A small city in Oklahoma was hit by 20 earthquakes in nine hours overnight, including a pair of particularly strong ones just 30 seconds apart, the United States Geological Survey (USGS) said.

The earthquakes occurred between 10:27 p.m. and 7:40 a.m. and were centered just northwest of Fairview, a city of about 2,600 people that sits about 100 miles northwest of Oklahoma City.

The swarm began with magnitude 4.7 and magnitude 4.8 earthquakes 30 seconds apart. The second quake was the strongest in the state since November 2011, according to the Oklahoma Geological Survey, and only three stronger earthquakes have occurred in Oklahoma since 1882.

The 18 quakes that followed ranged in magnitude from 2.5 to 4.0, USGS data indicates.

The strongest earthquake could be felt more than 100 miles away in other parts of Oklahoma, Kansas and Texas, according to user-submitted reports published on the USGS website. There was no indication that any of the 20 earthquakes caused any significant damage or injuries.

Last April, the Oklahoma Geological Survey issued a statement saying the state’s seismicity rate was 600 times greater than it was before 2008. Wastewater from the oil and gas companies that operate in the state has been linked to the rise, and the Oklahoma Corporation Commission has taken steps to limit the amount of wastewater in an attempt to reduce the overall risk of quakes.

The Oklahoma Corporation Commission on Monday announced additional steps it would take to limit such waste near Edmond, which had felt two sizeable earthquakes in recent days — a magnitude 4.3 earthquake on Dec. 29 and a magnitude 4.2 earthquake on New Year’s Day.

But USGS data indicated three smaller earthquakes occurred near Edmond between 7:20 p.m. Wednesday and 12:42 a.m. Thursday. The tremors ranged in magnitude from 2.5 to 3.2.

Edmond, one of Oklahoma’s largest cities, is located 15 miles northeast of Oklahoma City.

The Oklahoma Geological Survey and USGS have both warned the increase in large earthquakes — those greater than magnitude 3.0 — puts Oklahoma more at risk for even bigger earthquakes.