FILE - In this Monday, Sept. 12, 2016 file photo, Jeremy Boak, director of the Oklahoma Geological Survey, answers a question during a news conference in Oklahoma City. Boak says the number of quakes larger than 4.0 magnitude has dropped dramatically so far this year, but it's still not clear what caused several large quakes last year that were above 5.0 magnitude. (AP Photo/Sue Ogrocki, File)
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