Download From Seth Stein`s Euler pole exercise

Euler pole description of relative plate motion
PACIFIC
NORTH AMERICA
From Seth Stein’s Euler pole exercise
Euler pole description of relative plate motion
PACIFIC
NORTH AMERICA
Trace (a portion of) the plate
boundary on tracing paper
From Seth Stein’s Euler pole exercise
Euler pole description of relative plate motion
Spin tracing paper clockwise
around the thumbtack,
representing Pacific Plate motion
relative to North America
PACIFIC
NORTH AMERICA
From Seth Stein’s Euler pole exercise
Euler pole description of relative plate motion
The (small) rotation
represents millions of
years of tectonic motion.
PACIFIC
NORTH AMERICA
From Seth Stein’s Euler pole exercise
Euler pole description of relative plate motion
Ω
•
Suppose a divergent plate boundary lies along
a line of longitude (a great circle)
•
Euler pole (E) = North pole
•
Relative plate motion is along lines of latitude
(a small circle)
•
•
E
δ
v
P
The rate of rotation about the Euler pole gives
rise to variable linear velocities, calculated at
points P.
vmax
The linear velocities are maximized along the
equator (90º away from E) and smoothly
decrease toward the north and south poles.
P
v
Euler pole (E)
Calculation point (P)
Active spreading boundary
Crust created since spreading began
http://commons.wikimedia.org/wiki/File:Globe_Atlantic.svg
Calculating linear velocity from rotation rate
Ω
Ω
δ
E
Horizontal view
(into equator)
E
r = R sin δ
P
δ
R
δ
v
P
vmax
P
v
v = linear velocity (mm/yr)
Ω = Euler rotation rate (º/yr)
R = Earth radius (mm)
δ = angular distance between E and P (º)
E = Euler pole, P = calculation point
P
r = R sin δ
Ω
v = Ωr = Ω R sin δ
Vertical view
(along pole)
Note that the linear velocity is constant along
each small circle (in this case, latitude lines)
Visualizing RPM as small circles around the Euler pole
In the Gulf of California,
greater distance from
Euler pole = faster relative
plate motion
Relative motion means
that one plate moves with
respect to the other
Baja moves NW relative to
North America; North
America moves SE
relative to Baja.
Figure from Bennett et al., AGU talk, 2013
The relative nature of relative plate motion
Baja Microplate
moves NW relative
to North America
Approximate outline of
Baja Microplate
The relative nature of relative plate motion
North America
moves SE relative to
Baja Microplate
Approximate outline of
Baja Microplate
Relationship between RPM and fault slip rates
B
Fault segment: strike 352º
Fault-perpendicular slip
(opening/closing)
A
C
Fault-parallel slip
(strike-slip)
Plate motion:
44 mm/yr @ 313º
A point on the Baja Microplate immediately adjacent to the fault segment (plate
boundary) moves relative to North America as described by the RPM vector
Measuring plate motion obliquity
1
2
3
Measuring plate motion obliquity
1
α
2
3
Relating other faults to oblique rifting
Deformation along riftparallel strike-slip faults
Deformation along riftparallel strike-slip faults
Deformation along
normal faults
perpendicular to RPM
Deformation along
normal faults
perpendicular to RPM
Modified from Dorsey and
Umhoefer, 2012
Structural geology of the Gulf of California
Low-angle
detachment faults
Off-axis normaldextral faults; no
detachment faults
Modified from Dorsey and
Umhoefer, 2012