Seismic security

Oklahoma earthquake reignites concerns that fracking wells may be the cause

A 5.0 magnitude earthquake that rattled north-central Oklahoma Sunday was only the sixth of that strength in state history and has reawakened concerns that oil and gas activity could be causing the tremors.

The temblor, which occurred around 7:44 p.m. Sunday about a mile west of Cushing, Okla., sheared bricks off buildings, caused structural damage to homes and forced local schools to close Monday. Around 40 residents were evacuated from a retirement home and sheltered at a local gymnasium.

It was only the sixth 5.0 magnitude or higher to strike Oklahoma since 1882, said George Choy, a geophysicist with the U.S. Geological Survey in Boulder, Colo. Three of those larger quakes occurred this year. The strongest ever recorded in Oklahoma was a 5.8 magnitude that hit Pawnee in September.