Download Earthquake Definitions - Red Hook Central Schools

 Earthquake: the shaking of the Earth’s crust
caused by a release of energy.
 Common cause: movement of the Earth’s plates
 As the Earth’s plates move past one another, friction causes
the plates to get “stuck”.
· Stress and pressure builds up and causes the plate to
become deformed (bend) as it continues to try and move (the
plates are elastic-they can change shape).
· Eventually, the pressure is great enough to overcome the
friction and the plates slip past one another.
· The plate movement is the earthquake. The greater the plate
movement, the larger the earthquake.
· The plates are in a new location, but they go back to their
original shape (rebound).
**Think of pushing on the ends of a wooden ruler. As you
push, the ruler will bend. When you release the pressure on
the ends, the ruler snaps back to its original shape.
 Fault: break in the lithosphere along which
movement has occurred
 Focus: the point at which the first movement
occurs
 Epicenter: the point on Earth’s surface directly
above the focus
 Friction prevents plate movement most of the time.
 Boundary Type vs. Earthquake Depth:
a. divergent boundaries: within 30 kilometers of the
surface
b. transform boundaries: occur at shallow depths
c. subduction boundaries: occur as deep as 700 km
 Body wave: travels from the focus of an
earthquake through Earth
 P-wave: a body wave that squeezes and
stretches rock materials
- also known as a compression wave or a primary
wave
- P-waves can travel through any material- solid,
liquid or gas
 S-wave: a body wave that causes
particles of rock to move at right
angles
-also known as shear waves or as
secondary waves
-can travel through only solids, not
liquid or gas
 P and S waves
 Surface wave: a wave that travels
along Earth’s surface- caused by
body waves
 Surface waves cause
considerable damage
 The rate at which P waves and S waves travel
depends on the type and density of the material
through which they travel
 The waves move faster when material is rigid
and dense
 S waves travel at a little less than half the speed
of P waves
 Surface waves travel the slowest when
compared to P and S waves