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Refraction seismographs are usually wide-band instruments and so it is relatively easy to make meaningful amplitude measurements. It is shown how to correct for normal instrumental variations, for variations in charge weight, for geophone ‘plant,’ and for geometrical loss due to enlargement of the wavefront. After these corrections have been made the residual amplitudes are controlled mainly by the properties of the refractor.

The residual attenuation falls roughly into three groups. These have means of a few hundredths of a decibel per wavelength, a few tenths of a decibel per wavelength, and a few decibels per wavelength. The first group is indicative of a thick nonporous refractor; the second group is indicative of a thick porous refractor; and the third group indicates a thin refractor.

Examples are given which illustrate the use of amplitudes to determine critical distance, to distinguish between a discretely layered and a continuous velocity distribution, and to decide which of several possible time-distance interpretations is correct.

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