Residents of Northern Nevada and the Lake Tahoe basin were rattled on Monday by an earthquake that struck southeast of Reno, Nev. Preliminary estimates showed that the quake occurred at 3:08 p.m. and had a magnitude of 5.5, according to the U.S. Geological Survey.

It struck during what experts say could be a period of increased seismic activity in the region, after decades of relative quiet. But its occurrence does not signal that a larger, catastrophic quake is any more likely.

An earthquake with a magnitude of 7.0 struck off the coast of Northern California last week, causing little damage but setting off a tsunami warning that affected five million people.

Seismologists have long warned that an overdue “Big One,” the likes of which California has not experienced since 1906, could happen at any time. They have urged residents to prepare as much as possible by assembling emergency supplies and practicing “drop, cover and hold on” exercises with their children.

It has been three decades since a significant quake struck the region.

The Loma Prieta earthquake, with a magnitude of 6.9, shook the Santa Cruz Mountains in California in 1989, leaving 63 people dead and more than 3,700 people injured.

A magnitude 6.7 quake in the Northridge neighborhood of Los Angeles in 1994 left 60 people dead, about 7,000 injured and more than 40,000 buildings damaged. The catastrophe also revealed a major defect in some steel-frame buildings, including many high rises, which under extreme shaking could collapse.

This is a developing story. Check back for updates.