For the second day, a flurry of tiny earthquakes rattled northern Texas, prompting calls to police, public service announcements of safety tips and tongue-in-cheek photos of fallen water bottles.
The quakes, which would hardly raise an eyebrow in California, ranged in magnitude from 1.6 to 3.6, according to the U.S. Geological Survey.
The cluster of quakes was centered in the Dallas suburb of Irving. An additional 3.5 quake occurred in Snyder, about 250 miles west of Dallas.
The two largest — the 3.5 and a 3.6 — hit Tuesday afternoon, surprising residents not used to earthquakes. They inundated 911 operators with 97 calls in the 14 minutes after one quake.
Officials had to tell the public not to call unless there was an emergency or someone was hurt, said James McLellan, spokesman for the Irving Police Department. No injuries or damage was reported, other than some minor wall cracks.
For Ben Guthrie, a 37-year-old software programmer in Dallas, Tuesday was only his second experience with earthquakes. He first felt a quake in 2012 in Tulsa, Okla., but that one was much "fainter," and he didn't really realize what was going on, he said.
Guthrie knew exactly what was going on Tuesday afternoon when his concert posters started wiggling and rattling in their frames on the walls of his home.
"It was like a very large airplane flew overhead and rattled the house," he said. "But also the floor moved."
He said he was scared during the first quake, but by the fourth one, it "stopped being scary." His only concern now is whether this will become a routine occurrence.
"This is very much a new thing," he said. "There are so many new questions that we have now."
Examples of earthquakes in unexpected areas like Texas may seem to be a growing trend, but they could have been happening for years, undetected until now with the use of better technology. Combined with the social media amplification of reports of even small quakes, it may not be an indication of anything unusual, authorities say.
In recent years, however, neighboring Oklahoma has experienced a number of earthquakes, including a magnitude 5.7 temblor that struck 45 miles east of Oklahoma City in 2011. Scientists say the quakes are probably tied to increased use of underground injection wells — involved in hydraulic fracturing, also known as fracking — in the oil and gas industry.
In Dallas, it's too soon for scientists to pinpoint a cause of the quake swarm, said Rob Williams, a geophysicist with the USGS in Golden, Colo. But he said that "human contribution" would not be ruled out. A report on a cluster of earthquakes about five years ago near Dallas-Fort Worth International Airport suggested waste-water disposal wells, which are tied to the oil and gas industry, could be related.
More research would be needed, Williams said.
"We can't rule out the possibility of a larger earthquake," he said. "We don't know the chances for it, but we have to consider it as a possibility."
Dallas County Judge Clay Jenkins sent out a memo on earthquake preparedness Wednesday morning, reassuring residents that the county uses an "all-hazards approach" for earthquake planning and urging residents to create an earthquake preparedness kit, and to "drop, cover and hold on" in the case of more shaking.