The larger M4 thrusts are trying to fill in the Oklahoma Seismic Gap. As I have said, there is no great explanation for this, but now I'm suspecting that they simply aren't injecting there. That would be for 2 reasons, one is that the rock is tight all the way down, and the other is that they simply haven't got there yet.
I like to think they inject near cities and towns, so they can go for a beer at lunch. This picture shows that the gap is totally empty. Maybe the earthquakes don't like it because there's nobody to scare! :)
Update: Another M4.1 in Kansas. They're much stupider than OK, no seismometers, and no fault plane solution. :)
Update2: They got a focal plane solution.
Totally normal (tension). This is usually the first failure mode of stressed rock. It results in very little PGV, unlike a thrust.
Update3: It's looks like a record for significant earthquakes. I'll be long in bed before the date closes. I'm really beginning to think that all the mechanisms will converge, and this monster is much bigger than New Madrid. I'll feel the big one here in Toronto!
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