Geoscience Reference
In-Depth Information
Figure 9.7.
(a) The record section of an expanding-spread (wide-angle) profile shot
over 118-Ma-old oceanic crust southwest of Bermuda on the North American Plate.
The records have been band-pass filtered at 6-30 Hz and plotted with a gain
(amplification) that increases linearly with distance and as the square of the travel
time. The P-wave arrival, P
3
,isalower-crustal refraction. The S
3
arrival is the
lower-crustal S-wave. The strong secondary P-wave arrival seen between 20 and
35 km is a refraction from the upper mantle. Arrow; near-normal-incidence reflection
from the Moho. The large-amplitude hyperbola, which is the first arrival at
