Geoscience Reference
In-Depth Information
Geometry
Velocity triangle
Stability
Possible
Examples
Geometry
Velocity triangle
Stability
Possible
Examples
RRR
Stable if the
angles between
and ,
respectively,
are equal, or if
, form a
straight line
TTR(b)
ab
All orientations
stable
East Pacific
Rise and
Galapagos
Rift Zone,
Indian Ocean
Triple Junction
C
A
B
ac
A
B
A
B
bc
ab
ac bc,
bc
C
ac
C
B
A
ab
ac bc
C
TTT(a)
C
ac
TTF(a)
ab
ab
C
Stable if ,
form a straight
line, or if is
parallel to the
slip vector CA
ab ac
Central Japan
Stable if ,
form a straight
line, or if C lies
on
ac bc
Intersection of
the Peru--Chile
trench and the
Chile Rise
bc
bc
A
B
A
B
B
bc
B
C
C
ab
ac
A
A
TTT(b)
C
Stable if the
complicated
general condi-
tion for , b
and to meeting
at a point is
satisfied
ac
ab
C
TTF(b)
ab
Stable if ,
form a straight
line, or if
goes through B
bc ab
B
bc
A
B
A
B
ab
c
bc
ac
B
ac
C
ac
C
A
A
C
TTF(c)
FFF
ab
ab
Stable if
form a straight
line, or if
do so
ab, ac
B
B
A
B
ac
A
B
Unstable
bc
ac
ab, bc
C bc
A
C
C
A
FFR
Stable if C lies
on or if
form a
straight line
Owen fracture
zone and the
Carlsberg
Ridge,
Chile Rise
and the East
Pacific Rise
RRT
ab
B
bc
ab,
ac, bc
C
ac
A
ab must go
through
centroid of ABC
A
B
B
A
bc
ac
C
ab
B
A
C
C
FFT
RRF
A
ab
ac
ac
Unstable,
evolves to FFR;
but stable if
and are
perpendicular
ab
Stable if
form a straight
line, or if
do so
ab, bc
San Andreas
Fault and
Mendocino
fracture zone
(Mendocino
triple junction)
B
A
B
A
B
B
A
bc
ac, bc
C
C
bc
C
ab
ac
C
RTF(a)
TTR(a)
ac
Stable if goes
through C or if
form a
straight line
ab
Mouth of the
Gulf of
California
(Rivera triple
junction)
Stable if
goes through C,
or if form
a straight line
ab
C
ac
ab
C
A
B
A
B
bc
ac, bc
ac, bc
B
C
bc
C
A
B
A
ab
RTF(b)
TTR(b)
C
C
Stable if com-
plicated general
conditions are
satisfied
AB
bc
ac
Stable if
cross on
ac, ab
bc
A
B
bc
B
C
A
ab
C
A
B
ab
ac
Figure 2.16.
The geometry and stability of all possible triple junctions. In the
categories represented by RRR, RTT, RTF and so on, R denotes ridge, T trench and F
transform fault. The dashed lines ab, bc and ac in the velocity triangles represent
velocities that leave the geometry of the boundary between plates A and B, B and C
and A and C, respectively, unchanged. A triple junction is stable if ab, bc and ac meet
at a point. Only an RRR triple junction (with ridges spreading symmetrically and
perpendicular to their strikes) is always stable. (After McKenzie and Morgan
(1969).)
