For those of you wanting to know what exactly I was up to last week, or those of you who just can’t get enough shiny technical details. This is a gravity anomaly map of the area I wrote my paper on Monday night, in the southeastern corner of Missouri; the bright yellow stripe down the middle marks a zone where, 600 million years ago, the continent started to split apart. It stopped before getting anywhere interesting, of course, but not before upwelling hot mantle rock had left a layer of dense goop on the bottom of the crust. Now there are earthquakes because of it.
To make your own gravity maps, use this. You’ll need to know some latitudes and longitudes, some of which you can find here or here. I recommend a look at the Hawaiian islands (18-24 N, 165-153W) or the Aleutian trench (50-55 N, 170E-170W).
[a tip o’ the hat to leuschke]