Northern California is overdue a massive earthquake that would topple buildings, rupture water and gas pipes, and cripple transport and communications systems, scientists have warned.
They are concerned about the Hayward Fault, which runs through Oakland on the east side of San Francisco Bay. There are fears that a 7.0 magnitude earthquake along this fault - a scenario outlined in the recently published HayWired report – would “devastate” infrastructure, leaving residents in the Bay without water for up to six months.
The HayWired report, produced by the US Geological Survey (USGS), outlines a “hypothetical yet scientifically realistic” depiction of the events which would follow a huge tremor on the Hayward Fault.
On average, for the past 12 major earthquakes on the fault the interval has been about 150 years, give or take 60 years, the report says. The last major event was 150 years ago, leading scientists to conclude that a major tremor is imminent.
California-based risk mitigation expert Ronald Eguchi told New Civil Engineer that one of the biggest risks would be to the water supply. The average east-Bay resident would lose water service for six weeks and some for as long as six months, the report says. It also predicts about 450 large fires that would result in $30bn (£21.8bn) loss.
“These water networks are very old and it’s impossible to go back and retrofit these systems with earthquake resistant pipe, so you’re going to have a lot of damage which would lead to disruption of service,” Iguchi said.
“If you haven’t got the water to fight the fires then you have a situation where the losses from the fire following effects could be very devastating.”
San Francisco tried to prepare for damage following an earthquake in 1906 by the creation of an auxiliary system designed to pump sea water from the Bay if the municipal system failed.
“If I were to look at the priorities I would probably say water, transportation, communication, then you’ve got power, gas and sewage,” Iguchi said.
“If you’re speaking about life lines and infrastructure, all of these systems are very critical – you can’t look at one lifeline system by itself you have to look at all of them together.”
The report predicted that even if all buildings in San Francisco Bay complied with building codes, 0.4% could collapse, 5% could be unsafe to occupy and 19% could have restricted use.
“The unique feature of this fault is that it traverses through a highly dense urban area,” Iguchi said.
“Because the shaking is going to be very severe and you will potentially have ground failure effects I think the damage will be quite devastating.”
He added: “If you have very, very large earthquakes you can’t mitigate against all the damage. What you hope for is that you minimise the safety problems and the hazards.”