The western United States is overdue for a huge earthquake and tsunami and is nowhere near ready to cope with the disaster, experts say.
A volatile, horseshoe-shaped area known as the Pacific Ring of Fire has recently erupted with quakes in Chile, Japan, Mexico and New Zealand, and seismologists say it is just a matter of time before the next big one hits.
Twin fault lines place the US west at risk: the San Andreas fault that scars the length of California and the lesser-known but more potent Cascadia Subduction Zone off the Pacific Coast.
A 9.0 quake in this underwater fault that stretches from the northern tip of California all the way to Canada's British Columbia could simultaneously rattle the major port cities of Vancouver, Portland and Seattle, unleash a massive tsunami and kill thousands of people.
"From the geological standpoint, this earthquake occurs very regularly," says engineer Yumei Wang, who is the geohazards team leader at the Oregon Department of Geology.
"With the Cascadia fault, we have records of 41 earthquakes in the last 10,000 years with an average of 240 years apart. Our last one was 311 years ago so we are overdue," she says.
Records from the last Cascadia quake in 1700 AD show that the tsunami it generated was so powerful that it killed people in Japan.
"Geologists can't predict exactly when the next earthquake will be but engineers can predict the damage pattern," says Wang.
Buildings at risk
Major efforts to retrofit buildings have been underway for decades in western states, but many coastal schools, hospitals and fire and police stations are still housed in older buildings and remain at risk.
"Eight hundred and four of our schools out of 1355 schools - more than half of them -- e think have a high likelihood of collapse in a major earthquake," she says, referring to the state of Oregon.
In the case of a tsunami, experts are also concerned about old structures and elderly or ill people who may live near the water and may be unable to escape a swelling wave.
"Quite frankly some of our coastal communities are extensive enough and flat enough that moving inland and uphill is not possible. It is just too far to go," says Wang.
Engineers have devised a concept for a tsunami shelter where residents could seek higher ground without travelling far inland, but none have yet been built for public use.
"All preparedness is local and it varies dramatically over the length of the coast," says Tom Tobin, president of the Earthquake Engineering Research Institute.
For instance, California has a state law that says all hospitals should be constructed so that they can withstand a major earthquake and still function, says Tobin.
But "since 1971 only one new hospital has been constructed in San Francisco to that higher standard. All the other campuses are in older buildings, some of them dating back to the early 1900s," he says.
Other big risks include damage to the electricity grid and the potential for a quake to upset Washington state's shuttered but volatile Hanford nuclear plant which holds more than 200,000 cubic metres of radioactive waste and is considered the most contaminated nuclear site in America.
"We are just not ready," says Ivan Wong, principal seismologist and vice president at URS, a large international engineering firm.
"We are not at all even close to being as prepared the way the Japanese were, and yet you can see the devastation that occurred," he says.
"I think in the United States we have a hard time convincing people there is a real danger that lies out there on the Pacific northwest coast."
Every earthquake behaves differently
Even though the quakes along the Pacific Ring of Fire may seem to be happening more regularly, scientists say they have not been able to identify a pattern and the quake in Japan does not necessarily make the United States more vulnerable.
"As far as we know, an earthquake ... in Japan does not have an effect on any occurrence of earthquakes ... say, in California, or any other parts. The main effect it would have is to the adjacent parts, to the north and to the south of that area," says Jim Whitcomb, geophysicist at the National Science Foundation.
Wong says the next big US quake could be preceded by a foreshock, like the 7.2 one in Japan that came days ahead of the 9.0 event on Friday, or it might come with no warning at all.
"Every earthquake seems to behave in a very different fashion," he said.
But, he describes the Japan quake as "the best analogue for a large earthquake that could strike the United States in terms of what the effects of the Japanese earthquake were on the modern infrastructure."
"I think there are a lot of lessons that we could learn."