The geometrical theory of surface wave propagation on a laterally heterogeneous earth model diverges at caustics, where neighbouring rays cross. the caustics on a spherical earth are degenerate focal points at the source and its antipode; lateral heterogeneity removes this degeneracy and transforms the caustics into multiply cusped and folded curves. We investigate the geometric nature of these antipodal and source caustics using both linear ray‐perturbation theory and exact ray tracing. the regions occupied by the R1‐R2 and R2‐R3 caustics extend as far as 20° from the antipode and 30° from source, respectively, even on a relatively smooth earth model such as M84A.
|Number of pages
|Geophysical Journal International
|Published - Aug 1993
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- lateral heterogeneity
- surface waves