After an earthquake shook the East Coast on Tuesday, many people reached for their cellphones and tried to call loved ones. And many couldn't get through — but it wasn't the earthquake's fault.
No damaged cell towers or wires were reported by the major mobile carriers following the quake, which struck just before 2 p.m. EST and registered a magnitude of 5.8 at its epicenter in Virginia.
So what caused the problems?
Too many people using their phones at once, overloading the cellular networks.
"You have X amount of bandwidth and once you have a sufficient amount of data trying to get through that bandwidth, it overwhelms the system," says Hal Cohen, an emergency response expert at Witt Associates in Washington. The firm is run by James Lee Witt, who ran the Federal Emergency Management Agency during the Clinton administration.
Today's problems come just weeks before the 10th anniversary of the Sept. 11, 2001, terrorist attacks — after which there were major upgrades to telecommunications networks nationwide in a bid to guard against outages during disasters or another attack. Cohen says even a minor incident, as Tuesday's earthquake turned out to be, underscores the continued vulnerability of communications networks.
"Any emergency plan that says 'we're going to rely on a cellphone system' is not an emergency plan," Cohen says. "Good emergency planning essentially assumes the failure of one or more channels of communications and is going to rely on multiple means."
Verizon Wireless spokesman Melanie Ortell said the company has found no damage to its network, "which was built for reliability in situations like this." Ortell added that "there was significant network volume for some customers in parts of the East for about 20 minutes after the tremor ... everything returned to normal quickly once the tremors ended."
However, a number of Verizon Wireless customers in the Washington area — including many at the NPR headquarters — reported their service interruptions continued an hour after the quake.