# SO461, Quiz 2, Fall 2014

The diagram above shows the velocities of three plates in the MORVEL plate model.  The map to the left shows the orientations of the three boundaries and their triple junction.

If  the P1-P2 boundary is a trench,  plate P1 subducts.

If  the P3-P2 boundary is a trench,  plate P2 subducts.

If  the P3-P1 boundary is a trench,  plate P3 subducts.

Determine the type of boundary for each of the three plate boundaries, and draw relative motion arrows on each.

Is the triple junction stable?

How will the triple junction migrate with respect to the three plates?

The analysis of the triple junction.  The green lines connect the points with the three plate velocities, and give the relative motions for each pair.  The red lines show the possible locations of the triple junction considering each pair of plates.

• P1-P3 is a trench, and its line goes through the velocity point for the upper plate (P1) with the orientation of the trench on the map.

• P1-P2 is a ridge, and its line is the perpendicular bisector for the line connecting the velocity points for the P1 and P2

• P2-P3 is a transform, and its line goes through the velocity points for the P2 and P3

The three red lines intersect at a point, so the triple junction is stable.  It will also migrate with respect to each plate, moving NW away from P1, and NE from both P2 and P3.

The actual triple junction that inspired the problem.  The orientations of the boundaries were slightly modified.