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They played the tape in railway stations, school classrooms and offices. More than nine million people in California took part in the annual 'shake out'; an earthquake drill to remind people what to do if the 'big one' hits. The scientists say it's almost certain the San Andreas fault will cause an earthquake measuring higher than a seven on the Richter scale in the next thirty years, and that it's long overdue.

Dr Lucy Jones, a seismologist with the US Geological Survey, says people have to remember the risks: "We've had a rather quiet time in LA for the last 15 years, we haven't had a lot of big earthquakes, that's not going to last and so we need to have ways of getting people to think about it, take responsibility, because a lot of the damage is preventable."

The biggest earthquake on the San Andreas fault in recent history was 1906, which destroyed huge areas of San Francisco and killed thousands of people. More recently, motorway bridges have been brought down, but it's been 18 years since the last major quake. Organisers of the shake out want to remind people their reflex action should be to get on the ground and under a table. More people get hurt, it seems, trying to race outside where the risks are often higher.