A swarm of mostly small earthquakes in a remote part of northwestern Arizona has entered its fourth week, gently shaking the sparsely populated area while piquing the curiosity of scientists from afar.
There have been over 40 small quakes near the Arizona-Nevada line since the swarm started March 28. They've ranged from a magnitude 0.4 on April 9 to a Sunday evening quake of magnitude 3.7.
Mohave County Sheriff's Office dispatchers were unaware of any reports of injury or damage, spokeswoman Trish Carter said Tuesday.
The Sunday evening quake was felt in Littlefield, located along Interstate 15 in the Arizona Strip region north of the Grand Canyon, and in Mesquite, Nevada.
"I felt a jolt," said John Lampos, a Mesquite resident and the owner of a storage business in Littlefield. "I thought maybe they were doing night bombing."
The Arizona Geological Survey said the swarm is occurring along the boundary between the Colorado Plateau and a region with active faults, the Basin and Range Province.
Michael Conway, chief of the survey's Geologic Extensive Service, said northwestern Arizona and southeastern Nevada have had swarms before but that the extent isn't clear because there weren't many seismometers in the region.
"With small (earthquakes), below magnitude 2, we would have difficulty picking them up," Conway said from Tucson. "We may be seeing something that isn't so unusual."
However, the Nevada Seismological Laboratory at the University of Nevada, Reno, has expanded its monitoring network in recent years so smaller quakes in the region of the swarm now can be monitored, Conway noted.
"We'll be looking more carefully at that region," he said.
Ken Smith, manager of the Nevada lab's seismic network, said the swarm has been monitored with the help of University of Utah sensors in southwestern Utah. The state systems share data through a national network.
Smith said swarms tend to slowly run themselves out.
The Arizona survey has only eight monitoring stations statewide. The two closest to Littlefield are at the North Rim of the Grand Canyon and at Kingman, each over 110 miles away.
The survey is requesting funding for additional stations, Conway said. "We're not content at all with eight seismometers."