|Author(s)||Ker Stephan1, Le Gonidec Yves2|
|Affiliation(s)||1 : IFREMER, GéosciencesMarines, Centre de Brest, 29280 Plouzané, France
2 : Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France
|Source||Journal of Geophysics and Engineering (1742-2140) (Oxford), 2020-10 , Vol. 17 , N. 5 , P. 838-851|
|Keyword(s)||seismic attenuation, Q factor, anelasticity, seismic data analysis|
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 the 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 characterized 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 assessing the elastic and anelastic parameters.
Ker Stephan, Le Gonidec Yves (2020). Filtering of a Ricker wavelet induced by anelastic seismic wave propagation and reflection. Journal of Geophysics and Engineering, 17(5), 838-851. Publisher's official version : https://doi.org/10.1093/jge/gxaa033 , Open Access version : https://archimer.ifremer.fr/doc/00640/75240/