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SEATTLE - When a train goes by you see it, you hear it, you also feel it shake the ground. It doesn't end there. The sheer weight of millions of pounds travels deep down into the ground.

UW Seismologist Paul Bodin watches the impact of the trains on his computer.

Buried alongside the tracks are instruments that measure shaking and water pressure. And he can see that water pressure change even 150 feet underground as the train rolls overhead

It's telling us something about the movement of water, said Bodin.

You've seen this phenomenon yourself at the beach. Part of the beach is dry and part of it is wet. The wet sand is soil saturated with water.

When you step, your weight pushes water out from between the sand grains. When you pull your foot away, the water comes back.

Steve Kramer is a UW Geo Technical engineer, an expert on how the ground supports things like buildings.

A simple experiment shows how an earthquake causes the ground to lose its strength and the building falls over. The ground liquefies.

As big as they are, the trains are tiny when compared to the power of a quake. The instruments will help engineers understand this liquefaction process better.

This has the potential to be a very valuable bit of information, said Kramer.

And as the trains roll, and small earthquakes vibrate through the soil and past the sensors, it's hoped we will know just how much shaking the soil under this part of town can take.

The instruments are part of a permanent installation, and more instruments at the surface will be added later.

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