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What Makes the Earth Quake?

25 Next time you’re outside, jump up bump and grind together. Finally
and down. Stomp your feet a few the plates break free along a
times. The ground seems solid, section of the fault, releasing
right? Well, not entirely. pent-up energy in an earthquake.

26 The part of the earth you’re The force makes objects move up
standing on, called the and down and in a lateral motion,
lithosphere, is rock-solid. But the and it can cause great destruction.
lithosphere is very thin—if the
earth were the size of an apple,
the lithosphere would be about as
thick as the apple’s skin. If you
dug a hole through the earth,
you’d find that as you went
deeper, what’s inside becomes
hotter and more gooey. The solid
lithosphere is broken up into continental plate
close-fitting plates that drift on
top of the molten rock
underneath. We don’t feel the oceanic plate earthquake epicenter
plates moving because they’re •
usually drifting only a few
centimeters a year—about as fast molten rock
(or slow) as your fingernails grow.

27 Earth’s plates don’t all move
parallel to each other and in the
same direction. At the boundary There are several different types of
where two plates meet, called a faults. The Sunda Fault offshore
fault, they bump and push into from the Batu and Mentawai
each other. They’re wedged islands is called a megathrust,
together most of the time, but where the underwater oceanic
stress builds up as the plates plate dives under the continental
plate.

parallel If two or more things are parallel to each other, they move in the same direction.
lateral If something moves in a lateral way, it moves side to side.
destruction Destruction is the act of destroying or ruining something.

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