The 6.0-magnitude earthquake that shook California’s Napa Valley early Sunday morning was the biggest temblor to hit the area since 1989, but trends show another -- larger -- quake may be on its way. "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 coming in the next week, according to the Northern California Seismic System report.
