Geoscience Reference
In-Depth Information
Figure 10.46.
A cross section of the passive continental margin off the east coast
(New Jersey) of the U.S.A. The numbers are the seismic P-wave velocities in km s
−1
as determined from expanding-spread (wide-angle) profiles. Vertical solid lines
labelled Cost give the locations of two deep commercial wells. The deep crustal
layer having P-wave velocity 7.1-7.5 km s
−1
is believed to be igneous material
intruded at the time of rifting; thus, it is very similar to the oceanic layer 3 into which
it merges. (From LASE Study Group (1986).)
Figure 10.47.
(a) Subsidence of the North Sea basin when filled with water only
(corrections have been made for sediment compaction, loading and palaeowater
depth) for five wells that straddle the central graben of the basin. Bars denote range
of basement level; dashed line, calculated fault-controlled subsidence for a model
with steady extension occurring over 60 Ma; solid line, calculated subsequent
thermal subsidence. The model had an initial crustal thickness of 31 km for wells 1, 4
and 5, 25 km for well 2 and 28 km for well 3. (b) Crustal thickness beneath the North
Sea as determined by seismic-refraction experiments. (From Wood and Barton
(1983).)
