RESHAPING SPECTRUM ESTIMATES BY REMOVING PERIODIC NOISE - APPLICATIONTO SEISMIC SPECTRAL RATIOS

An automated method for removing line spectrum elements embedded in co lored spectra is presented. Since smooth spectrum estimates are desire d, line spectra tend to smear out over an effective smoothing window. This introduces a bias in spectrum estimation that seriously degrades signal-to-noise ratios, spectral deconvolution or any other operation where spectrum shape is important. Multitaper analysis provides a simp le algorithmic solution including a method of determining where spectr al peaks are both significant with high power. The method is completel y general, and examples include estimation of signal-to-noise ratio at the 1990 high frequency array, Pinyon Flat, CA. A comparison of noise spectra line segments and signal spectra line spectra reveals similar ities associates with instrument noise ans shallow resonances stimulat ed by incoming seismic signals. Identification and removal of resonanc es can provide a better means of estimating background noise spectra f or modeling earthquake source spectra and path effects associated with attenuation.