Abstract
We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.
Highlights
Interpretation of seismic data is often made tedious, and sometimes erroneous, because the seismic records contain primary events from the subsurface interfaces and spurious secondary events which interfere with the desired signals
This consistent variation agrees with the statistical test of randomness [4,10] that if the numbers are truly random, the sum of K random traces will be proportional to K1 2, so that the signal-to-noise ratio (SNR) will be improved by K1 2
The automatic procedure for the processing of lowquality seismic refraction data presented in this work include automatic determination of layer velocities and the corresponding intercept time which are used to compute other layer parameters
Summary
Interpretation of seismic data is often made tedious, and sometimes erroneous, because the seismic records contain primary events (or signal) from the subsurface interfaces and spurious secondary events (or noise) which interfere with the desired signals. The common causes of seismic noise are surface waves and near-surface waves ( Rayleigh waves) initiated by source pulses, multiple reflections between the surface and geologic interface, near-surface in-homogeneities such as pebbles, boulders, root of trees and other non-uniformity that can cause scattering of seismic waves locally. Such diverse types and varying frequencies of noise resulting from diverse sources require different approaches to remove or minimize their impacts on seismic interpretations. Because each spread requires several hammer blows at the shot point, the method has the disadvantage of being slow with required increase labour and extra cost of purchasing additional component, the SAS machine
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