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