Scientists have made an important advance in their efforts to predict earthquakes, the journal Nature says.
A team of US researchers has detected stress-induced changes in rocks that occurred hours before two small tremors in California's San Andreas Fault.
The observations used sensors lowered down holes drilled into the quake zone.
The team says we are a long way from routine tremor forecasts but the latest findings hold out hope that such services might be possible one day.
"If you had 10 hours' warning, from a practical point of view, you could evacuate populations, you could certainly get people out of buildings, you could get the fire department ready," said co-author Paul Silver of the Carnegie Institution for Science, Washington.
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