A magnitude-5.1 earthquake struck the Los Angeles area Friday night, jolting nearby communities and breaking water mains in some neighborhoods.Its epicenter was in Orange County, one mile east of La Habra and four miles north of Fullerton, the U.S. Geological Survey said.

Shortly after the earthquake, nearly two dozen aftershocks followed.

A magnitude-4.1 shake rattled the area Saturday afternoon, centered about a mile and a quarter southeast of the Los Angeles County community of Rowland Heights, the geological agency said.

After the Friday night earthquake, authorities said police and local fire departments assessed affected areas and found no damage or significant injuries. One minor injury was reported in Orange County, emergency officials said.

“Tonight’s earthquake is the second in two weeks, and reminds us to be prepared,” Los Angeles Mayor Eric Garcetti said.

An hour earlier, a magnitude-3.6 tremor struck the same area, according to the U.S. Geological Survey.

The quakes come on the heels of a magnitude-4.4 tremor that hit near downtown Los Angeles a week ago. It shook nearby buildings but did not cause significant damage.

Southern California has experienced relatively minor tremors since 1994 when a magnitude-6.7 quake killed dozens and caused $42 billion in damage. It now stands as the second-costliest disaster in U.S. history, after Hurricane Katrina.

Earthquakes with less than magnitude 5.5 don’t usually cause significant damage or casualties, though results vary by region, geophysicist Paul Caruso said.

Damage often depends on construction codes and types of rock that exist underground, he said.