Earthquakes
What is an earthquake?
• Earthquake: a sudden release of energy in earth’s
crust that causes movement
Why Earthquakes happen
• Friction prevents movement along a fault
• Fault: a fracture in a rock formation where
movements occurs
• Sudden release causes a quake
Elastic Rebound
• Elastic rebound: the sudden return of deformed
rock to its original position
• Fence offset 8 1/2 feet by
main fault in rural
California1906.
Anatomy of an Earthquake
• Focus: the location within Earth along a fault at
which the first motion of an Earthquake occurs
• The shallower the focus, the more destructive the
quake
Anatomy of an Earthquake
• Epicenter: the location on Earth’s surface directly
above the focus
Seismic Waves
• Seismic Waves: Vibrations caused by
earthquakes
Body Waves
• Body waves: seismic waves that travel through
earth’s interior
• Two types:
• Primary waves: P-waves- Fastest and the first
to be detected
• Can move through solids, liquids, or gas
Body Waves continued
• Secondary waves: S-waves- shake the
ground back and forth (2nd fastest)
• Can move through solids ONLY
Animation
Surface waves
• Surface waves: Only move
along the surface of Earth
• Slower, but cause the most
damage
http://www.tjhsst.edu/~jlafever/wanimate/Wave_Properties2.html
Surface Waves
• Love waves: fastest surface waves
• Move rock side to side
Diagram of love wave
Surface Waves
 Rayleigh waves: also called a “ground roll”
 Moves rock in a circular motion
Seismic Waves and Earth’s Interior
• The composition of the material a seismic wave
moves through affect their speed and direction
• Andrija Mohorovicic (1909): used seismic waves to
find the depth of the mantle
Seismic Waves and Earth’s Interior
• Shadow Zones: locations on Earth’s surface
where no body waves from a particular
earthquake can be detected
animation
Seismic Waves and Earth’s Interior
• P-waves are bent as they
pass through different layers
• S-waves are blocked by the
liquid outer core because
they can only travel through
solids
• Activity 1: Seismic Waves
• Reflection and extension quiz
Studying Earthquakes
• Seismograph: an instrument that detects and
records seismic waves
• Seismogram: the recorded tracing produced by
a seismograph
Studying Earthquakes (cont.)
• Different waves move at different speeds:
• P-waves arrive first, then S-waves, then Surface
waves
Locating an Earthquake
• The longer the lag time between P-waves and S-waves,
the further away the earthquake is
• The location of an earthquake can be found by
triangulation: using the distance from 3 stations to find
the epicenter of the earthquake
http://www.classzone.com/books/
earth_science/terc/content/investi
gations/es1003/es1003page02.cfm
?chapter_no=investigation
Measuring Earthquakes
• Magnitude: the strength of a quake
Measuring Earthquakes
• Richter Scale: assigns a number to define the
energy released during an earthquake
https://www.yo
utube.com/watc
h?v=wVqYg4NP
vC4 richter scale
explained
https://www.y
outube.com/w
atch?v=1qbg7
orb1lc
Bill nye
Measuring Earthquakes
• Big numbers = stronger
earthquakes
Taiwan (1999)
Measuring Earthquakes
• Intensity: the amount of damage caused by an earthquake
Tsunamis
• http://video.nationalgeographic.com/video/101videos/tsunami-101
Tsunamis
• Tsunami: a giant wave caused by an earthquake
on the ocean floor
Earthquake Safety
Earthquake Safety
• Earthquakes are more likely to happen in some places,
but can happen anywhere
• Before: have supplies on hand
• Such as: food, water, flash lights, batteries, radios and a first
aid kit
• During: stand in a doorway, stay away from windows
and tall things
• Protect your head from falling objects
• Drop, Cover and Hold On
• After: be cautious of fires, downed powerlines, etc.
• Remove yourselves from buildings and check for structural damage.
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1005/es1005pag
e01.cfm?chapter_no=visualization
Earthquake Warnings/Forecasts
• Scientists study past quakes to predict where future
quakes are most likely to occur
• There is No reliable way to predict when or where
an earthquake will happen
• When stress is building up in rock, sensors can
detect tilting and cracking
• Foreshocks usually happen before a large
earthquake