Various some waves

Decades ago, seismologists noticed that records from an earthquake changed once the event was a certain distance away, aproximately 105 o in terms of the angle between the quake and the seismograph at the center of the Earth. After such a distance, waves disappeared almost completely until the slow surface waves arrived. The area beyond 105 o forms what is called a SHADOW ZONE . At greater distances some P waves would arrive but no S waves. From this, researchers determined the Earth's core is fluid and moltne. This explains the lack of S waves in the shadow zone and the bending of P waves to form their own shadow zone.
This is just one example of how seismic tomographers used data concerning seismic waves to map the Earth's inside.

Most curricular materials in TeachEngineering are hierarchically organized; . , most hands-on activities are part of lessons , lessons are grouped into multiday curricular units and these again are bundled into subject areas .

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