Earthquakes rattled residents in Oklahoma on Saturday, the latest in a series that have put the state on track for record quake activity this year, which some seismologists say may be tied to oil and gas exploration. One earthquake recorded at 3.8 magnitude by the U.S. Geological Survey rocked houses in several communities around central Oklahoma at 7:42 a.m. local time. Another about two hours earlier in the same part of the state, north of Oklahoma City, was recorded at 2.9 magnitude, USGS said. Those two were preceded by two more, at 2.6 magnitude, and 2.5 magnitude, that also rolled the landscape in central Oklahoma early Saturday morning. A 3.0 magnitude tremor struck late Friday night in that area as well, following a 3.4 magnitude hit Friday afternoon. More