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Maine seismic experiment: Frequency spectra of refraction arrivals and the nature of the Mohorovii discontinuity

APPLIED SCIENCE LABORATORY GENERAL DYNAMICS/FORT WORTH, FORT WORTH, TEXAS
DEPARTMENT OF GEOLOGY AND GEOPHYSICS THE PENNSYLVANIA STATE UNIVERSITY, UNIVERSITY PARK, PA.

Abstract

Wave forms of first arrivals at various distances from explosions in the Gulf of Maine, 1961, were analyzed by Fourier integral analysis. Frequency spectra of the wave forms in the frequency range 2.6 to 25 cps were obtained. The frequency spectra of the refraction arrivals were compared with those of the direct arrivals. Statistical tests show that there is no clear dependence of the frequency content of the arrivals upon distance for either the direct or the refraction arrival, and that the two groups of arrivals definitely belong to two separate groups. Comparison with the results of a model experiment enables an estimate of the minimum possible velocity gradient at the Mohorovii discontinuity to be made. On the assumption of a linear velocity transition at the boundary, the minimum possible velocity gradient is found to be 4 (km/sec)/km, or the maximum possible thickness of the transition layer to be kilometers.

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				D. E. SISKIND and B. F. HOWELL JR< Scale-model study of refraction arrivals in a three-layered structure Bulletin of the Seismological Society of America, June 1, 1967; 57(3): 437 - 442. [Abstract] [PDF]

				B. F. HOWELL Jr. and T. G. BAYBROOK Scale-model study of refraction along an irregular interface Bulletin of the Seismological Society of America, June 1, 1967; 57(3): 443 - 446. [Abstract] [PDF]