Bigger than 'the big one': threat to US of linked quakes revealed

Warnings about "the big one" - a huge US earthquake that could devastate cities - have stoked fears across the country's west coast for decades.

- Gabrielle Canon

But according to a new study, a high-magnitude quake in the Pacific northwest could set off a secondary quake on California's San Andreas fault, causing an unrivalled catastrophe.

"The bigger one" would have the potential to wreak havoc up and down the coast, researchers say. "We could expect that an earthquake on one of the faults alone would draw down the resources of the whole country to respond to it," said the study's lead author, Dr Chris Goldfinger, a marine geologist and geophysicist.

"If they both went off together, then you've got potentially San Francisco, Portland, Seattle and Vancouver all in an emergency situation in a compressed timeframe."

The Cascadia subduction zone, which can produce earthquakes of magnitude 9 on its own, has triggered tremors on the San Andreas fault in the past, according to the study, published on 29 September.

Goldfinger said the findings had come after decades of head-scratching and a lot of data that was difficult to explain.