spectrum even in the presence of a weathered layer of saprolite. Attenuation of higher frequencies and the severe distortion produced by the 'notch' filter for line-frequency necessitate some pre-processing spectral shaping. The operations are linear and yield, as a by-product, an estimate of the average 'Q' for the section - about 250 in the present case.