Example: Given the above geometry and one spreading velocity VAC what are the other two spreading rates?
= 120 mm/yr,
sum of interior angles = 180˚
Solving for the lengths of the vectors we find VBA = 118.45 mm/yr and VCB = 31.12
mm/yr. One of these flat-earth triple junction closure problems will be on the quiz. The map on the next page shows the other triple junctions. As an exercise, use a bathymetric
map (e.g., Google Earth and this KMZ-file ftp://topex.ucsd.edu/pub/srtm30 plus/SRTM30 PLUS V7.kmz
geometry of another triple junction and use Table 1 (below) to calculate the spreading rate at one of the ridges. The next section develops the mathematics for calculation of plate motions on a spherical earth.