An earthquake that struck the California wine country north of San Francisco and flooding in the U.S. last month caused more than $4 billion in economic losses, according insurance broker Aon Plc. (AON)

A 6.0-magnitude temblor shook the city of Napa on Aug. 24, damaging more than 1,100 buildings, injuring at least 258 people and causing about $2 billion in economic damages, the London-based broker said today in a report. Insured losses are expected to be in the hundreds of millions of dollars, because of the below-average extent of coverage, Aon said.

“Residential earthquake insurance penetration rates have gradually lowered in California during the past two decades from 33 percent in 1996 to roughly 10 percent today,” Steve Bowen, associate director and meteorologist for Aon Benfield Impact Forecasting, said in a statement. The Napa quake “serves as a reminder of the unpredictability and costly impacts.”