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Published March 10, 1975 | Published
Journal Article Open

Amplitude of the Earth's free oscillations and long-period characteristics of the earthquake source


Amplitude spectra of the spheroidal modes _0S_l(l = 2–40) excited by the 1960 Chilean earthquake and observed at Pasadena, Los Angeles, and Isabella show distinct holes at 0_S_(10) (T = 580 s) and _0S_(21) (T = 336 s). These holes can be explained as an interference pattern caused by a composite source consisting of a finite propagating source (main shock) and a slow precursory source, 15 min before the main shock. A total seismic moment of 4–5 × 10^(30) dyn cm is required to explain the observed amplitude.

Additional Information

© 1975 by the American Geophysical Union. Received August 22, 1974; revised October 29, 1974; accepted November 14, 1974. We thank Louis B. Slichter and Stewart W. Smith for kindly providing us with the digitized records of the Chilean earthquake. Christopher Harrison, Francis Lehner, and Len Blayney provided us with useful information for the calibration of the instruments. We also thank the reviewers of this paper for constructive comments. This work was supported by National Science Foundation grant GA 40752 and Advanced Research Projects Agency grant F44620-72-C-0078. Contribution 2521, Division of Geological and Planetary Sciences, California Institute of Technology.

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