Recipe for Computing Velocity Magnitude
In summary, to calculate the magnitude of the velocity:
i)
Transform lat, lon into x = (x, y, z) unit vector using equation 5.
ii)
Transform pole lat and lon into x_{p }= (x_{p, yp, zp) unit vector }
iii)
cosΔ = x • x_{p }
iv)
v = ω a sinΔ
p x = 0.0148
x = 0.375
p y = 0.606
y = 0.862
p z = 0.795
z = 0.342
cosΔ = x•x_{p = (0.0056 + .522  .272) = .244 }
Δ = 75.8˚
v = ω a sinΔ = 142.9 mm/yr
Example: Given the rotation pole between the Pacific and Nazca plates, calculate the spreading rate at –20˚ 113.5˚W. ***One of these calculations will be on the quiz***
52.7
88.6 1.326 x 10^{6 }deg/yr
52.7
271.4 2.314 x 10^{8 }rad/yr
POLE
POINT
20.0˚S 113.5˚W

20.0 246.5
9