Earthquakes and
Seismic Waves
Chapter 2 Section 1
Objectives
 F.2.2.1. Describe how the energy of an
earthquake travels through Earth.
 F.2.2.2. Identify the scales that are used to
measure the strength of an earthquake.
 F.2.2.3. Explain how seismologists find the
epicenter of an earthquake.
 Start Epicenter Lab
What is an earthquake?
 An earthquake is the shaking of the ground
that results from the movement of rock in the
ground.
 Does anyone remember what I told you
earlier causes earthquakes?
 It’s the rebound, or the rock returning to it’s
original shape after deformation.
Elastic Rebound
Earthquake Focus
The focus is
the spot
beneath the
ground where
the
disturbance
originates.
Earthquake Epicenter
The
epicenter is
the spot on
the surface of
the ground
directly
above the
focus.
Types of Seismic Waves
 What are the three types of
seismic waves?
 Primary Waves
 Secondary Waves
 Surface Waves
Primary Waves
Primary waves
move the
particles back
and forth
parallel to the
direction of the
wave.
Secondary Waves
Secondary
waves move
the particle up
and down
perpendicular
to the direction
of the wave.
Surface Waves
Surface
waves
combine
both vectors
and produce
a rolling
motion.
Primary Wave
Secondary Wave
Surface Wave
Surface Wave
How To Reduce The
Effect Of Ground Shaking
Wave In RR Tracks
Measuring Earthquakes
 The three common scales used to measure
an earthquake are:
 Mercalli Scale
 Richter Scale
 Moment Magnitude Scale
Earthquake Scales
Mercalli Scale
Looks at the
damage
caused.
See Figure 9 on
page 55 in your
book.
Richter Scale
Looks at the
size of the
seismic waves
on the
seismograph.
Seismograph &
Seismogram
Seismograph
Seismogram
How A Seismograph
Works
Comparing Magnitudes
 The intensity of an
earthquake increases about
32x’s for each step. A 5 is
32x’s more intense than a 4
and a 6 is about how much
stronger. Think 32 x 32=
 1000 times stronger
Locating an Epicenter
 Why do we need three locations
to find the epicenter of an
earthquake?
 To pinpoint the location through
triangulation.
Locating the Epicenter
Locating the Epicenter
U.S. Earthquake Risk
Map
Begin Epicenter Lab
See pages 57-59 in your
textbook for more detailed
procedures.