People where I live still talk about the New Madrid earthquakes that occurred in southern Missouri in 1811 and 1812. I've heard that church bells rang hundreds of miles away in New England, disturbed by the seismic waves, and supposedly the surface of the earth subsided as a result of the quakes to such a degree that it created a new lake (Reelfoot Lake in Tennessee). The aftershocks go on to this day.

I spent part of my childhood in southern California and grew up with the instructions about standing in a door jamb during a quake and all that, so I was used to the idea of California as earthquake-prone, and I understand the reasons for California quakes. It was something of a surprise to me when I learned in my teens about this massive quake in the middle of the continent, far away from any major active tectonic plate boundary, and I gather that it's been something of a mystery what was behind the seismic activity. It turns out that maybe there's a connection between the west coast and the New Madrid area.

A new paper in Geophysical Review Letters suggests that events on the west coast millions of years ago might have led to the New Madrid quakes.

The Farallon plate was a tectonic plate that made up some of the ocean floor between the Pacific plate and the continental plates of North America.

Around 70 million years ago, during the Cretaceous period, it met the continental plate and was forced underneath it, or subducted. The Farallon plate went under at a shallow angle, and hence the subduction process was long and complicated. The plate scraped along the underside of the continent for awhile, and the resulting volcanoes formed the Sierra Nevada in California. Due to motions in the mantle, underneath the crust, the continental plate moved westward over the subducted plate; the progress of the Farallon plate under the continent was instrumental in forming the Rocky Mountains. And all these millions of years later, the plate is evidently still descending, and as it moves it affects the flow of molten rock in the mantle beneath parts of the eastern US.

The new paper describes how the resulting stresses in the crust could have triggered the New Madrid earthquake, and perhaps could contribute to further seismic activity in the area in the future. This is useful information for predicting what will happen in the area in the future, but it also illustrates a very interesting connection between something so long ago and far away, and something much closer to home.