Download Earthquakes October 15th, 2009

NatGeo Video Clip
http://www.youtube.com/watch?v=CtBXTvtFaCU
What is an Earthquake?
 The movement of tectonic plates creates a great deal of stress
on the earth’s crust
 When the stress becomes too much, part of the crust will
buckle, causing violent motion along a fault line, or fracture
 Most earthquakes occur on the edge of plates, especially when
one plate is forced under another
 Earthquakes vary in their destructiveness which relates to how
close the quake is to the surface
 The point on the earth’s surface immediate above the focus or
where the earthquake originates is known as the epicenter
Earthquake Simulation
 http://environment.nationalgeographic.com/environment
/natural-disasters/forces-of-nature.html?section=t
Tsunamis
 Tsunamis are earthquakes that originate far beneath the
ocean floor and can generate huge waves that can travel
quickly over great distances
 To generate tsunamis, earthquakes must occur
underneath or near the ocean, be large and create
movements in the sea floor
 Can also be caused by landslides and volcanic eruptions
 Tsunami can travel at speeds up to 950 km/h in deep water
which can be represented by the speed of a passenger jet,
and can be 30 m above sea level
How are earthquakes measured?
 Seismologists, the scientist who study earthquakes, are
now able to predict the regions where earthquakes are
most likely to occur
 In 1930, a geologist named Charles Richter developed a
scale for measuring the strength of earthquakes which is
known as the Richter Scale
 The scale is the standard measurement of the force, or
magnitude of the earthquake
The Richter Scale
 Is a logarithmic scale, meaning that the numbers on the
scale measure factors of 10 (an earthquake that measures
3.0 is ten times larger than one that measures 2.0)
 Anything below 2.0 is undetectable to a person and
is called a microquake
 Moderate quakes are rated between 2.0 and 6.0
 Anything above 6.0 can cause severe damage
Where do earthquakes occur?
 Most quakes occur in parts of the world that sit on top of
fault-lines, or boundaries between the major tectonic
plates
 The edges of the huge Pacific Plate, under the Pacific
Ocean, are a particularly active area, which geologists
have nicknamed ‘the ring of fire’
 The ‘ring of fire’ is where it is said that 75% of the Earth’s
active and dormant volcanoes and earthquakes are
located
Seismic Waves and
the Earth’s Core
 How seismic waves travel through the Earth’s core is
dependant upon the material they encounter along the
way
 speeds vary depending on the density and the elastic
properties of the material they pass through, and they are
amplified as they reach the surface
 P waves – Primary wave, is the fastest of the three, able to
move through both liquid and solid rock, compress and
expand material as the move
 S waves – Secondary waves, shear or cut the rock as they
move sideways, CANNOT move through liquid (liquid can
be compressed but not sheared)
 More dangerous than P waves in that they produce
both vertical and horizontal motion