Using data from over 40,000 earthquakes over the past 40 years scientists have produced the first three-dimensional image of the Earth's entire structure, from its outer crust to its deep inner core.

Scientists from the Center for Computational Seismology at the Lawrence Berkeley National Laboratory in California have used one of the worlds most powerful computers, a Cray T3E, to analyze the speed of shock waves produced by earthquakes.

They measured the time the waves took to get from the epicenter of the earthquake to seismographic stations located around the world. The Cray computer allowed the velocity of the shock waves to be calculated at various depths inside the Earth.

The image shows the speed at which seismic waves travel through the Earth's liquid iron core. Yellow areas indicate the slowest velocity, blue the highest.

"What we did is sort of like performing a CAT scan on the planet," said Don Vasco, one of the scientists involved.

"Just as a CAT scan uses thousands of rays to characterize a part of the human body, we used thousands of waves to characterize the makeup of the Earth."

The Lawrence Berkeley National Laboratory.

The radius of the Earth is 6,378 km (3,963 miles). It is divided into several sections. The outer part is called the lithosphere which consists of the outer crust and the upper mantle stretching about 100 km (62 miles) beneath us. Below that is the mantle which goes down another 2,800 km (1,740 miles) to the Earth's core which is itself divided into the inner and outer core.

The scientists have found evidence that the outer core is not smooth as has long been suspected. This research will help in the understanding of the Earth's magnetic field which causes a compass to point north-south.

There is however a long way to go.

"Nobody knows for certain how the Earth works," said Don Vasco.
 

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