USGS upgrades latest earthquake to 5.6; strongest on record in Oklahoma

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Lincoln County Emergency Management is reporting significant damage.

The magnitude 5.5 April 9, 1952, earthquake centered near El Reno affected most of Oklahoma and parts of Arkansas, Iowa, Kansas, Missouri, Nebraska, and Texas. Damage from the 10:30 a.m. CST earthquake was not extensive, but many people in the epicentral area were alarmed, some to near panic. Portions of chimneys fell in El Reno and Ponca City (intensity VII). Bricks loosened from a building wall and tile facing of commercial buildings bulged at Oklahoma City. Also, plate glass windows were shattered in the business district of El Reno. The total damage amounted to several thousand dollars. Aftershocks were felt on April 11, 15, and 16, July 16, and August 14; an earthquake that was felt (IV) at Holdenville and Wewoka on October 7 apparently was unrelated to the April 9th event. Homes and buildings shook and some persons were awakened (V) at El Reno from the April 16th shock, which occurred 5 minutes after midnight. Felt reports were also received from Kingfisher, Oklahoma City, Tulsa, and Union City.

That location is about at the northern edge of the Nemaha Ridge. I found a document detailing a safety study done in 2004 for a mine to be located at the north end of Nemaha Ridge, which according to the study is a buried granite mountain range extending roughly from Omaha to Oklahoma City. The mountains were formed about 300 million years ago and have abrupt elevation changes. The complex fault system that bound the ridge is still active today, especially the Humboldt fault zone that forms the eastern boundary of the Nemaha Ridge. In places it breaks through to the surface, and that does not sound like a good characteristic for a fault to have.

SPARKS, Okla. – A record 5.6-magnitude earthquake hit Oklahoma late Saturday night, causing "significant" damage to buildings at nearly the same position that a 4.7-magnitude quake hit less than 24 hours earlier.