Scientists in the United States say they have devised a technique that could one day help predict earthquakes.
Scientists measured stress-induced changes in the Earth's crust before and after two small quakes deep in the San Andreas Fault in California.
They found a big change in the stress level in the crust 10 hours before one of them, which they say is likely to signal a coming tremor.
Their findings have been reported in the journal Nature.
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, in Washington.
"Hurricane [warnings] give you an idea of what could be done." he told the BBC.
The new work comes out of the San Andreas Fault Observatory at Depth project which has been set up in Parkfield, a tiny rural town halfway between Los Angeles and San Francisco.
The town experiences small to moderate-sized quakes at regular intervals as the Pacific and North American tectonic plates grind against one another along the San Andreas Fault.