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If you live in California, you will know that the Big One is coming: a powerful earthquake of magnitude up to eight is heading for the state. Energy has been growing along the San Andreas Fault for more than a century. Nobody knows exactly when and where, but that day, that energy will be released.
It could hit the heart of San Francisco, devastated for the last time by a Big One in 1906. Or maybe it would cross southern California like the magnitude 7.9 earthquake that struck in 1857 and broke some 225 miles from the San Andreas Fault.
More than 100 years later, it's hard to predict exactly how tough the next Big One will be. John Vidale, director of the Southern California Earthquake Center and associate professor at the University of Washington, said: Newsweek It will not look like movies. Cities will not collapse in the rubble and tsunamis will probably not spread in California. But without proper preparation, the Big One could "cripple" the finances of a state that has just become the fifth largest economy in the world.
This interview has been modified for its length and clarity.
What's a "Big One" and where could such an earthquake happen?
A tectonic boundary between the North American and Pacific plates crosses California. It's a big flaw where both sides move three or four centimeters a year. The strain accumulates for one or two hundred years along this border, and eventually this strain becomes so large that the fault can no longer withstand it. It breaks and moves about 15 feet at a time, causing an earthquake.
There are three, four, five sections to this fault – and many other parallel flaws – but we worry about a Big One striking north or south of San Andreas. There is a part between north and south of central California that seems to act as a buffer. There is a chance that the break-up will be end-to-end, but we think it is unlikely or does not happen.
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How often do these massive earthquakes occur?
It's all a few hundred years old. The earthquakes that have occurred in the meantime are still devastating for a local area, but instead of the magnitude eight, they are more like the magnitude seven. It's a logarithmic scale, so an eight is about 30 times more energy than a magnitude seven.
Small earthquakes do they not help to dissipate some of the energy accumulated in the basement?
These small earthquakes release only a tiny amount of energy compared to larger ones. It would take 10 magnitude seven earthquakes to let out the strain of magnitude eight. We do not have many, so these little earthquakes do not slow down the big ones.
Does this mean that the next big is inevitable?
This is true. When we look at the history of the fault, we can see that these great earthquakes have occurred several times over the past millennia, so yes, it's inevitable. We simply do not know if it will be now or in two hundred years.
What kind of impact would a Big One of Northern or Southern California have?
The impact of the far north would be huge – I mean the San Andreas crosses San Francisco. It is much closer to San Francisco than to Los Angeles.
Downtown San Francisco is vulnerable – some of the older buildings survived the 1906 tremor, but that does not mean they will be safe in the next earthquake. Many buildings are built near the fault and on soft ground that may liquefy.
A Big One South would probably be a little further away from the heart of Los Angeles, so the impact could be smaller. On the other hand, Los Angeles has many more things to break than San Francisco. So I think the net expectation is similar to north and south. The fault is farther in the south, but it is also more mature, more ready, than that of the north.
More generally, there are many disasters due to an earthquake. This would certainly cause landslides and, presumably, spills of chemicals. We are also concerned about fires.
What about tsunamis?
Tsunamis are not a big problem here. For an earthquake to make a tsunami, it would have to be off, not on the main part of San Andreas. The ground would move laterally, not too vertically, and it's hard to hit a big wave. But many other things could happen.
When the Tohoku earthquake struck Japan in 2011, it caused a catastrophe at the Fukushima Daiichi nuclear power plant. Are there any nuclear reactors in danger of a Big One in California?
Not here – there is one from San Onofre but it has been turned off. There has been a lot of debate about nuclear reactors. Engineers claim that they can secure the reactors, but there have been enough accidents over the years for safety reasons, they tend to no longer build them in most places.
So, how are cities like San Francisco and Los Angeles prepared?
Both cities are among the best prepared for earthquakes in the United States. There are codes for new buildings to make them stronger and more appropriate. We are strengthening inspections, particularly on roads, bridges, ports, airports, hospitals and schools.
The problem is always that fixing problems costs a fortune – we can not just demolish all buildings that have problems and rebuild them. It would paralyze the economy. So we are always taking steps to solve the most serious problems we can afford to solve.
In California, when there is one of these big earthquakes, it will not be like in the cinema: the cities will not turn into rubble. There is damage and death, but the most important problem for a city as a whole will reoccur: the impact on the economy, the cost of replacing buildings and all over again. I mean, it's not as exciting – it does not make big Hollywood movies – but it's the biggest concern.
In other countries, it's different. In China, Turkey or Iraq, the buildings are so bad that it is really terrifying that they all fall around you. The San Andreas expands to Mexico. If the fault stops there, the country will of course have a huge impact.
But in the United States, most buildings will be fine. It is rather the problem of the infrastructure and the restart.
If the infrastructure does not rebound, what effects will that have on California?
It is quite possible that the earthquake causes something that paralyzes the economy for a long time. For example, nobody expected the Fukushima reactor to be a major problem during the 2011 earthquake in Japan. There is always a small risk of very serious unexpected problems.
It is also possible that a large earthquake has less effect than expected. It's very difficult to predict.
The Big One is worrying for the government because it disrupts a vast territory. But for individuals, medium-sized earthquakes just beneath our feet are often the worst threat.
Los Angeles, for example, is full of mistakes and many of them could experience an earthquake of magnitude seven. A magnitude of seven on a smaller foul could do more damage than the Big One on the San Andreas. The Big One is only part of the danger here.
So, should California residents worry about a Big One?
This should not be in the minds of people every minute – there are enough things to worry about without fearing earthquakes – but every year people should make sure that they are ready. It means making sure they do not sleep where they are going to fall. This means that you have to make sure that their water heater is attached to the wall so that it does not fall and does not break the gas line. It means a little planning.
Basically, you need to know what earthquakes are and how to respond to them.
How can people protect themselves when they realize that an earthquake has begun?
The advice is to protect your head and your chest by protecting your personal safety. Duck, blanket and maintenance are the usual tips and good advice. If possible, put yourself under a desk or at a table, otherwise be aware of what is falling and make sure you do not fall into the race.
How do scientists work to warn people about earthquakes?
We believe that we could eliminate 10 to 30% of the impact of an earthquake by warning people when the earthquake comes. We continue to look for clues to predict earthquakes – we see suggestions we call "weak correlations" to indicate small changes in danger, but there is no gift on the size of an earthquake even when he has already started.
With early warning systems, people can lean, cover and stand faster, factories can move their machines to make them safer, computer companies can adjust their programs so as not to disrupt financial markets, for example. There are a lot of little things we can do.
We think we can reduce the impact, we certainly can not eliminate it.
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