Hold On Tight: Are Bigger, Badder Quakes On the Way?

BY KEITH WAGSTAFFCalifornia hit with worst quake in 25 years

The 6.0-magnitude earthquake that shook California’s Napa Valley early Sunday morning was the biggest temblor to hit the area since the 6.9-magnitude Loma Prieta quake of 1989. While it knocked out power, woke up sleeping Bay Area residents, sent hundreds to the hospital and damaged barrels and bottles in the region's wineries, this recent earthquake is nothing compared to what could be coming in the future.

"For people in California, the last 20 years or so have been a remarkably peaceful time for earthquakes," Thomas Heaton, professor of geophysics at the California Institute of Technology, told NBC News. "Sometimes, people here forget that they live in earthquake country."

NBC Bay Area: Complete Coverage of the 6.0 Earthquake That Rocked the Napa Valley

Earthquakes tend to come in clusters. That usually means aftershocks. In this case, it could mean big ones — there is currently a 29 percent chance that a magnitude 5 or higher quake will hit in the next seven days, according to Northern California Seismic System (NCSS) probability report.

Even more worrisome: the prospect that the South Napa earthquake (as the U.S. Geological Survey (USGS) calls it) could trigger an even larger quake.

"There is always that possibility," Cecily Wolfe of the USGS Earthquake Hazards Program told NBC News. "It's small, but any time you have an earthquake, the probability of another earthquake goes up."

There is currently a 5 to 10 percent chance of something bigger than a 6.0-magnitude quake is coming in the next week, according to the NCSS report.

Probabilities, however, are the best scientists can do. There is no way to tell exactly when the next temblor might strike.

This earthquake was caused by the West Napa Fault, which sits between two larger faults, the Rodgers Creek Fault to the west and the Concord-Green Valley Fault to the east.

The West Napa Fault is like a "lesser version of the San Andreas Fault," Heaton said, in that it's a strike-slip fault where parts of the Earth's crust move horizontally past each other.

If the San Andreas Fault goes off, watch out. It was responsible for the 1906 San Francisco earthquake, a monster that measured around 7.8 and ended up causing around 3,000 deaths.

To put that in perspective, the 1906 earthquake released more than 20 times the energy of the 1989 earthquake, which released around 20 times more energy than the one that just rocked the Napa Valley.

It's not clear when the next "big one" will hit, but there is a 70 percent chance that something bigger than a 6.7-magnitude temblor will go off in the next 30 years. And when it does, there could be more than wine bottles at risk.

"This was really not that big of an earthquake," Heaton said. "Compared to 1906, it was just a baby."