Geology Reference
In-Depth Information
Displacement With and Without Barriers
nucleation near
restricted tip
unrestricted fault growth
trajectory of
maximum displacement
trajectory of
maximum
displacement
(24%)
(4%)
propa-
gation
propa-
gation
propagation
barrier
nucleation
point
fault length
nucleation
point
A
D
propagation toward
barrier
restricted at one tip
(15%)
(15%)
propagation
stopped by
barrier
propa-
gation
barrier
barrier
B
E
restricted at both tips
propagation past barrier
convergence on
semi-elliptic
a
l form
(13% of all
types)
(28%)
ruptured barrier
barrier
barrier
C
F
Fig. 4.10
Models for fault displacement patterns, Afar Depression.
Patterns of cumulative fault displacement resulting from multiple earthquakes. Darker to lighter shading represents
displacement patterns from early to late in the fault history. The percentages in each box refer to the fraction of
normal faults in Afar showing each class of profile. A. Triangular profiles result from unrestricted fault propagation
with either bow-like or box-like displacement in individual seismic events. Note the nucleation point in the center of
the fault and symmetrical propagation away from the nucleation point. Only 4% of 240 faults fall into this category.
B. Symmetrical propagation becomes restricted at one fault tip by a barrier, causing a steepening of the displacement
gradient. C. Barriers at each end of a symmetrically propagating fault create steep slip gradients on either end of the
fault and continued slip causes the profile to evolve from triangular to semi-elliptical. D. When the nucleation point
occurs near a barrier, propagation is primarily away from the barrier, creating an asymmetric triangular profile.
E. If an asymmetrically propagating fault (as in D) encounters a barrier, it evolves toward a semi-elliptical slip
profile. F. If a barrier is eventually breached at either or both tips of the fault, a tapered tail of slip can develop.
Modified from Manighetti
et al.
(2001).
through time (Manighetti
et al.
, 2001) within
fault systems (Fig. 4.10) suggests that, whereas
a succession of earthquakes could rupture in a
similar, characteristic fashion, overall the
pattern of slip will change both with time and
as a function of interactions with barriers or
other faults.
Fault segment linkage
What happens when individual faults extend
toward each other during the course of multiple
faulting events? Are large faults the result of
linkage between several smaller fault segments,
or do they represent simple lateral propagation
