Euler pole description of relative plate motion
NORTH AMERICAPACIFIC
Euler pole description of relative plate motion
NORTH AMERICAPACIFIC
Trace (a portion of) the plate boundary on tracing paper
Trace (a portion of) the plate boundary on tracing paper
Euler pole description of relative plate motion
NORTH AMERICAPACIFIC
Spin tracing paper clockwisearound the thumbtack,
representing Pacific Plate motion relative to North America
Spin tracing paper clockwisearound the thumbtack,
representing Pacific Plate motion relative to North America
Euler pole description of relative plate motion
NORTH AMERICAPACIFIC
The (small) rotation represents millions of
years of tectonic motion.
The (small) rotation represents millions of
years of tectonic motion.
vv
vv
vvmaxmax
δδ
ΩΩ
EE
PP
PP
Euler pole description of relative plate motion
• 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)
• The rate of rotation about the Euler pole gives rise to variable linear velocities, calculated at points P.
• The linear velocities are maximized along the equator (90º away from E) and smoothly decrease toward the north and south poles.
Euler pole (E)
Calculation point (P)
Active spreading boundary
Crust created since spreading began
r r = R sin = R sin δδ
RR
δδ
δδ
ΩΩ
EE
PP
vv
vv
vvmaxmax
δδ
ΩΩ
EE
PP
PPPP
r r = R sin = R sin δδ
ΩΩ
vv = = Ωr Ωr = = ΩΩ R sin R sin δδvv = linear velocity (mm/yr) = linear velocity (mm/yr)ΩΩ = Euler rotation rate (º/yr) = Euler rotation rate (º/yr)R = Earth radius (mm)R = Earth radius (mm)δδ = angular distance between = angular distance between E E and and PP (º) (º)EE = Euler pole, = Euler pole, PP = calculation point = calculation point
Note that the linear velocity is constant along each small circle (in this case, latitude lines)
Calculating linear velocity from rotation rate
Horizontal view(into equator)
Vertical view(along pole)
Visualizing RPM as small circles around the Euler poleVisualizing RPM as small circles around the Euler poleVisualizing RPM as small circles around the Euler poleVisualizing 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.
The relative nature of relative plate motion
Baja Microplate moves NW relative to North America
Approximate outline of Baja Microplate
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
Approximate outline of Baja Microplate
Relationship between RPM and fault slip rates
Plate motion: 44 mm/yr @ 313º
Fault segment: strike 352º
A
B
CFault-parallel slip
(strike-slip)
Fault-perpendicular slip(opening/closing)
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
Average strike of plate boundary
1
2
3
Measuring plate motion obliquity
Average strike of plate boundary
Local direction of RPM
(α
Relating other faults to oblique rifting
Deformation along rift-parallel strike-slip faults
Deformation along rift-parallel strike-slip faults
Deformation along rift-parallel strike-slip faults
Deformation along rift-parallel strike-slip faults
Deformation along normal faults
perpendicular to RPM
Deformation along normal faults
perpendicular to RPM
Deformation along normal faults
perpendicular to RPM
Deformation along normal faults
perpendicular to RPM
Dorsey and Umhoefer, 2012
Structural geology of the Gulf of California
Low-angle detachment faults
Off-axis normal-dextral faults; no
detachment faults
Dorsey and Umhoefer, 2012
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