Differentiate focus and epicenter using f

 Earthquake = the shaking and
trembling that results from
movement of rock beneath
Earth’s surface
 Focus = area beneath Earth’s
surface where rock under stress
breaks and causes an
earthquake
 Epicenter = point on the
surface directly above the focus

A. Earthquakes produce vibrations called
Waves.
B. Waves carry energy.
C. Seismic waves are vibrations that travel
through Earth carrying energy released
during an earthquake.

D. Seismic waves carry energy from an
earthquake away from the focus, through
Earth’s interior and across the surface.
E. Three main categories of Waves:
Primary Waves (P waves)
Secondary Waves (S waves)
Surface Waves

 The first waves to arrive are Primary waves.
› P waves compress and expand the ground.
 After P waves come Secondary waves.
› S waves are seismic waves that vibrate from Side to
Side as well as up and down.
 When P waves reach the surface, some of them
become Surface waves.
› Surface waves move more slowly than P or S waves
but they produce severe ground movements.

 There are at least 3 different measures
for rating earthquakes.
 Two methods for measurement:
› Mercalli Scale
› Richter Scale
 Mercalli Scale = Rate earthquakes on the
level of damage at a certain place

 Richter Scale = rating of an
earthquake’s magnitude
based on the size of the
earthquake’s seismic waves
› Magnitude is a number
geologists assign to an
earthquake based on the
earthquake’s size
› the seismic waves are
measured by a seismograph

 Comparing Magnitudes
› An earthquake’s magnitude tells Scientists
how much energy was released by the
earthquake
› Earthquakes with a Magnitude of 6 cause?
 Moderate damage
 32 times the energy of a
Magnitude 5 Quake

 Geologists use seismic waves to locate
an earthquake’s epicenter.

Differentiate focus and epicenter using f

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