Open AccessFEATURES OF SEISMIC pP AND PP RAYS
Author(s) -
Bullen K. E.
Publication year - 1955
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1955.tb00379.x
Subject(s) - cusp (singularity) , discontinuity (linguistics) , focus (optics) , geology , mantle (geology) , geometry , geophysics , physics , geodesy , mathematical analysis , mathematics , optics
Summary Previous theoretical work on features of seismic rays has been extended to the case of p P and PP rays. It is shown that, for a wide class of velocity variations in the Earth's outer mantle, there is a cusp in the p P travel‐time curve which corresponds to a ray which leaves a focus at finite depth in a direction inclined at a finite angle above the horizontal through the focus. It is also shown that the cusp is in general theoretically similar to the cusp in the PKP case. A method is given for locating this cusp for particular focal depths and is illustrated in an application to the Jeffreys‐Bullen travel‐time data. The general influence of the 20° discontinuity is discussed. Comment is made on conventions in naming p P and PP rays.