The waves of practical interest in reflection seismology are usually complicated
because the propagation velocities are generally complex.
In this book, we have chosen to build up the complexity of the waves we
consider, chapter by chapter. The simplest waves to understand are simple
plane waves and spherical waves propagating through a constant-velocity medium.
In seismology however, the earth's velocity is almost never well approximated
by a constant.
A good first approximation is to assume that the earth's
velocity increases with depth.
In this situation, the simple planar and circular wavefronts
are modified by the effects of *v*(*z*).
In this chapter we study the basic equations describing plane-like
and spherical-like waves propagating
in media where the velocity *v*(*z*) is a function only of depth.
This is a reasonable starting point,
even though it neglects the even more complicated distortions that occur
when there are lateral velocity variations.
We will also examine data that shows plane-like waves
and spherical-like waves resulting when waves
from a point source bounce back from a planar reflector.

12/26/2000