Can you visualize movements better now, asks of troy...

Yep. That worked well, especially the bedframe's cracking.

But I do find the lateral movement most interesting of all the movements: one tectonic plate moving north against another moving south.

Subduction makes a lot of sense; and so does its near opposite that causes rifts and even eventual formation of continents that have been pushed apart. But lateral movement--one plate crunching against another moving north and the other plate crunching against the former moving south....well, that just blows my mind.

Magma pushing huge chuncks of land apart through rifts just makes mechanical sense. And Subduction makes a tremendous amount of sense, particularly when an ocean plate moves against a continental plate and is subducted because ocean earth is so much heavier and denser.

But back to lateral movement: To consider two enormous plates comprised of all kinds of soil and bedrock layers moving very, very hard against each other--one moving north and the other south. Why? Why would one tectonic plate move north and the other tectonic plate move south? Some huge force underneath the earth causing one plate to move north and the other south...but what's really going on there? Although in the case of the Loma Prieta quake the Pacific plate did rise upward...

Fortunately, there are hundreds of sites that offer the kind of elementary explanations I'm seeking. But I still haven't found a single site that really explains why tectonic plates should move laterally against each other--you know, the cause and effect kind of thing. I'll keep plowing away on google...

Thanks for the bed cover metaphor, of troy. That's something good to pull into the maelstrom of images I have going on to try to get some working visual image that works.

WW


PS: The thought just occurred: I wonder whether tectonic plates might move laterally when they're composed of equally dense material? For subduction to occur, I think one plate has to be denser than the other and is therefore subducted under the other. Maybe with laterally moving plates both plates are equally dense...and so neither really gives into the other and their push against each other causes opposite lateral movement...? Just a thought. Oh, well. On to the tectonic sites for children...