Characteristic periods and Q for oscillations of the earth following an intermediate-focus earthquake.

A set of fundamental and overtone oscillations of the earth are observed from spectral analyses of digital data recorded worldwide by the new high gain, long-period seismographs, following the Celebes Sea earthquake of 11 June 1972. The characteristic theoretical periods and the Q=Q(ω), obtained from the spectral ratio of two different time windows, are used as an aid for modal identification. The fundamental spheroidal and torsional oscillations, l=13-100 and many overtones, n=1, 2, 3, 4, and 5 are identified. The overtone oscillations with high Q of about 600 are well marked on the spectrum of Q values. The observed periods are compared to those for existing earth models and the mean of previous observations, the agreement is good. The average absolute deviations between the three theoretical and observed suites of spheroidal mode periods are between 0.710sec to 0.807sec and that of the mean period is 0.714sec. Over 50 new overtone mode of spheroidal oscillations and over 10 new overtone mode of torsional oscillations are reported.