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Filtering of a Ricker wavelet induced by anelastic seismic wave propagation and reflection

Abstract : A varying Q factor with depth induces modifications of seismic wave features due to anelastic propagation but also reflections at the discontinuities. Standard signal analysis methods often neglect the reflection contribution when assessing Q values from seismic data. We have developed an analytical quantification of the cumulative effects of both the propagation and reflection contributions by considering Kjartansson's model and a seismic plane wave at normal incidence on a step-like discontinuity. We show that the cumulative effects are equivalent to a frequency filter characterised by a bandform and phase that both depend on the ratio between the elastic and anelastic contrasts. When considering this filter applied to a Ricker wavelet, we establish an analytical expression of the peak-frequency attribute as a function of propagation and reflection properties. We demonstrate that this seismic attribute depends on the anelastic contrast, which cannot be neglected when assessing Q factors: the error in Q estimate is not linearly dependent on the anelastic contrast and we establish an analytical expression for the case where this contrast is weak. An unexpected phenomenon for a step-like interface is an increase in the peak frequency that is observed when the anelastic and elastic contrasts have opposite signs, with a constraint on the anelastic propagation properties. This behaviour allows for assessment of the elastic and anelastic parameters.
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Submitted on : Thursday, November 5, 2020 - 11:57:22 AM
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Stephan Ker, Yves Le Gonidec. Filtering of a Ricker wavelet induced by anelastic seismic wave propagation and reflection. Journal of Geophysics and Engineering, IOP Publishing, 2020, 17 (5), pp.838-851. ⟨10.1093/jge/gxaa033⟩. ⟨hal-02989177⟩

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