OKLAHOMA CITY (AP) -- In Oklahoma, now the country's earthquake capital, people are talking nervously about the big one as man-made quakes get stronger, more frequent and closer to major population centers. Next door in Kansas, they're feeling on firmer ground though no one is ready yet to declare victory.
A year ago, the states had a common problem - earthquakes caused by the disposal of wastewater from oil and gas exploration. They chose different solutions. Kansas, following early scientific studies, decided to restrict how much and how fast the wastewater could be pumped back underground. Oklahoma instead initially concentrated on the depth of the wastewater injections.
Developments since then haven't been reassuring in Oklahoma, where a quake knocked out power in parts of an Oklahoma City suburb several weeks ago and where fears are growing that the worst is yet to come. On Friday, about 200 unhappy residents packed a forum at the state capitol convened by critics of the state's response. A governor's task force is studying the problem but officials have so far avoided taking tougher measures.
The quakes, which have been mostly small to medium sized, have caused limited damage, and no one foresees anything like the massive damage and deaths in the famous quakes in California, seismologists say.
Still, 'It's a trend that's unsettling,' said Cornell University geophysicist Katie Keranen, referring to the increasing number of quakes. Frequent small quakes can be a harbinger of bigger ones. 'You have the ingredients you need to have a larger earthquake.'
In Oklahoma, earthquakes of magnitude 2.7 and stronger increased by about 10 percent between the last half of 2014 and the last half of 2015, according to a data analysis by The Associated Press. Experts say 2.7 is a threshold at which monitors are reliable. In Kansas, earthquakes of that magnitude went down by 60 percent in the same period.
According to earthquake experts, the pattern fits recent peer-reviewed studies that suggest injecting high volumes of wastewater could aggravate natural faults. In Oklahoma's six most earthquake-prone counties, the volume of wastewater disposal increased more than threefold from 2012 to 2014.
The past few weeks have been especially nerve-wracking.
Eighty-eight quakes of 2.7 or stronger occurred this January as of Monday at noon central time, more than in all of 2012. The recent quakes have generally been more powerful, too, with eight of magnitude 4 or higher.