Small-magnitude aftershocks are expected by the Arizona Geological Survey following a swarm of mini-quakes in northwestern Arizona that began in late March.
No damage was reported from any of the earthquakes, but there were more than 42 of them starting on March 28, according to the AZGS. The biggest one was a 3.7 magnitude that hit near Littlefield just after 9 p.m. on Sunday.
The swarm began with a 2.1 magnitude "event" about 29 miles southeast of Littlefield, with the most recent one being a tiny 1.3 magnitude quake recorded at about 5 p.m. on Monday.
Sunday's quake was felt by folks in Littlefield, Mesquite Nevada, and along the Nevada-Arizona border in "an area of active crustal extension and seismicity," states the AZGS.
The swarm reflects an "apparent increase" in activity, as opposed to a real increase, the agency says. The Nevada Seismological Laboratory has been trying to find and record small-magnitude earthquakes in the area — and it's been successful.
Arizona's not known for earthquakes like its unstable neighbor, California. But four years ago, a new scientific survey of micro-quakes in Arizona proved the area isn't nearly as geologically quiet as thought previously. Arizona State University researchers, using special equipment on loan from the National Science Foundation's EarthScope program, found that nearly 1,000 small quakes shook Arizona between 2006 and 2009.
Experts say that a "Big One" is possible in Arizona someday.
Northern Arizona has experienced a few historic, fairly large quakes, including one near Williams in 1912 that ripped a 50-mile-long crack in the earth north of the San Francisco Peaks. In 1887, a 7.5-magnitude quake struck Sonora, Mexico. It was the largest earthquake known to have occurred in the region in the recent past and was felt throughout Arizona, says Mike Conway, chief of the AZGS extension service.
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"It did some damage in Tucson — people couldn't stand up as the ground shook," Conway says. "If it had hit today, it would have done quite a bit of damage in the [southeastern] part of the state."
More than 50 people died in Sonora after a church and other buildings collapsed, but there were no known injuries or deaths in Arizona.
Back in November, many Phoenicians heard the boom of a 4.1-magnitude temblor that struck near Black Canyon City. Conway says that quake wasn't part of the recent swarm in northwest Arizona.