Colorado, Virginia, California: three earthquakes across the United States in three days. Aside from the apocalyptic questions some are raising, was this more than an earth-trembling coincidence? Or was there some scientific connection between these three events?

First there was the magnitude 5.3 earthquake near Trinidad, Colo., the largest earthquake in the state since 1973. Then a magnitude 5.8 quake centered in Mineral, Va., jarred a region from Charleston, S.C. to Boston. Finally, there was a relatively mild 3.6 rattler in the San Francisco area Tuesday night.

What