GATE-2018 (24) :Wyllie – Time average equation

 SEISMIC METHOD

1. Critical distance x_crit is where refracted phase is first observed.

2. Cross-over distance x_cros is where the travel times of the direct and refracted arrival are equal.

 

3.The refracted waves propagate in the deeper, faster medium, just below the material interface. Normally the first phases to arrive at a receiver, these are called head waves



Reference:  http://www.earth.ox.ac.uk/~karins/tmp/Lectures7-8_ Seis-mic_ Refractions_2015-05-07.ppt.pdf