Transcript Earthquakes!!!!!

EARTHQUAKES!!!!!
An earthquake is the vibration
of the Earth that results in a
sudden release of energy in
the Earth’s crust that creates
seismic waves.

Earthquakes are also
known as quakes,
tremblors or tremors.

At the Earth's surface,
earthquakes manifest
themselves by shaking and
sometimes displacing the
ground.

The point deep within the crust
where plate contact is made is
called the focus. The point on
the Earth’s surface (directly
above the focus) is called the
epicenter.

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A fault is a fracture in rock in which the
rock on one side of the fracture has
moved with respect has moved with
respect to the rock on the other side.
Earthquakes are caused by the energy
release during rapid slippage along a
fault.
La faille des Causses, une faille des
Grands Causses, vue depuis Bédarieux
(Hérault, France)
Slippage Along a Fault
What happens to the plate during
an earthquake?
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When plate boundaries move (either
transform fault, convergent, or
divergent), they will move freely and
easily if the two plates are smooth.
But plate boundaries are not smooth
and the edge of the plate can get
“caught.”
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When the edges get “caught,” great
pressure gets exerted on the plate. This
pressure translates into potential energy.
When the energy becomes too great and
the strength of the rock is exceeded, the
plate slips or cracks and a rapid release
of potential energy (stored in rock)
occurs.

Earthquakes are recorded with a
seismograph using one of two
scales called the Moment
Magnitude or the Richter scale
(mostly obsolete among
seismologists).
Seismograph and Seismograms
 Seismograms are traces of
amplified, electronically recorded
ground motion made by
seismographs.
 A seismogram shows all three types
of seismic waves—surface waves, P
waves, and S waves.

Most mechanical seismographs
have been replaced by digital
recorders that store the
seismogram electronically.
Seismograph Stations in California
Wave Energy

The energy found in an
earthquake is wave energy.

There are two types of waves:
surface waves and body waves.
Surface Waves

Surface waves are seismic waves
that travel along Earth’s surface
(many P and S waves turn into
surface waves when they reach the
surface).

These are the rolling waves you feel
during an earthquake.
Body Waves
The two types of body
waves are: P waves and
S waves.

P(primary) waves!
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P waves are push-pull waves that
push (compress) and pull (expand) in
the direction that the waves travel;

P waves travel through solids, liquids,
and gases;

P waves have the greatest velocity of
all earthquake waves.
S (secondary) waves!
S waves are seismic waves that
travel through the Earth;
 S waves shake particles at right
angles to the direction that they
travel;
 S waves travel only through solids;
 S waves have slower velocity than P
waves

Seismogram
Moment Magnitude and Richter Scale
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The moment magnitude scale is used
by seismologists to measure the size
of earthquakes in terms of the
energy released.
This scale was developed in the 70’s
and is used by seismologist as
opposed to the 30’s era Richter scale.

The moment magnitude scale is based
on the moment of the earthquake,
which is equal to the rigidity of the
Earth multiplied by the average
amount of slip on the fault and the
size of the area that slipped.

Both the Moment Magnitude and the
Richter scales are based on multiples
of ten. They are logarithmic scales. So
each whole number (greater or less)
is ten times (more or less) than the
next.

SO…. How much stronger is a 5.0
earthquake than a 4.0?
 10
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times
How much weaker is a 4.5 than an 8.5?
 10,000
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times
How much stronger is an 8.8 (Chile) than
a 6.5 (Northridge)?
 About
100 times.
Richter Scale
Richter magnitudes
Less than 2.0
Description
Micro
2.0-2.9
Earthquake effects
Microearthquakes, not felt.
Frequency of occurrence
About 8,000 per day
Generally not felt, but recorded.
About 1,000 per day
Often felt, but rarely causes damage.
49,000 per year (est.)
Minor
3.0-3.9
4.0-4.9
Light
Noticeable shaking of indoor items, rattling noises. Significant
6,200 per year (est.)
damage unlikely.
5.0-5.9
Moderate
Can cause major damage to poorly constructed buildings
over small regions. At most slight damage to well-designed
buildings.
800 per year
6.0-6.9
Strong
Can be destructive in areas up to about 160 kilometres
(100 mi) across in populated areas.
120 per year
7.0-7.9
Major
Can cause serious damage over larger areas.
18 per year
Can cause serious damage in areas several hundred miles
across.
1 per year
8.0-8.9
Great
9.0-9.9
10.0+
Epic
Devastating in areas several thousand miles across.
Never recorded; see below for equivalent seismic energy
yield.
1 per 20 years
Extremely rare (Unknown)
Results of Earthquakes
Tsunami (from underwater earthquakes)
 Landslides
 Volcanoes (like Mt. St. Helens)
 Urban Fires
 Floods
 Fissures
 Avalanches
 Loss of human life and property
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Causes of Earthquakes
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Earthquakes are caused mostly by
rupture of geological faults, but also by
volcanic activity, landslides, mine blasts,
dams (waterquakes), and nuclear
experiments.
Remember: Faults are fractures in Earth
where movement has occurred.

An aftershock is a small
earthquake that follows the main
earthquake.

A foreshock is a small
earthquake that often precedes a
major earthquake.
Largest Earthquakes in the World!
Rank
1
2
3
4
4
4
5
5
5
6
6
6
7
7
7
Date
May 22, 1960
December 26, 2004
March 27, 1964
November 4, 1952
August 13, 1868
January 26, 1700
November 25, 1833
February 27, 2010
January 31, 1906
February 4, 1965
November 1, 1755
July 8, 1730
March 28, 2005
March 9, 1957
August 15, 1950
Location
Valdivia, Chile
Sumatra, Indonesia
Prince William Sound, AK
Kamchatka
Arica, Chile
Cascadia subduction, Canada/USA
Sumatra, Indonesia
Maule, Chile
Ecuador/Colombia
Rat Islands, Alaska
Lisbon, Portugal
Valparaiso, Chile
Sumatra, Indonesia
Andreanof Islands, Alaska
Assam, India /Tibet, China
Magnitude
9.5
9.3
9.2
9.0
9.0
9.0
8.8
8.8
8.8
8.7
8.7
8.7
8.6
8.6
8.6
Deadliest Earthquakes in the World
Rank
Date
Location
Fatalities Magnitude
1
January 23, 1556 China
830,000
8.0
2
July 28, 1976
China
255,000
7.5
Estimated death toll as high as 655,000
3
January 12, 2010 Haiti
240,000
7.0
4
December 16, 1920 China
234,117
7.8
5
December 26, 2004 Indonesia
230,210
9.3
Deaths from earthquake and resulting tsunami.
6
October 11, 1138 Syria
230,000
8.5
7
September 1, 1923 Japan
142,000
7.9
8
October 6, 1948
Turkmenistan 110,000
7.3
Long Valley (SUPERVOLCANO!)
Earthquakes!
Los Angeles
Earthquakes!
Depth of the Recent Earthquakes
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Chile’s earthquake’s depth was
21.7 miles.
Haiti’s earthquake depth was 8.1
miles.