Geoscience Reference
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of the Nimitz freeway had partially collapsed and rescue workers were trying to free motor-
ists trapped underneath. The huge concrete slabs were unstable and aftershocks could have
sent them crashing down. The focus of the earthquake was almost 100 kilometres away, so
sensors on the fault itself could radio a warning at the speed of light which would reach the
rescuers 25 seconds ahead of the shock waves themselves, travelling at the speed of sound,
giving people time to scramble clear. In the future, such a system could be used to give
a brief warning of the main shock of an earthquake. For example, shock waves from the
main fault lines behind Los Angeles would take up to a minute to reach the city. A radioed
warning would not be enough for evacuation but, linked to computer systems, it could help
banks to save their accounts, elevators to come to a standstill and open their doors, auto-
matic valves to seal off pipelines, and emergency vehicles to get clear of buildings.
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