LITTLE ROCK (AP) — A previously unknown fault in eastern Arkansas could trigger a magnitude 7 earthquake in the cotton fields of the upper South with an epicenter near a natural gas pipeline, a scientist said Wednesday.

Haydar Al-Shukri, the director of the Arkansas Earthquake Center at the University of Arkansas at Little Rock, said the fault, west of Marianna, is separate from the New Madrid fault responsible for a series of quakes in 1811-12 that caused the Mississippi River to flow backward.

Acres of cotton cover the fault and stretches of fine sand mixed with ferti...