Defined

Two blocks of the earth’s crust slip past each
other after having been stuck together
 The two pieces are trying to move past one
another but the pieces stick together because of
friction.
 The energy trying to push the pieces gets stored.
 When the pieces finally move (overcome friciton),
the stored energy gets released all at once.

The energy moves the pieces of crust. This
movement is the earthquake.
A picture of it…

Tokyo 2011
Parts of an Earthquake
Focus—the origin of the
earthquake; the point of
slippage
 Epicenter—the point on
the surface directly above
the focus
 Fault—the plane along
which the slipping
happens
 Focal depth—how deep
the earthquake occurs

The Energy Released
Is in the form of waves.
 Radiates outward in all directions from a
central point like ripples in a pond

 the energy travels through the Earth and
along the surface of the earth after an
earthquake

These waves cause the earth
movements that you feel during an
earthquake
Types of Seismic Waves

Body waves
 P-waves—primary waves
 S-waves—secondary waves

Surface waves
 L-waves—love waves
 Rayleigh waves
General Comparisons

Body waves travel through the earth
 How scientists “know” the outer core of the
earth is liquid. S-waves don’t pass through.
 Seismographs around the world register
earthquakes from all over the world.

Surface waves travel only the earth’s
surface
 Lessen in intensity the farther away from the
epicenter you get
Shadow Zone

P-waves travel
through solid and
liquid
 BUT they bend
when the hit liquids
(refraction—like a
pencil appears bent
in water)

S-waves only
travel through
solids
A comparison—p waves
P-waves travel the fastest.
 Do the least damage
 Can travel through solids and liquids
 Pushes and pulls the particles
 P-wave animation

A comparison—s waves
Slower than p-waves
 Little damage done
 Move particles perpendicular to direction
of wave propagation
 S-wave animation

A comparison—L waves
Slower than s-waves
 Responsible for most of the damage
 Moves the ground from side to side
(produce all horizontal motion)
 L-waves animation

A comparison—Rayleigh waves
Slowest moving wave
 Responsible for most of the damage
(with love waves)
 Waves roll the ground up-and-down and
side-to-side
 Responsible for most of the shaking
 Rayleigh wave animation

How Big was it?
Depends on the size of the fault and the
amount of slippage
 Magnitude is size of the earthquake.

 Measured on the Richter scale
 Tells “how much slippage” occurred

Sometimes described with intensity as
well
 Measured on the Modified Mercalli scale
Richter Scale


Measures the
amplitude of the
wave shaking
the earth
Logarithmic
scale
 Each number
increase = 10
times bigger
amplitude of
shaking and 32
times more
energy released
Eureka CA
9 jan 2010
6.5 magnitude
http://www.latimes.com/news/local/la-me-eurekaquake-pictures,0,7163381.photogallery
http://www.latimes.com/news/local/la-me-eurekaquake-pictures,0,7163381.photogallery
Port-a-Prince, Haiti
12 january 2010
7.0 magnitude
3 times stronger than Eureka
http://www.boston.com/bigpicture/2010/01/earthquake_in_haiti.html
Why so much more damage?
http://www.boston.com/bigpicture/2010/01/earthquake_in_haiti.html
Sichuan Province, China
Magnitude 8.0 May 2008
http://media.theaustralian.com.au/multimedia/2008/05/13-quake/index.html
http://media.theaustralian.com.au/multimedia/2008/05/13-quake/index.html
Japan, 3 mar 2011,
magnitude 8.9

Japan Earthquake
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html
A seismograph
Shows the amount the
surface of the earth
moves on a
seismograph
 Due to inertia the
weight doesn’t move.
The paper moves
under the weight.
 The bigger the
squiggle, the bigger
the quake

http://earthquake.usgs.gov/learn/kids/eqscience.php
Modified Mercalli Scale
Measures the
effect of the
earthquake on an
area
 Subjective—no
mathematical
basis
 Arbitrary rating
based on
observations

Associated Hazards
Landslides
 Liquefaction
 Volcanic Eruptions
 Tsumanis

Liquefaction
Saturated soil becomes unstable due to
the shaking of the earth.
 Loses its strength and stability
 More likely in sand soils
 Liquefaction

Japan—11 mar 2011
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html
Japan
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html
http://www.boston.com/bigpicture/2011/03/massive_earthquake_hits_japan.html

Tsunami Formation
Finding the Epicenter



Measure the S-P times on
seismograms for 3 different
locations and record the times
Determine the distance for each S-P
time from the travel time curves
Triangulate using circles—the
epicenter is where the 3 intersect.
Time Travel Curve
Triangulation
Any questions?