Earth-model discrimination method

Summary) Investigation of the earth's interior is attempted via gravimetric terrestrial spectroscopy from superconducting gravimeter (SG) records containing all medium and large earthquakes that affected the SG. I introduce a general (single station, all-type earthquakes; no preor post-processing) method that enables discrimination amongst geophysical earth models by establishing if and when there exist high direct functional correlation values between the oscillations of the earth gravity field taken at a model's low eigenfrequencies, and the earth seismicity expressed in seismic energies and seismic magnitudes. I demonstrate for the first time in geophysics the negative effect that the generating of input-data, for the purpose of completing the time-series, has on the Fourier spectral analyses. To accommodate the problem on existing computers and to create nondistorted 8-sec and 32-sec filtered records from the original one-second data, I design a non-equidistant filter that applies Gaussian weights while accounting for missing data within the filtering step. So filtered, the records are then used in computing the least-squares spectra. Earthquakes are the most common source of abrupt releases of kinetic energy on earth. I then exploit the Jeffreys's rule of thumb: in many earthquakes observations of only the horizontal earth movements during the passage of shear (S) waves cart be ccsed to estimate the order of the total released energy. From here I infer that the ratios of kinetic energy E K traveling throughout the earth and displacing the inner masses, vs. seismic energy E S as that part of kinetic energy, which is transmitted mostly through the lithosphere in the form of surface-waves and measured by the seismographs, ought to bc constant in most earthquakes. I then hypothesize that the measure of the earth gravity field oscillations, as deduced in the form of median magnitudes of gravity spectra, stands in a direct correlation with earth seismicity along the low characteristic frequencies. In order to prove the hypothesis I process some 10.1 billion observations and compute the diurnal averages of non-reduced-gravity oscillation magnitudes for the last decade and for each long normal mode for three different earth models. I then directly correlate three series against the series containing seismic energies, as well as agamst the series containing seismic magnitudes of 381, M > 6.3 earthquakes for each day in the [-30, +30] days interval. Direct cross-correlation values as high as 0.97 were obtained, and the hypothesis thus proven. The direct functional correlation values between diurnal average magnitudes of the earth gravity field and all medium-to-large earthquakes from one decade are proposed as a tool for discriminatmg amongst earth models. If high functional correlation values can be obtained using this method, a tested earth model is to be considered a successful one. The functional correlation values computed from variance-spectra are shown to possess an absolute high for periods of ∼821 s, which could be used as a refinement constraint in earth-model design. For all three earth models the functional correlation values are higher when seismic energies are used rather than seismic magnitudes, as well as when variance-spectra are used rather than power-spectra. » Purchase the full text Dissertations and theses can be purchased in a variety of formats which may include: PDF for web download, softcover, hardcover, or microform. Click the "Order a Copy" button to see the formats available for this item.