HILLSBOROUGH, N.C. (WNCN) — A loud boom heard and felt in Hillsborough late Thursday morning was an earthquake, the United States Geological Survey has confirmed with CBS 17.
“We heard a huge noise. It sounded like something fell on the building and the whole building shook,” a 911 caller told dispatchers in the moments after the incident.
According to Thomas Pratt, a research geophysicist with the USGS, the magnitude 2.2 quake didn’t initially register, but further analysis showed it was an earthquake.
The USGS earthquake map shows the epicenter of the tremblor was near Arbor Lane in Hillsborough, just south of the interchange between Interstate 40 and Interstate 85.
It’s estimated the earthquake occurred at a shallow depth of 5.4 kilometers, or 3.3 miles, but Pratt said the margin of error in that estimate is plus or minus two miles.
Pratt said that because the location of the earthquake was next to a mine, it was initially thought to be a mine blast. Their computer algorithm didn’t pick it up either.
“It’s right next to a quarry that you can see on Google Earth and so the analyst initially dismissed it as potentially a quarry blast and it’s not until we re-examined it this morning that we felt it really is an earthquake,” Pratt said.
So what’s is to blame for the noise accompanied with the shake? Pratt said the quake’s shallow depth sent soundwaves to the surface, creating the reported “boom” sound.
“It’s fairly common. People describe these as kind of like cannon booms or cannon shots, things like that. That’s a pretty common analogy people make with these small earthquakes,” Pratt said.
Callers to 911 and dispatchers were equally at a loss for what the noise and vibrations were.
“I’m at Duke primary care. Our entire building just shook…Should we evacuate our patients from the building?” asked one caller.
“Ma’am at this moment, we don’t know where it came from. We don’t know what it is so I can’t advise,” a dispatcher answered.
Small earthquakes are not uncommon — Pratt said there could be a few dozen a year in North Carolina — but don’t often register on measuring scales.
The boom was felt in several parts of Orange County, with more than a dozen reports to officials about noise, shaking and rattling buildings.
Pratt said it’s unlikely geologic investigators will examine this earthquake like they do for larger magnitude incidents. Because they often happen in clusters, there is a chance for more earthquakes to follow.
“The chances that it would be something much larger are very, very small. So, I wouldn’t worry too much about it,” Pratt said.