In this work, we are concerned with aspects of seismic data that show frequency dependence. It is at the outset unnecessary to justify this study because those involved in acquisition, processing, and interpretation of seismic data are faced with strong frequency dependence every day. At first impression, the topic seems self-evident: "Of course everything is frequency dependent." However, consider the vast theoretical edifice of acoustic and elastic wave propagation erected since the 1860s. Wave speeds, reflection coefficients (and therefore AVO), geometric decay, Snell's law, and many other topics typically are presented as being independent of frequency.
If we think of classical unbounded wave propagation, there can be frequencydependent attenuation in the surface-seismic frequency band below 100 Hz, but that intrinsic attenuation is weak in elastic rocks and is only slightly stronger in poroelastic media. Typically, that intrinsic attenuation is vastly overshadowed by apparent attenuation caused by layering and near-surface irregularities. Both intrinsic and apparent attenuation depend on frequency, but the former is a rock property measurable in the laboratory, whereas the latter is a frequency-dependent field whose characteristics emerge only when long waves travel through a layered earth.