Open AccessCaustics in seismology
Author(s) -
Nye J. F.
Publication year - 1985
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1985.tb06498.x
Subject(s) - caustic (mathematics) , mantle (geology) , geology , antipodal point , diffraction , eikonal equation , core–mantle boundary , geophysics , geometry , physics , optics , mathematics , quantum mechanics
Summary. Catastrophe optics provides insights into the structure of the caustics produced by seismic events. Two examples are given. The first is the caustic formed on the surface of the Earth between 10° and 30° from the event by P rays that have reached the transition zone of the mantle. This is organized by one or more approximately circular cusp lines; these are generally below the surface, but because of lateral (regional) variations, they are puckered. Where they intersect the surface they give rise to characteristic beak‐to‐beak and lips patterns. The second example is the caustic structure produced by refraction at the core–mantle boundary. There is a four‐cusped figure at the antipodal point, and, in addition, it is suggested that the main 143° PKP caustic is actually cusped, the cusps being smeared out when radially symmetric earth models are used. The cusps arise from bumps on the core–mantle boundary. In general, the caustic, and its accompanying diffraction structure, associated with a bump can be understood as an unfolding of the parabolic umbilic catastrophe.