IANAG but IIRC quakes often happen in bunches like this as the earth's crust set...

harshpotatoes · on April 7, 2011

Yeah. I guess. And doing some more looking on the internet and possibly answering my own question, maybe: http://en.wikipedia.org/wiki/Earthquake_swarm

It's hard to find useful information on line about this. But I guess that the lack of information in itself probably means that geologists aren't particularly worried about it.