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#### 世界上最古老的地震站

Making Artificial Earthquakes with a Four-Tonne Steel Ball

I’m at Wiechert’s Earthquake Observatoryin Göttingen, Germany.

This is the oldest working seismic station,

— earthquake detector — in the world.

But there’s also a more unusual bitof scientific equipment here:

a four-ton steel ball that can

be raised up 14 metres above the ground and then dropped,

because it’s a lot easier

to set up and calibrate an earthquake detector

if you can make the ground shake yourself.

– The equipment we have herestarted to work in 1903,

and it’s still working.

Wiechert was the one who createdthe first real working seismometer.

These things record on smoked paper.

This is ordinary white paper.

We take the flame of a paraffin burner to get soot onto that paper.

We think we are the only ones in the world who are doing that.

Wiechert had a theorythat seismic waves allow you

to look into the inside of our planet.

His assistant, Mintrop, had toprove Wiechert’s theory.

He started to calculate,

and he found out if he takes a ball of about four tonnes

and drops it, then he iscreating a small earthquake,

an earthquake big enoughto check the theory of Emil Wiechert.

– The researchers here a century

ago could create a tiny artificial earthquake and then measure it.

So what? Well,

earth tremors movethrough the ground in two ways.
P波 即主波 会在波前进的方向
The P-waves, or primary waves,compress the ground back and forth

in the direction that the wave is travelling,squeezing it together.

Travelling slightly slower are the S-waves,the secondary waves,

which shear the ground side-to-side.

And those waves behave differently,in duration, and wavelength, and intensity,

depending on the groundthey’re travelling through. So,

if you’re clever,and Mintrop was clever,

then you could set up seismicdetectors all round an area,

create a small artificial earthquake by, say,

dropping a four-ton steel ball,

and use the reflectionsfrom within the earth

to build up a picture of what was below without having to dig.

– This knowledge spreadall over the world.

Mintrop got an invitation to Mexicofrom an oil-drilling company.

They asked Mintrop if he could measure the size of that oil field.

He said,”I don’t know. We don’thave oil fields in Göttingen,”

but he accepted the invitation to Mexico,

and of course he did nottake the ball with him,

because in Mexico he was allowedwhat he wasn’t allowed here.

He was allowed to use dynamite.

And he measured the size of this oil field with incredible accuracy.

He had the not-so-nice nicknameThe Crazy German.

He was running around with bodyguards,hiding his equipment in tents,

because our American friends were very

eager to find out how that works,

because that was thelicence to print money.

– So, 100 years ago, with amuch older release mechanism,

and probably a lot more effort,

that steel ball dropped for the first time

onto what was thenpretty much flat ground.

Nowadays there’s much better equipment for figuring out what’s

under the earth’s surface but, uh,

it’s not quite as dramatic.

– I told you your camera would fall…!- [laughter]

It’s still rolling!