Nearly 90% of Californian homeowners were without earthquake insurance when a 5.1-magnitude tremor struck on March 28, according to state authorities.

“These events serve as a reminder of the importance of purchasing earthquake insurance, having an emergency plan with adequate supplies for your family and [retrofitting] older homes that may not be tied down to the foundations,” California Insurance Commissioner Dave Jones said.

The quake struck in La Habra, about 32km southeast of Los Angeles. It caused slight damage to some homes, a rockslide in Carbon Canyon and broken water mains. About 100 aftershocks were recorded.

The event followed a 4.4-magnitude tremor on March 17 in Encino, San Fernando Valley, just north of Los Angeles.

Earthquake damage is not covered by home insurance in California, and premiums for separate policies are high.

When the 1994 Northridge quake struck about 40% of homeowners had cover, but many insurers stopped writing it after reportedly paying $US12.5 billion ($13.45 billion) in claims.