abstract

Rayleigh waves and P codas of CANNIKIN and shallow Aleutian earthquakes are studied in order to determine the parameters most influential in shaping the respective teleseismic amplitude spectra and in governing the surface (MS) and bodywave (mb) magnitudes. For surface-wave generation, the dipole strength (Po) of the underground nuclear explosion, and the seismic moment (Mo) of the earthquake are the important parameters. The MS for these events are comparable when Mo is approximately 3 to 4 times greater than Po. Theoretical considerations of bodywave spectra indicate that the important parameters are the permanent offset in the reduced displacement potential [ψ(∞)] of explosions and the product of area of faulting (S) and average dislocation () of earthquakes. These source parameters are related by Po = 4π(λ + 2μ) ψ(∞) and Mo = μ SD̄ where λ and μ are the elastic Lamé parameters. An additional parameter, namely, the peak frequency (fp) in the explosion P-coda spectrum and the corner frequency (fc) in the earthquake spectrum, is of paramount importance in determining the respective mb. For the events considered, fp is from 5 to 10 times greater than fc and this is manifest in the corresponding mb, where the mb for CANNIKIN is at least a unit greater than that of the earthquakes. The linear dimensions of the respective sources appear to exert a major influence upon fc and fp.

The large scatter between theoretical and actual mb values, unfortunately, precludes a firm confirmation of the above theoretical considerations.

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