But the weekend earthquakes were among the strongest yet in a state that has seen a dramatic, unexplained increase in seismic activity.
Oklahoma typically had about 50 earthquakes a year until 2009. Then the number spiked, and 1,047 quakes shook the state last year, prompting researchers to install seismographs in the area. Still, most of the earthquakes have been small.
http://abcnews.go.com/US/wireStory/o...orted-14891887
Was wondering how commen they normally are there(and any fault lines nearby etc)