Geology Reference
In-Depth Information
Fault Linkage and Growth versus Extinction
STAGE 1
STAGE 2
“a” faults
becoming
inactive
Distributed faulting
on inward- and
outward-dipping
faults
a
3
Slip focused on
inward-dipping
fault arrays
a
3
b
2
b
2
c
2
a
2
a
2
c
2
a
1
a
1
b
1
b
1
c
1
c
1
extension
direction
A
B
STAGE 3
Fault slip through time
“a” &”b” faults
in shadow
zone
a
3
Slip migrates
to longest
inner fault
Stage 3
Stage 1
Stage 2
b
2
a
2
5
4
3
2
1
many faults
active
both dip
directions
low slip
rates
faults link
higher slip
rates
“a” faults
slower
c
1
“c” fault
acclerates
inactive
“a” & “b”
faults
a
1
b
1
c
1
C
0
20
30
10
D
Time (My)
Fig. 4.13
Fault linkage, shadow zones, and slip rates during extension.
Synthesis of extensional fault development based on rifting in the Viking Graben, North Sea. A. Distributed faulting
with dips in both directions and slow overall extension. B. Outward-facing faults die and “a” faults slow as “b” and
“c” faults extend, link, and speed up. C. Through-going “c” fault absorbs almost all slip and accelerates; “a” and “b”
faults in shadow zone become largely inactive. D. Changes in slip rates and behavior of interacting faults. Modified
after Cowie
et al.
(2005).
Importantly, compared to the other models, this
model predicts a vertical trajectory in length-
displacement space through time (Fig. 4.11), a
pattern at odds with common assumptions of
how faults accumulate slip.
Another way to visualize linkage among faults
is to imagine a competition among different
fault segments in which the “big guy wins”
(Fig. 4.13). Consider a homogeneous medium
subjected to tensile stresses that cause numer-
ous small defects or extensional faults randomly
distributed across the surface. With continuing
extension, these “defects” lengthen, and as they
grow laterally, some of them happen to encoun-
ter other lengthening faults. These segments
then link up, creating a longer fault that accom-
modates increasingly more displacement. This
linkage also creates a “shadow zone” where pre-
viously formed faults become inactive, because
the larger fault is taking up all the strain in that
sector of the deforming plate. Eventually, larger
fault segments link together to form a through-
going, master fault, and virtually all the other
faults die. As slip gets concentrated on a single
master fault, its slip rate may rapidly accelerate.
Both numerical models and limited field
