A "major seismic hazard" under San Diego could damage 120,000 buildings, cost $38bn and make thousands homeless, earthquake experts have warned.

The Rose Canyon fault runs through the heart of downtown San Diego - but its potential danger is said to have been underestimated.

A 6.9-magnitude quake could swamp emergency services, spark "hundreds of fires", displace 36,000 households and destroy many buildings.

"An earthquake originated on this fault may produce substantial damage and losses for the San Diego community," says the Earthquake Engineering Research Institute.

Image: Tens of thousands could be displaced in the San Diego area, where more than three million live

Researchers spent five years studying the likely effects of a tremor and say roads, bridges and many older buildings could be devastated.


The airport, old town and downtown San Diego could suffer "major geologic ground failure and ground shaking hazards resulting in severe seismic damage consequences", says the report.

Liquefaction - where soil behaves like a liquid - and landslides and aftershocks are also possible.

The report warns of "widespread damage to buildings, including moderate to severe damage to approximately 120,000 of the nearly 700,000 structures countywide".

It says damage to buildings and infrastructure is "estimated at more than $38 billion".

Emergency services are also likely to be overwhelmed, says the report - put together by experts in geoscience, engineering and emergency management.

It warns: "Emergency responders will need to respond to tens to hundreds of fires following the earthquake and should expect to be handicapped by loss of water service and access roads, particularly in coastal communities."

The city's airport would also likely be badly affected - a section of the fault passes right under the runway.

The damage is predicted to be significant because many buildings were built before the danger posed by the fault was fully realised.

"Older, highly vulnerable structure types will be hardest hit, causing extensive damage, many building losses, and many possible casualties," say the experts.

Most older buildings have not been adapted to make them more quake-resistant.

The best estimates put the chance of a magnitude 6.7 or larger quake in the area in the next 30 years at 18%.

The report says planning is "imperative to avoid potential disaster" in the San Diego area - which has a population of more than three million.

It calls for the setting up of a Seismic Resilience Working Group and has produced an 11-point plan to advise local authorities and emergency services.