An Investigation of the Earth's Free OsciIIations

Citation

Smith, Stewart Wilson (1961) An Investigation of the Earth's Free OsciIIations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/S9RW-R653. https://resolver.caltech.edu/CaltechTHESIS:04132011-081816354

Abstract

The free oscillations of the earth excited by the Chilean earthquake of 1960 have been measured by power spectral analysis of strain and pendulum seismographs. A revised and more precise table of free oscillation periods is presented. The period of the fundamental spheroidal mod _0S^0_2 is 53.82 minutes. Fine structure analysis has shown that for the first three spheroidal modes there is good agreement between the observed splitting and that calculated for a rotating earth. Results for the toroidal modes are uncertain. A theory is presented that allows recovery of some of the source properties from observations of phase differences for spheroidal modes. A comparison of theory with observation confirms original estimates of a fault length of 1000 km and a rupture velocity of between 3 and 4 km/sec. The effect of a moving source that decays exponentially with distance changes the pattern of phase shifts slightly but does not change estimates of the fault parameters. An alternative interpretation of the source properties in terms of the relative amplitudes of 2n + 1 split lines for each mode is presented but no calculations are performed. Preliminary data on the effects of geomagnetic storms on the oscillations of the earth place an upper limit of about 5 x 10^(16) ergs/cph for the energy density associated with the elastic coupling of several magnetic storms.

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