A magnitude 5.2 temblor that occurred on February 10, 2006, about 150 miles (240 kilometers) south of New Orleans may have involved the same fault zone, he adds.
The source of stress is far out in the Atlantic Ocean, where plate tectonics are causing the seabed to spread. This drives the North American plate westward, compressing it.
"All of eastern North America is in similar compression, presumably for the same reason," Cox said by email.
A few weeks ago, Cox published a study of the tectonics of southern North America in the GSA Bulletin, a journal of the Geological Society of America.
"This thrusting event is consistent with prehistoric fault movements we found in the onshore Gulf Coast region," he said by email.
"Until recently it was presumed that the eastern North American plate had a transition from compression in the interior to extension—or stretching—in the Gulf, but we've changed the stress maps of late, and this earthquake fits right in."
Sunday's quake was the second-largest temblor recorded in the past week. The largest, at magnitude 6.3, occurred on Saturday in the earthquake-prone country of Indonesia.
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