Seismologists say fault line will continue to slip in Napa

NAPA, Calif. (KGO) -- For the first time, scientists say they have forecast the shifting of ground in a residential area after an earthquake.

They say the fault that caused the 6.0 earthquake in Napa this summer will move several more inches in the next three years.

In a photo of a winery you can see half-way up the slope, where the color is darker on the left, how the ground is out of alignment.

ABC7 News visited one of the neighborhoods that sits on the fault line. Neighbors say the large crack in the street has only gotten bigger since August and believe they're already feeling effects from the afterslip.

"I could do without an earthquake again," resident Barbara Caligiuri said.

Regardless, the Napa quake is still impacting people like Caligiuri, who lives in Napa's Browns Valley neighborhood.

According to Ken Hudnut, a geophysicist with the U.S. Geological Survey, there's an afterslip -- where there's still movement on the fault.

"At the time of the earthquake, the movement on the fault is sudden, and then there's this continuing movement that goes on. Initially, that's fast, but then it slows down with time," Hudnut said.

He describes the friction like the slow smearing of clay. Hudnut expects the ground to slip between two and six inches in the next three years. The results could mean more structural damage to at least 20 homes near the fault line, in a neighborhood hit hard by August's 6.0 earthquake.

"You can see additional cracking where the fault that went right through the dirt, right through the street here, looks like it is moving or pulling up," resident Jim Pederson said.

Pederson who lives just feet away from the fault line says he isn't surprised there's still movement. There are cracks in the road, PG&E had to replace a gas line, and just this week, a neighbor's power went out. But the thought of this slow shift lasting for several years concerns him.

"I hope he's wrong. That much movement. A couple of these houses on the fault line have some damage where the ground moves sideways," Pederson said.

Hudnut says there are ways to mitigate the hazard from an afterslip, but it's pricey. The best thing to do is get a stronger and stiffer foundation on your house.