The link below is for a really interesting book about plate tectonics and continent formation. Dr. Pavel Kalenda and his colleagues evaluated probably all of the current theories for continent formation and tectonic plate movement and explained both processes in detail.

I have read the book several times. But that was a while ago and I can’t remember they evaluated the latest theory that I have seen regarding why earthquakes occur in the New Madrid fault zone and in New England where there are no tectonic plate boundaries.

The most popular theory that I had heard about before last week was that in the New Madrid area, the center of North American plate is slowly moving upwards because the weight of the glaciers on that area has been removed. And the upwards strain causes earthquakes to occur.

The latest theory that I saw just this past week proposes that these earthquakes occur because of plate tectonics. The plates are trying to move relative to one another. And that puts pressure on areas in the center of the plates etc. They respond by having earthquakes.

From what I can remember, Pavel’s main plate tectonic theories involved the top layers of the crust trying to slide across lower “liquid” layers. And at certain locations the plates get temporarily “stuck” because of some obstruction on the bottom of the top layers that keeps them from moving. Earthquakes and plate tectonics can result from that.

Continent formation is associated with yearly sun heat related expansion and contraction of the upper crust. Cracks form in the rock layers related to that expansion and contraction. And debris falls into those cracks from above. As a consequence, continents gradually grow in size relative to the our oceans' size.

His technical exlanation was a little different than that. It involved certain types of sun heat related stress waves if I remember correctly. But in very simple terms that is what I believe it amounts to.

Pavel and another geologist had some arguments about all of this on this bulletin board a while back.

• Pavel Kalenda's Plate Tectonics Book