13 aftershocks have followed last week’s Sparta earthquake. Could more be coming?
Aftershocks have continued all week following last Sunday’s 5.1 magnitude earthquake near Sparta. The most recent was felt Saturday morning, the 13th aftershock since North Carolina’s strongest quake in a century.
But what exactly is an aftershock? National Earthquake Information Center geophysicist Don Blakeman says it’s just an earthquake by another name.
“There really isn’t a distinction, aftershocks are just earthquakes,” Blakeman said. “Aftershocks aren’t special. Therefore they’re not any more dangerous than any other little earthquake.”
Blakeman said earthquakes are usually arranged by how strong they are and when they occur. The strongest earthquake in a series is the mainshock, which is preceded by foreshocks and followed by aftershocks.
The United States Geological Survey, which tracks and studies earthquakes, says mainshocks are usually followed by numerous aftershocks.
Last Sunday morning’s 5.1 magnitude earthquake was the strongest North Carolina has seen since 1916. It was centered near the county seat of Allegheny County in the northwestern part of the state, just south of the Virginia state line and could be felt for hundreds of miles.
Blakeman said the Sparta quake is notable for being the strongest in the Eastern United states since the 2011 5.8 magnitude earthquake in Virginia.
“That’s what’s remarkable about it,” Blakeman said of the Sparta quake. “It’s a good sized quake, and we don’t get these very often.”
What’s also unusual about the Sparta earthquake is that it hasn’t been followed by sizable aftershocks, Blakeman said.
“With a 5.1 magnitude quake, we’d expect one or two aftershocks of 4 or larger,” Blakeman said. “But we haven’t seen that yet.”
There have been 13 aftershocks around Sparta since last Sunday. The strongest measured 2.9 magnitude, and the most recent was a 2.1 magnitude quake Saturday morning.
Quakes of that magnitude are strong enough to be felt by some people but not damage buildings the way last Sunday’s quake did.
Because there haven’t been sizable aftershocks so far, Blakeman mentioned the remote possibility that the Sparta quake could be a foreshock to a stronger quake.
In rare instances, Blakeman said, strong earthquakes can occur before even stronger ones. But Blakeman doesn’t expect that to happen in this case.
“There’s the very slight possibility that there could be a larger quake,” Blakeman said. “Statistically that’s not likely. But since we can’t predict earthquakes, we can’t say there won’t be a stronger one. Just that there probably won’t be.”
Aftershocks don’t pose any greater threat than stronger earthquakes, Blakeman said, and may offer opportunities to practice safety measures.
“The only thing anyone can do about earthquakes is practice preparedness,” Blakeman said. “Follow the rules, makes sure the water heater is secured, practice what you’re going to do when earthquakes happen. If people feel a little more in control, I think it helps them not worry about future quakes.”
