Download What is an earthquake?

What is an earthquake?
• Used to describe both sudden slip on a fault,
and the resulting ground shaking and radiated
seismic energy caused by the slip
• Caused by volcanic or magmatic activity,
• Caused by other sudden stress changes in the
earth.
What causes earthquakes?
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
– Plastic deformation – does not cause earthquakes
– Elastic deformation – rock stretches then reaches
a breaking point, releasing energy.
What causes earthquakes?
• As soon as the rock breaks, there is movement
along the broken surface causing a split in the
surface called a fault.
• The seismic waves from an earthquake are
usually strongest at the epicenter, the point on
the surface right above the focus.
Focus –
point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus
Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Seismic waves
• Seismic waves are recorded and measured by
an instrument called a seismograph.
• Seismic waves inside Earth are called body
waves.
• The two main types of body waves are Pwaves and S-waves.
Seismic Waves
• Seismic waves radiate
from the focus after the
earthquake.
• Three seismic stations can
accurately determine the
times of body wave
arrival.
• The larger the difference
in arrival time, the farther
the epicenter is from the
station.
Primary Waves (P Waves)
• A type of seismic wave that compresses
and expands the ground
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Comparing Seismic Waves
• http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1002/es1002
page01.cfm?chapter_no=visualization
Damage: Causes
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Ground motion
Duration of Shaking
Surface Rupture
Poor building design
Effects
• Rupture
• Death
• Bldg collapse
Effects
• Fires
• Liquifaction
• Landslides
Damage: Key
Factors
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Amount & duration of shaking
Water content of soil
Population concentration
Building construction
Distance from Epicenter
Depth of focus
Direction of rupture
Material amplification
Addressing the
Hazard
• Identify areas at risk
• Forecast
Addressing the
Hazard
• Structural adaptations
• Warning systems
Earthquake Waves & Earth’s Interior
Seismic
Waves in
the Earth
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Surface Waves
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive
How do scientists calculate how far a location is
from the epicenter of an earthquake?
• Scientists calculate the difference
between arrival times of the P waves
and S waves
• The further away an earthquake is, the
greater the time between the arrival of
the P waves and the S waves
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Measurement
• Magnitude
– one per earthquake
– related to energy released
– Richter or Moment scale
• Intensity
– many for each
earthquake
– measure of effects
– Mercalli scale
How are Earthquakes Measured?
Richter Scale
Measuring Earthquakes
The Richter scale ranks earthquakes
according to their magnitude of the
seismic waves recorded on a seismograph.
How are Earthquakes Measured?
Mercalli Intensity Scale
Click Link for Interactive Demo
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
Measuring earthquake damage
• The Modified
Mercalli scale has 12
descriptive
categories.
• Each category is a
rating of the damage
experienced by
buildings, the
ground, and people.
Earthquakes and Plate boundaries
• Earthquakes
commonly occur
at the boundaries
of lithospheric
plates.
• This is because
plate boundaries
tend to be zones
of seismic activity.
Tsunamis
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt