SYNTHETIC SEISMOGRAMS AT NON-VERTICAL INCIDENCE

Synthetic seismograms are usually computed for reflections from vertical incidence of P waves for a horizontally layered medium. In actual practice the angle of incidence departs from the vertical, as receivers are usually located at some distance from the source. At angles other than the vertical, the conversion of P‐ to S‐wave energy and changes in the reflection coefficient affect the shape of the synthetic seismograms. The effect of non‐vertical incidence on synthetic seismograms is examined in this paper. Seismograms at non‐vertical incidence have been computed using the plane‐wave approach of Haskell (1953) for a layered medium. The use of plane waves is an approximation to the actual case of spherical wavefronts from a surface source. Using plane‐wave theory, the expected wave forms as a function of angle of incidence were computed numerically for several simple models. The results indicate that the synthetic seismograms do not change significantly for angles of incidence between o and 25 degrees. For larger angles the changes in the wave forms may be severe. The effect is more pronounced for high‐velocity layers than for low‐velocity layers. Copyright © 1979, Wiley Blackwell. All rights reserved