Earthquakes and volcanic eruptions

Why aren’t there more volcanic eruptions resulting from earthquakes? I’m thinking of the tectonic plates grinding against (or over or under) each other, sometimes causing rifts. It seems like this would be a great opportunity for magma to escape to the surface. Is the magma too far down, and earthquakes more superficial than I’m assuming? Or not enough pressure, or not enough of a rift? I realize there are many variables, but it seems that magma should escape more often than it does.

IANA vulcanologist, but volcanoes often occur somewhat away from where the two plates meet (q.v. the Rockies). What happens is that if one plate is subducted - forced down into the mantle - and melts, it’s this melted plate that forms the magma which, being lighter than the mantle, rises to form the volcano. And it has plenty of CO2 and H2O with it to move things along. AIUI it’s ocean floor plates that get subducted; continental plates meeting form mountains like the Himalayas.

Then you’ve got Iceland where the two plates are moving apart and you have plenty of volcanoes.

A third type is a travelling hotspot, characterised by a chain of islands, like Hawaii. I’m not sure whether it’s the hotspot itself that moves or the plate that moves over the hotspot.

You got all of it correct except the Rockies. They sit in the middle of the North American tectonic plate and, generally speaking, were caused by uplift. Ocean plates subduct under continental plates because the latter is lighter. Two famous hot spots are the Hawaiian Islands hot spot and the Yellowstone hot spot. Both are caused by mantle plumes breaking through a plate as the plate moves over it.

Compare this earthquake map with the plate tectonics map. Notice anything?

What explains the terrible earthquakes in about 1812 in the area of the bootheel of Missouri? Is that explained by plate tectonics?

That earthquake map is amazing!

The New Madrid Seismic Zone, with probably more than you wanted to know about it at the link.

Thank you very much, sir. Much appreciated.

It’s always reassuring to know that if I live long enough to see my great-grandchildren married, I’ll probably experience an 8.0 earthquake!

According to this article, all of the little bitty earthquakes that I grew up with in childhood are still considered aftershocks of the big ones from 1811 and 1812.

In examining one map of what is considered the hot zone for the New Madrid Fault, I see that I grew up in the red dotted area and Tina Turner grew up in the solidly red area. Ah! That explains the difference!

It is good to see that Richmond and Boston had church bells though.

Interesting stuff.