How Many Plates?
By Don L. Anderson
Purpose of paper
Reviews the history of plate tectonics, and why it is an inexact science. Discusses the question of the optimal shape and size of a tectonic plate and the possible total number of plates, Anderson calls the principle “Platonics.” Shows how using models on a smaller scale, such as foams, help us to determine the larger design of Earths plates.
Data used/observations made
A table of plate parameters shows the relationship between the “7 major plates that account for 94% of the surface area of the Earth,” with some of the smaller plates that are recognized. This table shows: surface area, growth rate, notes, and plate type for each plate.
Figure 1 depicts a graph relating packing density to the number of plates on a sphere.
Figure 2 shows 6 of the 10 possible configurations of great-circle arcs on sphere.
Figure 3 shows a flatten globe where each is an equal area projection.
Interpretations/discussion of data
The plate parameters table shows that although most of the world’s plates behave in a similar manor, they are not similar in dimension or pattern.
Figure 1 shows that the highest packing density, i.e. the smallest amount of void space, occurs when the number of plates is 6 or 12. Using this information, along with volcanic and earthquake trends, leads us believe that there are between 8 & 20 plates, with 12 being the most commonly quoted number.
Figure 2 visualizes the minimal service theory and allows us to see examples of the triple junctions meeting at 120 degrees. 5 of the 6 represent possible optimal shapes of plates and plate boundaries.
Figure 3 shows how the plates fit together and where possible deformation zones occur. Shows that plates typically have five neighboring plates, although they are far from being a typical pentagon shape. Shows the optical packing theory in a more real-world form.
The “ideal world” and the real world have many...