There are 181 fracking injection wells in the Oklahoma county where most of the weekend earthquakes happened,
Oklahoma typically had about 50 earthquakes a year until 2009. Then the number spiked, and 1,047 quakes shook the state in 2010.
Scientists say they have no explanation for the quakes.
They happened along an ancient fault, although it’s not clear yet whether shifting along the fault is what caused them,
Arkansas also has seen a big increase in earthquake activity, which residents have blamed on injection wells.
Natural gas companies engaged in hydraulic fracturing, or fracking, use fluid to break apart shale and rock to release natural gas.
Injection wells then dispose of the fluid by injecting it back into the ground.
There are 181 injection wells in the Oklahoma county where most of the weekend earthquakes happened,
Lately, there also was highly unusual earthquake in Colorado and East coast.
Earthqukes can ge triggered artificially, with Haarp technology.