Seismic Reflectivity
In seismic reflection, the layers or bands observed in a seismic section are termed reflections. These reflections in the seismic data result due to contrasts in the seismic impedance (density * seismic velocity) across a geologic boundary. For a seismic wave intersecting a layer or boundary at normal incidence, the ratio of the reflected-to-incident amplitude is the acoustic impedance (R), which defines the strength or amplitude of the seismic reflection.
R = (ρ2V2 - ρ1V1) / (ρ2V2 + ρ1V1)
where, ρ is the density of the rock, V1 and V2 are seismic velocities on either side of the boundary.