An approximate method for calculating reflection and transmission coefficients for Love waves incident on a vertical discontinuity is developed. This method is applicable to any desired layered structure. The concept of a coupling coefficient between modes on either side of the boundary is introduced. This concept aids in obtaining physical insight into the problem, provided that the particle motions for the different modes are known. Several idealized discontinuities are considered and the results discussed in some detail.

Spectral analyses of seismograms of the great Chilean earthquake of May 22, 1960, from a newly installed strain seismograph at Ogdensburg, New Jersey, and from pendulum seismographs at Palisades, New York, have revealed spectral peaks corresponding to fundamental spheroidal modes 2 to 34, fundamental torsional modes 2 to 9, and the first overtone of the second spheroidal mode. Other peaks, some of which may be overtones, occur in the spectra but are not yet identified. Amplitudes of some observed spectral peaks vary radically between two time intervals on the same record. The peaks do not decrease in amplitude according to any simple law, and, rarely, an increase in amplitude with time is observed, indicating the apparent acquisition of energy in the mode between the time intervals. The periods of the graver modes of oscillation, both spheroidal and torsional, are in agreement with the theoretical values of Alterman, Jarosch, and Pekeris. The periods of the fundamental spheroidal oscillations between 250 and 500 seconds have been determined very accurately. These periods show excellent agreement with theoretical values calculated by Bolt and Dorman for a mantle with velocities according to the Gutenberg model and densities according to the Bullen model A. Also, phase velocities obtained from these periods are in agreement with Rayleigh wave phase velocities observed directly from the same earthquake by Brune, Nafe, and Alsop. Good agreement is also observed between torsional periods and theoretical values of Satô, Landisman, and Ewing, based on velocities of Jeffreys and densities of Bullen model A.

A model is proposed for the East Coast Magnetic Anomaly that, for the first time, incorporates an observed basement feature-a normal fault that consistently lies below the landward flank of the anomaly. The East Coast Magnetic Anomaly is similar to slope anomalies found over passive continental margins in many parts of the world. Thus the proposed model can be used to interpret slope anomalies in general.

The reflection and transmission coefficients for Rayleigh waves propagating from one type of wave guide to another can be computed by an approximate variational method. The method can be applied to Rayleigh waves that are normally incident on vertical discontinuities in any plane layered structure. The coefficients are computed for two‐dimensional monochromatic Rayleigh waves. The method has been used to compute reflection and transmission coefficients for two simple cases—a step discontinuity of the free surface of an otherwise homogeneous half‐space and 2 quarter‐spaces with different densities and elastic constants welded together to form a half‐space. Two‐dimensional model experiments of these cases have been performed to verify the theory. The experimental data show good agreement with the computed results as long as the structural changes at the discontinuities are not extreme.

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