A series of small earthquakes swarmed the state’s northwest corner after an initial magnitude 2.3 earthquake on the Arizona strip March 29, officials said Tuesday.

The earthquake that struck near Littlefield, Ariz., a community about 20 miles southwest of St. George, Utah, was the first of 18 small-magnitude tremors that lasted through Sunday, according to the Arizona Geological Survey.

The largest event was a 2.6 magnitude quake at about 8:36 a.m. Sunday. The Arizona Geological Survey has not reported any injuries or damage from the series of tremors.

While the amount of quakes to hit the area may seem unusual, Geological Survey researcher Michael Conway said the state has seen swarms before.

Conway said the area is “tectonically active,” but this was the first time a swarm has been recorded in the northwest corner of the state, bordering Utah and Nevada.

“Active faults in the vicinity of the earthquake swarm include the Mesquite/Overton Arm,” according to an Arizona Geological Survey statement. The area has extensive earthquake history.

The tremors were large enough to register with the seismometers installed in the area but small enough to go unnoticed, Conway said.

He pointed out that the Geological Survey has a duty to record, catalog and remind people that Arizona experiences at least 100 small quakes each year.

According to Conway, there hasn’t been significant technological advances that can predict naturally occurring quakes, but researchers have been able to predict induced tremors in Oklahoma and Texas likely due to fracking.

There have been moderate-sized earthquakes closer to Phoenix, including the Nov. 2, 2015, quake in Black Canyon City, which had a 4.1 magnitude.

Conway advised that if an earthquake happens, “you drop down, get under a desk and hold on.”