Napa, California quake insured losses probably less than US$250 million: RMS

Risk Management Solutions Inc. announced this week it estimates insured losses from the recent earthquake in California “will not exceed” US$250 million.

On Aug. 24, the South Napa Earthquake, measuring 6 on the Richter scale, struck about 50 kilometres north of San Francisco. It was the “largest” earthquake affecting the San Francisco Bay in 25 years, noted the United States Geological Survey. On Oct. 17, 1989. the Loma Prieta quake – centred about 100 kilometres south of San Francisco – killed 63 and caused up to $10 billion in losses, according to USGS.

After last month’s South Napa quake, CoreLogic EQECAT had estimated insured losses could range from US$500 million to US$1 billion. At the time, EQECAT said there was “a fair amount of uncertainty” on business interruption and contents losses.

But RMS said Sept. 2 that most of the affected businesses re-opened within a week.

“Most area wineries were impacted in some way – primarily by storage barrel damage – but are now open for business,” RMS stated, adding the “primary damage was due to ground shaking with minimal observations of fire following earthquake or earthquake sprinkler leakage.”

There was “little liquefaction or lateral spreading observed,” RMS noted.

RMS added the “majority of severely damaged unreinforced masonry structures” were in downtown Napa.

The epicentre was about 13 km from Vallejo, USGS reported.

“In Vallejo, older buildings and historic structures – generally those constructed before seismic design principles were adopted – sustained much of the damage,” RMS said. “In regions further afield, such as downtown Sonoma and Yountville, damage was limited. A few high-value losses took place, including structural damage to a monastery in Oakville.”

USGS noted the quake, on the shore of San Pablo Bay, was between the Hayward-Rodgers and Concord-Green Valley fault systems, which are part of the San Andreas Fault system, which forms the boundary between the Pacific and North American tectonic plates.

“The persistent northwestward movement of the Pacific plate relative to North America primarily causes right-lateral slip across the major faults, but also causes deformation between the major faults,” USGS says.

In a 2008 study published by UGSC predicts the probability of an earthquake of magnitude 7.5 or greater in the next 30 years is 46%.

In the 1989 Loma Prieta quake, forty-two deaths were caused by the collapse of an elevated highway, USGS noted.