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Australian scientists may have found a practical way of predicting earthquakes using space-based radar interferometry to map ground movement. However, they are not the only ones offering hope after the Sichuan earthquake. Scientists in Britain, Taiwan and the US, are proposing an earthquake warning system based on electrical disturbances that precede quakes on the ground below.

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LinLin Ge and co-workers at the University of New South Wales have mapped the movement of the ground caused by the Sichuan earthquake using space-based radar interferometry. They have been using data from JAXA's PALSAR instrument on board the Diachi satellite, supplied by the Earth Remote Sensing Data Analysis Centre (ERSDAC) in Japan.

Scientists at the University of NSW have mapped the movement of the ground caused by the Sichuan earthquake in China using space-based radar interferometry. They have used predicted orbit data to deliver a result in 17 hours and 46 minutes. ALOS PALSAR. Copyright METI and JAXA [2008] by ERSDAC, Japan. DInSAR processing by CRCSI / UNSW / NSW Lands, Australia.

The researchers call the technique differential satellite radar interferometry (DinSAR). They have used it to map movement along the entire 300-km earthquake fault.

While it is useful to monitor the exact extent of the earthquake, the technology would be even more valuable if it could be used for earthquake prediction. This may be possible.

Earthquakes occur because stress in the Earth's crust is not released. This stress causes the crust to deform immediately preceeding the quake. DinSAR is accurate enough to detect this movement.

In Britain, Taiwan and the US, scientists have also been working on the question of whether remote sensing can be used to detect earthquakes. Taiwanese researchers say they have found a close link between electrical disturbances on the edge of the atmosphere and impending quakes on the ground below.

Jann-Yeng Liu from the Centre for Space and Remote Sensing Research in Chung-Li looked at over 100 earthquakes with magnitudes of 5.0 or larger in Taiwan over several decades. The researchers found that almost all of the earthquakes were preceded by distinct electrical disturbances in the ionosphere.

NASA scientists and workers at Surrey Satellite Technology in the UK have proposed a way to use the effect in an earthquake warning system. Stuart Eves, head of business development at the company, told BBC News: 'The evidence suggests we're now crossing the boundary in terms of technology readiness.'

He added: 'What we don't know is how big the effect is and how long-lasting it is before the earthquake.'

NASA's Minoru Frieund developed the scientific theory behind the effect. The idea is that when rocks are compressed – such as when tectonic plates shift – they act like batteries, producing electric currents.

When these currents reach the surface, it becomes positively charged. This charge can be strong enough to affect the ionosphere.

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