Earth
and
quakes
Amole
Spectra
2013
What are
?
• The resulting vibrations that occur from
rocks sliding past one another at a fault
• Caused by pressure experienced at plate
boundaries
• Energy is released as seismic waves
• Seismic waves create the “shaking”
The Ring of Fire
Earthquake Features
• Focus- exact point
inside Earth where
quake originates
• Epicenter- Point on
surface directly
above focus
• Energy travels
outward from these
points in the form of
waves
Types of Seismic Waves
• Primary or P waves– Longitudinal
– From focus
– Fastest (arrives first)
• Secondary or S waves– Transverse wave
– From focus
– Slower (arrives second)
• Surface waves or L
waves– Circular motions
• Up and down
• Back and forth
–
–
–
–
From epicenter
Moves across surface
Slowest (arrives last)
Most destructive
Measuring Earthquakes
• Three Seismograph
• Difference between arrival
times allows seismologists to
calculate the distance to the
epicenter
• Draw three circles with radii
being the distance to
epicenter.
• The overlapping is the
location of the epicenter
Measuring Earthquakes
• The Richter Scale is used to measure the
energy (magnitude) of the earthquake
• Does not predict severity/damage
– Building construction
– Depth of focus
– Soil composition and saturation
– Type of rock
• Mercalli scale rates the quakes effect of
surface (intensity)
Richter Scale
Magnitude
Earthquake Effects
Estimated Number
Each Year
2.5 or less
Usually not felt, but can be
recorded by seismograph.
900,000
2.5 to 5.4
Often felt, but only causes minor
damage.
30,000
5.5 to 6.0
Slight damage to buildings and
other structures.
500
6.1 to 6.9
May cause a lot of damage in very
populated areas.
100
7.0 to 7.9
Major earthquake. Serious
damage.
20
8.0 or greater
Great earthquake. Can totally
destroy communities near the
epicenter.
One every 5 to 10
years
7.8 magnitude (China)
San Francisco, 1906
Alaska Earthquake 1964
Tsunamis are Ocean
Earthquakes
Seismic Waves and Earth’s Interior
• Seismic waves can be used to investigate
the Earth’s interior.
Fact
Observation
Theory
Waves change
Velocity of seismic
The Earth is
speed and
waves are
composed of
direction when the different t different
different layers
density of the
locations
containing
medium changes
different materials
S waves are
S waves do not
Part of the Earth’s
transverse and
reach the side of
core must be
cannot pass
Earth’s core
liquid
through liquids
opposite the focus
http://www.pbs.org/wnet/savageearth/animations/earthquakes/
What is a Volcano?
• An opening in Earth’s crust through which
magma has reached the Earth’s surface
• Release molten rock, ash, and gases
• Often form hills or mountains as lava builds and
cools
• Generally have one central vent
• Magma that reaches the surface is called lava
• Most occur at convergent plate boundaries
The Ring of Fire
Types of Volcanoes
• Shield
• Composite
• Cinder Cones
• Seamounts
• Hot spots
Shield Volcanoes
• Magma rich in iron
and magnesium
• Flows great
distances
• Mild and frequent
eruptions
• Gentle slopes
• Some of the largest
Shield Volcanoes
Mauna Loa, Hawaii
Composite Volcanoes
• Alternating layers of
ash, cinder, and lava
• Magma rich in silica
• Trapped gases cause
eruptions that alternate
between flows and
explosions of cinder
and ash
• Steeper slopes
Composite
Volcanoes
Mt. Vesuvius, Italy
Mt. Rainer, Washington
Cinder Cone Volcanoes
• Smallest and most
abundant
• Violent eruptions due
to large amounts of
trapped gas
• Only active for short
time
• Steepest slopes
Cinder Cone
Paricutin, Mexico
Underwater Volcanoes
• Called seamounts
• Look like composite
volcanoes
• Occur at divergent
plate boundaries
Hot Spots
• Occur in the middle of plates
• Mantle plumes melt as the rise from the
mantle and erupt
• Mantle plumes under oceans create
islands from ash and lava that builds up
and breaks through the surface
• As the plate moves the mantle plume
stays creating a chain of extinct volcanic
islands
The Hawaiian Islands