(Bloomberg) -- 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 to insurance broker Aon Plc.

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 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% in 1996 to roughly 10% 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.”

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