Comparison of least squares analyses of long and short period P wave amplitudes

A least squares technique used previously in analyses of the amplitudes of short period P waves has now been applied to observations of P waves recorded on long period instruments. Intercomparison of all the results obtained by this method indicates that the true amplitude distance curve is less irregular than the one derived by Gutenberg and Richter, and in particular that there is no large peak in amplitude between 35° and 45°. There is some suggestion of small scale irregularities in the curve, which it should be possible to define more clearly by analysis of a greater quantity of data. The range of variation of station amplitude corrections is much the same for long and short period waves, which suggests that the variations result from regional differences in the structure of the upper mantle. The rates of attenuation beyond about 80° for waves of different periods are approximately in conformity with those predicted from theoretical studies by Phinney and Cathles of diffraction effects at the core-mantle boundary. However, no certain inference can be made about the velocity structure at the base of the mantle from the results presently available.