Page 27 - Super Earth Encyclopedia
P. 27
INSIDE EARTH
The shock waves from an earthquake
Shock waves spread out from the are detected all around the world by
focus of the earthquake like ripples instruments called seismometers.
on a pond. They shake the ground, The way these shock waves
often causing great destruction.
travel through the planet varies
according to their nature and
the layers they pass through.
This has enabled scientists
to work out the internal
structure of our planet.
Earthquake waves
are picked up on
other continents. Shock waves pass
through the layers of
Earth in different ways.
TSUNAMI
Earthquakes beneath the sea can trigger
tsunamis. The most devastating have been
caused by a sudden uplift of the ocean floor rocks
above subduction zones, where one plate of
Earth’s crust is slipping beneath another.
Locked section
Upper
plate
Lower plate
LOCK
Although the lower plate may slide harmlessly
beneath the upper plate, the two plates often
become locked together.
Slow distortion
DISTORT
As the lower plate keeps moving, it drags the locked
section of the upper plate downward. This distorts
UPLIFT the edge of the upper plate, building up tension.
An earthquake can make Tsunami Plate springs
dramatic changes to the pushed up back
landscape. In 1964, a
massive earthquake on the
Pacific coast of Alaska lifted
this shipwreck right out
of the sea, so it now sits Locked
section
stranded on an island. It was gives way UNIQUE EARTH
lifted nearly 16 ft (5 m) in less SNAP
than five minutes. Other parts Eventually, the rocks give way. The edge of the
of Alaska sank by 8 ft (2.4 m). upper plate margin springs upwards, pushing the
water up into a giant heap that becomes a tsunami.
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