Apparent attenuation from short‐period multiples and intrinsic absorption in the seismic wavelet model

Abstract

For the purposes of predictive deconvolution one assumes that the seismic trace results from the convolution of a reflectivity series with a wavelet. A fundamental component of the seismic wavelet model is the intrinsic absorption of the earth that causes loss of high frequencies to anelastic processes during propagation. Another potentially important component of the wavelet model is the apparent attenuation caused by short-period multiples. Here we examine whether these two processes act similarly enough to be combined into a single "effective attenuation" operator for signal processing purposes. We conclude that they can be combined except in cyclic depositional environments that contain many high reflection coefficients, when the apparent attenuation operator can no longer be accurately modeled as minimum phase.

Effect of flood basalt stratigraphy on the phase of seismic waveforms recorded offshore Faroe Islands

“…Mateeva et al (2002) note that these operator properties are an exponential decay with frequency and minimum phase. They conclude that scattering attenuation is a significantly nonminimum phase in a thin layered medium with high reflectivity and a free surface.…”

“…They conclude that an effective attenuation operator would underestimate the phase-lag of the first arrivals in a medium with strong reflectivities and free surface, but it would be usable for inverse filtering without a free surface. We believe that our VSP case is more akin to the no-free-surface model of Mateeva et al (2002). The basalt layers are deep below the free surface, and the sediments above the top basalt are fairly homogeneous (not thinly layered).…”

“…The intent of predicting phase shifts with a certain Q value is to assess whether a good inverse (phase-only) Q compensation can be achieved by a Q eff at larger depths in the Brugdan I basalt sequence. Mateeva et al (2002) compare the properties of the intrinsic and scattering attenuation operators in finely layered geologies with synthetic data. They conclude that an effective attenuation operator would underestimate the phase-lag of the first arrivals in a medium with strong reflectivities and free surface, but it would be usable for inverse filtering without a free surface.…”