Transcript What are Earthquakesx

What are Earthquakes?
Earthquakes
• Sudden release of energy in the crust
– Tremors – small shaking of the crust
Today’s earthquakes
– About 2 Earthquakes occur every second.
– But most are too small to be felt.
– Most Earthquakes occur near plate boundaries
– Deepest earthquakes occur on subduction zones
(convergent boundaries)
Where Does an Earthquake Start?
EPICENTER –
POINT
DIRECTLY
ABOVE THE
FOCUS ON
THE SURFACE
FOCUS – STARTING POINT OF AN
EARTHQUAKE BELOW THE SURFACE
Damage Caused by Earthquakes
• Faults
• **** Most death’s and injuries are caused by falling buildings
(Earthquakes don’t kill people buildings kill people).
• Broken gas lines can lead to fires.
• Broken water pipes compound the problem. because there is less
available to put out the fires.
• Landslides and mudflows
• Liquefaction of soil (soil becomes so unstable that it moves like a
fluid)
• Tsunamis – extreme ocean waves caused by earthquakes
• Tsunami detection system
Damage is Amplified
• Create Your Own Earthquake and Building
Structures: compare damage
• Damage will be more severe when building on
loose sediments
• The loose sediments will move more and
result in liquefaction (soil acting as a fluid)
– Houses could sink into the loose sediments
Damage Prevention
• Build on strong solid bedrock
• Build Earthquake proof buildings – buildings
that have internal gyroscopes which allows
the building to move with the lithosphere.
• Securely mount art to walls.
• Avoid windows and move under a table to
prevent being hit by falling objects
Earthquake Preparedness
•
•
•
•
Follow damage prevention plan
Have a short food and water supply
Evacuation Plan
Move to higher ground to avoid Tsunami
Measuring Seismic Waves
• Seismograph – machine
that measures seismic
waves at a given
location
• Seismogram – record
sheets of waves created
by the seismograph
Scales used to Report Earthquakes
• Mercalli
• Measures strength of an
Earthquake according to the
amount of damage done
• Measures Intensity (by how
intensely it was felt)
• Scale ranging between I-XII
• Not always accurate b/c some
locations may incur severe dmg
even when the EQ was not that
strong (If buildings and structures
are built on loose sediments then
eqs are amplified
• Intensity measurements of the
1906 San Francisco Earthquake
• Richter
• Measures MAGNITUDE of EQ
based on Seismic waves
Mercalli Scales
Scales used to Measure E.Q’s
•
•
•
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002pag
e01.cfm?chapter_no=visualization
** p & s waves animations
•
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1009/es1009pag
e01.cfm
Shadow zone
•
•
http://www.thetech.org/exhibits_events/online/quakes/waves/p&s_waves.html
Wave slinky and rope animation
•
•
http://www.wwnorton.com/college/geo/egeo/flash/8_2.swf
P and s waves
http://www3.interscience.wiley.com:8100/legacy/college/skinner/0471152285/anim
ations/animations/mod_5/seismic_waves.html
Wave animations and shadow zone
http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Shadow+Zone+
Flash+Animation&flash_file=shadowzone&flash_width=220&flash_height=300
Shadow zone