This figure shows the time interval, in seconds, between the arrival of the P and S phases, as a function of epicentral distance. This plot is made for an earthquake at the surface, that is, with 0 km source depth. For a deeper earthquake, the elapsed time between the P and S phases would be slightly smaller.
This page is URL:
http://aslwww.usgs.gov/Education/s-p_curv.html/
Last modified on July, 1998 (rlw)