Carolyn McPherson lies beside the little seismometer that has sat on the floor of her Charlottesville home for two years. Last week, the device finally came to life. (Norm Shafer/FOR THE WASHINGTON POST)

For geology nut Carolyn McPherson, last week’s earthquake was “better than Christmas.”

For two years, a tiny seismometer on the floor of McPherson’s basement laundry room in Charlottesville sat inert next to a stack of boxes crammed with rocks and fossils. The matchbox-size white plastic box recorded nary a tremble.

But at 1:51 p.m. Tuesday, the seismometer sprang to life as a magnitude-5.8 quake shuddered across the region. When McPherson and her husband, Mike, checked their computer, they saw what she called a “nice set of tracings”: spiky blue, green and yellow lines displaying the earthquake’s jostling in three dimensions.

“We let out a cheer,” said McPherson, 65, a retired English professor, who added that she would have felt differently in the end if the quake had caused more damage.

Via McPherson’s computer, the device sent a signal to Stanford University, where seismologists reviewing the data declared it a winner: Of more than 1,000 home seismometers tied into Stanford’s national network, hers was the closest to the epicenter, some 30 miles distant.

Four other home seismometers in the region also recorded the quake.

They’re all part of the Quake-Catcher Network, a “citizen science” project that’s distributing the tiny seismometers. The goal: a dense mesh of inexpensive detectors to augment the much sparser network of research-grade seismometers deployed by the government, which can cost $100,000 each.

“If we have more sensors, we can, in theory, detect earthquakes and characterize them before they hit surrounding areas,” said Jesse Lawrence, a Stanford seismologist who helps lead the Quake-Catcher Network.

Lawrence hopes the project will eventually help first responders in a huge, damaging quake by directing them toward places prone to more-severe shaking. As the sensor network records smaller quakes, it can slowly sketch a picture of more-vulnerable areas.

Seismologists have just begun to get a handle on this phenomenon, called micro-zoning, said Elizabeth Cochran, a geophysicist at the U.S. Geological Survey in Pasadena, Calif. Variations in the geology underlying a region can shake one building severely while another just a few miles away experiences far less movement.

“You could potentially use the information to know which areas of the ground will shake,” said Cochran, who dreamed up the network in 2006.

That’s when laptop computers first appeared with embedded accelerometers, tiny devices to detect motion. Ever on the lookout for more data — especially on the cheap — Cochran dreamed of laptops everywhere pouring Earth-shaking data into a central server.

It turned out, however, that people jostle their computers far too often for laptops to be of much use for the project. So the team switched to the home seismometers, which cost about $50 apiece and plug in to desktop computers. Some 1,000 to 2,000 are now deployed, with another 6,000 poised to go, purchased with a $1.8 million grant from the National Science Foundation. Half will go to classrooms, where kids will no doubt delight in watching squiggles appear on computer screens as they bang tables and slam doors.

Most of the other 3,000 will be shipped to volunteers in quake-prone zones in California and Missouri, where the New Madrid fault ripped off huge quakes in 1811 and 1812.

With just five of the home sensors in Virginia and the District, Lawrence said, last week’s quake didn’t generate enough data to be of much immediate use. But it did prove that the network can deliver data as designed.

For McPherson, the rumbling reinforced a love of geology that stretches back to when she was 10 and first read about the enormous plates of rock that gird the Earth and crash into each other. “Geology wasn’t just looking at old rocks,” she said of her tectonic epiphany, which was shaken loose by an issue of Scientific American. “There’s stuff inside the Earth that’s active.”

For decades, McPherson poked around famous paleontological sites in Arkona, Ontario, and the Joggins Cliffs in Nova Scotia, collecting fossilized trilobytes, sponges and leaf imprints as her husband “sat in the car and read a book.”

The patient spouse was paying attention, though. Two years ago, a Google search pointed him to the Quake-Catcher Network and the perfect birthday gift: a seismometer of her own. “If you didn’t know Carolyn, you’d think it would be like buying her a dishwasher or a chain saw — a typical guy mistake,” said Mike McPherson. Instead, “she was delighted.”

Earthquake tracing in hand, Carolyn McPherson now has another weapon in the geological arsenal she deploys to inspire her 12 grandchildren. It’s a nice contrast to the coprolite — a hunk of fossilized dinosaur poo — she recently gave her 4-year-old granddaughter.

“I’m going to put it on T-shirts,” McPherson said. “I’m just so proud of myself.”