Oklahoma sees more severe earthquakes, fewer overall

(Information from: Tulsa World, http://www.tulsaworld.com)
TULSA, Okla. (AP) – Oklahoma’s 4.0 earthquakes are up significantly this year, but the overall rate of earthquakes continues to decline.
The Tulsa World reports that Oklahoma has had six quakes of at least magnitude 4.0 halfway through this year, which is one more than all of last year. A magnitude 4.6 in April near Perry is the 12th largest in state history.
But there the overall rate has declined, with 96 quakes of magnitude 3.0 or greater through June 30, compared to 144 at this point last year and 302 by the end of 2017.
State seismologist Jake Walter says much of what scientists see is continued earthquakes on unmapped faults that were activated in 2014 by wastewater injection. Walter says scientists are researching specific mechanisms by which the state’s ongoing seismicity is triggered.