Geology Reference
In-Depth Information
1.7.3
Seismic Reflection Profiles
Many interpretations of subsurface structure are based on seismic reflection profiles.
Sound energy generated at or near the earth's surface is reflected by various layer
boundaries in the subsurface. The time at which the reflection returns to a recorder at
the surface is directly related to the depth of the reflecting horizon and the velocity of
sound between the surface and the reflector. Seismic data are commonly displayed as
maps or cross sections in which the vertical scale is the two-way travel time (Fig. 1.46).
The geometry of a structure that is even moderately complex displayed in travel
time is likely to be significantly different from the true geometry of the reflecting
boundaries because of the distortions introduced by steep dips and laterally and ver-
tically varying velocities (Fig. 1.47). Reflections from steeply dipping units may return
Fig. 1.46.
Time-migrated seismic profile from southern Appalachian fold-thrust belt (Maher 2002), dis-
played with approximately no vertical exaggeration. The vertical scale is two-way travel time in sec-
onds.
a
Uninterpreted.
b
Interpreted
