NEAR‐SOURCE PULSE PROPAGATION: APPLICATION TO Q‐DETERMINATION1

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Abstract
Among the approaches generally used to measure attenuation from field data, the study of the first pulse broadening appears to be one of the more promising methods to estimate the quality factor Q for different geological formations including soils. Using a numerical scheme, we studied the evolution of the pulse shape in the neighbourhood of the source in order to establish the limits of the method. It was found that the pulse width variations depend strongly upon source depth. At short distances from the source, the pulse shape is controlled mainly by the near‐field terms and/or the onset of surface waves. The investigations proved that the pulse‐broadening method is reliable for distances greater than about 1.2 wavelengths. From numerical experiments, the maximum error in Q‐determination is found to be 10% in the half‐space case.