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Earthquake

Seismic Waves and Earth's Interior

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The lines represent P-waves radiating out from the earthquake. The different colors of the lines represent the velocity of the waves: Note that the lines turn blue as they cross the Moho, because they speed up.

A flat line in the seismograph means that the ground is stable. When the P waves arrive from an earthquakes, there are large squiggles in the seismograph.

Karlovac Seismograph

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Swipe to control animation

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Kupa Valley

Zagreb Seismograph

Karlovac Seismometer

Mantle

Zagreb Seismometer

This animation simulates what Andrija Mohorovičić observed in 1909. Click on Earthquake to start the simulation. Roll your mouse over or tap the animation for more explanation.

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Crust

A seismometer is an instrument that records movement of the ground beneath it. Early models (like this one) had a spool of paper and a suspended pen that drew a seismograph, shown below.

Mohorovičić discontinuity (Moho)