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Wavelet filter analysis of atmospheric pressure effects in the long-period seismic mode band |
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| Authors: | X-G Hu L-T Liu HT Hsu |
| Institution: | a Institute of Geodesy and Geophysics, Chinese Academy of Sciences, 340 Xudong Street, Wuhan, China b Graduate School of Chinese Academy of Sciences, Beijing, China c Institut de Physique du Globe de Strasbourg (UMR 7516 CNRS-ULP), 5 rue Descartes, 67084 Strasbourg Cedex, France |
| Abstract: | The importance of the reduction of atmospheric pressure effects becomes very clear when investigating seismic normal-mode spectra below 1.5 mHz. The usual simple correction method consists in subtracting a term converted from local atmospheric pressure (pressure multiplied by a frequency-independent admittance) from the gravity record in time domain. Thus, estimating an efficient admittance is the key for an improved correction. Band-pass filters derived from dyadic orthogonal wavelet transform, having narrow pass-bands with good frequency response but without Gibbs phenomenon and causing no phase lag, are very helpful to estimate an efficient admittance, which is both time and frequency-dependent. Processing of high quality superconducting gravimeter (SG) records for the great Sumatra earthquake (Mw = 9.3, Dec 26, 2004) with wavelet filters reveal the three very well resolved splitting singlets of overtone 2S1 with a single gravity record after correction with time-dependent and frequency-dependent admittances. We also observe all coupled toroidal modes below 1.5 mHz, except 0T5, 0T7 and 1T1, with good signal-to-noise ratio (SNR); moreover, toroidal modes 1T2 and 1T3 are for the first time unambiguously revealed in vertical components. |
| Keywords: | Wavelet filter Pressure correction Free oscillations Superconducting gravimeter |
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