Page 188 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

to strong
of
of
of
Seismic
chaotic;
migrated
Fig.
deep-sea
and
Fig.
faults
seismic
also
beneath
the
sedi-
mid-ocean
mountain
crust
basement, hemipelagic sedi-
of km
1982;
contrasts within
newly-formed
between
mid-
wedges.
(accretionary
faults
171
toe
areas
portions
beneath
1991;
side,
Sediments
hemipelagic
are
oceanic
al.,
a
older normal
thrust
the
tens
at
6.34c).
Settings
poor
accretionary
are
deformed.
toe
s
sediments
Boundaries
et
lead
to
(right
2
Westbrook,
developed
at
some
ridge:
parallel
commonly
about
rearward
reflections
(Moore
addition
time)
the
and
were
to
of
wedge.
can
structural
(Fig.
across
Tectonic
impedance
wedges
least
leads
top
Wedge
strata
from
mid-ocean
by
they
travel
reflections, also
deformed)
the
Moho
accumulates
two
structurally
the
Complex
covered
accretionary
In
from
2,
the
at
impedance.
and
(Figs-6.33a, 6.34a).
profiles
wedge,
deformation
differs from
that
of trench
pronounced:than
profiles
layer
6.4a),
that
beneath
of
(two-way
one
accretionary
Accretionary
Crust
of the
in
Bangs
seismic profiles
Expression
(Fig. 6.32b). Acoustic
toe, so
oceanic
a
structure
zone,
often
generally
shows
accretionary
at
oceanic
reflection
Ridge
Fig.
of Oceanic
position
Reflection
are
formed
that
Offsets
1988;
traced
show flat-lying
s
acoustic
the
the
1982;
but
of normal faults
subduction
2
the
intense
6.32a
region
and
Barbados
of
approximately
at
Seismic
beneath
complex
al.,
hummocky,
undeformed
are
Deformed
offset
crust
be
al.,
side, Fig. 6.33b).
sediments
were
the
On
regions
less
dewater
et
at unmigrated
and
the
Defining Top
Fig.
often
in
et
6.28c).
more
low
1983; Westbrook
of oceanic basement, indicating
become
oceanic
they
faults
Reflections
within
of km
(Nasu
contrast
basement
the
a
The
the
Sediments
of
can
regions
basin
toe
however,
materials
of
of
set
than
trench-fill
image
top
(sometimes
flexural
like
(Fig.
(arc).
are
tens
6.28b),
side, Fig. 6.4b).
the
Trough
after
distance
contrasts
expression
This younger
Expression
forearc
less
continuous
on
instances,
events
(right
oceanic
Events
look
wedge
in
for
2
to
volcanic
Moho
soon
form
(Figs. 6.27, 6.28a);
arcward,
Basin
6.27,
to
imaged
difficult
layer
Nankai
of the
axis,
laterally
Smith,
to
Atsome
the
wedges
density
crust, Moho
leading
strata
trench/accretionary
produced
is useful
Hyperbolic
the
commonly
characteristic
Flat-lying
(Figs.
some
trench
is
Forearc
Chaotic
one
some
oceanic
(Fig. 6.33).
less
and
(left
ranges
cut
well
the
therefore
Farther
basin
traced
accretionary
and
and
ridge
and
wedge,
faults
Westbrook
In
and
resolution
ments, and
sections, it
Basement
often
the
were
velocity
oceanic
wedges.
forearc
8.
the two
steeper
wedge)
6.
5.
7.
top
of
ranges
be
6.34b)
ocean
6.4b).
ments
faults
from
ridge
that
is
The
are
top
can
the
the
it
reflections. Range Mountain Collisional Reflections structural* because variety widé a ranges span mountain collisional from nonethe- signatures, reflection Key 6.36). 6.35, (Figs. collision during change styles (“fore- plate downgoing the of craton the from traverse a of characteristic are less, (“hin

Profiles sediments layer 2. of a
Reflection Wedge Ridge deformed). basin. and oceanic ecrotioinaiy wedge, the outer forearc region
Seismic Formed or Enhanced at Flexural Bulge of
Of Region Faults: Formed at Mid-Ocean and deep-ocean basement lop figure). observed in
Interpretation Forearc Accretionary Normal / (undeformed from deformed (previous
Tectonic Outer | layer. from offsetting (unmigrated) reflections. of highly and reflection sequences (b) commonly
And of ; Sediments Sediments water sediments faults sediments
Structural Section Trench-fill Hemipelagic Signature sediments normal above). events Moho expression basin (a)
Chapter6 Cross Flexural Bulge et 4 Reflection Transparent Trench-fill Hemipelagic Flexural "a" (in Hyperbolic Flat-lying Chaotic Forearc Cross section (Fig. 6.32b).
170 Crustal 1. 2. 3. 4, 5. 6. 7. 8. 6.33 FIGURE subduction zone
a) b)