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Overtone modes of free oscillation of the Earth have been observed with two instruments at two separate locations after the Colombian earthquake of July 31, 1970. Certain overtones persisted with a signal-to-noise ratio as high as 20 db for 50 hr after the origin time. Some spheroidal radial overtones (modes of type nS0) were found to have Q's near 1000, about three times the typical Q of a fundamental mode (0Sl). Multiplet centre frequencies and Q's were measured for several overtones, with good agreement between the two stations.
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Dratler et al. (1971) studied this question.
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