Thanks for all that.

Before you replied I eventually realized that even a small patch moving on the surface of a sphere is rotating around the sphere on some axis, thus two poles of rotation.

What I'm really having a hard time with is visualizing that the plates, even the harder oceanic crust, is so darned rigid.

Sure, if I take a piece of basalt and squeeze it in a vice, it's not going do do much if anything. But we're talking about strain distributed across thousands of kilometers of crust, and time spans of millions of years.

Surely even basalt is compressible a little?

Further, the crust is not one solid massive block of material, is it? Wouldn't there be voids and fractures that could accommodate compressive or elastic forces? Although, I suppose they may not necessarily store those forces, but simply deform.

Brian