SEISMIC WAVE ATTENUATION IN NONRESOLVABLE CYCLIC STRATIFICATION

Abstract

Situations arise in seismic exploration in which thick zones generate no well‐defined reflection events even though the sonic logs exhibit significant velocity stratification. In many cases, reflections are not generated because the stratification is so fine that it cannot be resolved by the seismic frequency band. Nonresolvable sections in which the impedance structure is cyclic in character, such as sand‐shale sequences, are shown to exhibit frequency dependent attenuation which differs from the linear dependence commonly attributed to absorption. This difference may be exploited to separate the absorptive and stratigraphic components of attenuation and to compare their relative magnitudes. Only in depth intervals in which the reflection coefficients are unusually large can stratigraphic attenuation account for observed attenuation of the order of a few tenths of a decibel per hundred feet. Relations are derived for determining the effect on the stratigraphic attenuation of scaling the parameters which characterize the section.