Download Earthquakes



An earthquake is ground movements that
occur when blocks of rock in Earth move
suddenly and release energy.
Earthquakes occur along fault lines.
◦ Faults are breaks in Earth’s crust where blocks of
rock slide past each other.

As the plates move, pressure builds up near
their edges, causing fault lines.


The Focus is the place beneath Earth along a
fault line where a block of rock breaks
causing an earthquake.
The Epicenter is the exact spot on Earth’s
surface directly above the focus.


A wave is a disturbance in an substance that
transports energy from one place to another.
Seismic waves are vibrations given off by
Earthquakes that cause ground movements.
◦ When blocks of rock break, the released energy
travels in seismic waves.

Body waves (travel through Earth)
◦ P waves (primary waves) travel through solid, liquid,
and gas because they move in a back and forth
direction (slinky).
 fastest
◦ S waves (secondary waves) can only travel through
solids because they move up and down.
 Second Fastest

Surfaces Waves
◦ Only travel along Earth’s Surface.
◦ Travel back and forth and up and down.
◦ Slowest.


A seismograph is a tool used to measure the
size of an Earthquake based on seismic
waves.
The Richter Scale measures the ground
motion of Earthquakes.
◦ A scale of 1-10 where each magnitude increase is
equal to 10 times the ground movement.

The moment magnitude scale
◦ The modern rating system which measures the
energy output of an earthquake.

Mercalli Scale
◦ Measures earthquakes by the amount of damage
they produce. (intensity)

Stress is pressure on a block of rock causing
it to bend and break (caused by Earth’s
plates).

Tension stress stretches rock, making it
thinner. (occurs at Divergent Boundaries)

Compression stress shortens and squeezes
rock. (occurs at Convergent Boundaries)

Shear stress pushes different blocks of rock
past each other. (Occurs at Transform
Boundaries)
◦
Faults are breaks in Earth’s crust where blocks of
rock slide past each other.

Normal fault
◦ Caused by tension and can be found at divergent
boundaries.

Reverse Fault
 Are a result of compression and can occur at
convergent plate boundaries.

Strike Slip Fault
 Caused by shearing and can be found at transform
boundaries.

The Law of Superposition
◦ If rock layers are undisturbed, the youngest will be
on top. Rocks will get older the deeper you get into
the crust.
◦ Sediments are continuously deposited on top of
each other.
◦ If rock layers are undisturbed, the deeper you get
the older the rocks, fossils, etc. are.

When rock layers are disturbed or changed,
the oldest is not always found on the bottom.
◦ Folding, faulting, and the rise of magma change
rock layers.
◦ Anytime igneous rocks cut across sedimentary rock
layers, they are the youngest.
◦ This causes the law of superposition to be incorrect
at times.

The movement of Earth’s Plates and
convection currents causes the rock cycle.
◦ Zones of subduction form magma, which rises and
creates igneous rocks.
◦ Zones of subduction also create metamorphic rock,
exposing rocks to extreme heat and pressure.
◦ When mountains are formed, they will weather,
creating sediments and sedimentary rock.