Amplitude and phase corrections
Publication Date: 2014-Aug-25
The IP.com Prior Art Database
Page 01 of 4
Title: Amplitude and phase corrections
The near-surface generates a variety of problems in land data. The multiplicative effect resulting from phase shifts and strong attenuation distorts the deeper reflections. The method described here is a model-based surface-consistent solution that is also able to deal with amplitude and phase distortions related to the near-surface.
Near-surface related amplitude and phase corrections can be performed using data driven surface-consistent processing techniques (Taner and Koehler 1981; Cambois and Stoffa 1992; Garceran et al. 2013). These approaches are usually efficient for local heterogeneities, where short wavelengths are involved, while cannot be a satisfactory solution when regional heterogeneities occur.
The new method makes use of viscoelastic near-surface models (described in terms of wave-velocity and quality factor) built using information retrieved from surface and body wave propagation. This technique can solve regional anomalies.
From a kinematic point of view, seismic waves propagate according to the following equation:
where W1 and W0 are wavefield at distance r1 (reference datum) and at source point r0, respectively, c(r) is the velocity of the medium as a function of the distance and W0 can be written as:
With increasing distance from the source, the amplitudes of propagating seismic waves decay. This decay is caused by several mechanisms. In general a distinction can be made between the geometrical spreading and the attenuation of surface waves. Geometrical spreading is independent of frequency and only related to the distance the wave has travelled from the source whereas attenuation can be divided into two subcategories: intrinsic and apparent attenuation (Liner, 2012). The amplitude decay of a propagating seismic wave is given by:
where the function G( ) represents the geometrical spreading, and are the intrinsic and apparent attenuation with their respective attenuation coefficients α. Apparent attenuation is caused by scattering or by layer-related phenomena such as reflection, transmission, etc. and conserves energy. It results, however, in a loss of amplitude, which is dependent of the wavelength and the frequency (Liner, 2012). Intrinsic attenuation, on the other hand, is the irrecoverable loss or conversion of wave energy into heat and is a material property. In the frequency range, which is used in surface-seismic data, the intrinsic attenuation is relatively constant and generally small (Liner, 2012).
The attenuation of seismic waves is also intrinsically related to dispersion (Aki & Richards, 2002). Without this relation, all attenuation models would lack causality. This dispersion is also called intrinsic dispersion and is negligible for some applications since even for highly attenuating media the velocity variation as a function of frequency is very small (Ursin & Toverud, 2002).
Analyzing surface and body...