Federal scientists forecast that Oklahoma will continue to have the nation's biggest man-made earthquake problem but it probably won't be as shaky as recent years.
In its annual national earthquake outlook, the U.S. Geological Survey reported Wednesday that a large portion of Oklahoma and parts of central California have the highest risk for a damaging quake this year: between 5 and 12 percent.
Natural elevated quake risks exist through much of California, Seattle and the area where Missouri, Tennessee, Arkansas and Illinois come together, known as New Madrid. Seismologists say Oklahoma's problem is triggered by high volume ground injections of wastewater from oil and gas drilling.
USGS seismic hazard chief Mark Petersen says Oklahoma's recent regulation of wastewater injection is starting to work, so scientists slightly reduced Oklahoma's risk this year.