Download Deep Focus Earthquake

What is an
earthquake?
An earthquake is the
rapid vibration of
the earth created by
a sudden movement
of large sections of
rock
Earthquakes are
caused by tectonic
forces.
When plates move,
stress is put on rocks.
Eventually, these
rocks break, forming
faults.
The “Scientific Explanation”….
•The Earth releases its internal heat by
convecting, (boiling) much like a pot of pudding
on the stove.
•Hot asthenospheric mantle rises to the surface
and spreads laterally, transporting oceans and
continents as on a slow conveyor belt (a.k.a.
“tectonic movement).
•The speed of this motion is a few cms per year
(about as fast as your fingernails grow).
•The pressure from this movement creates a
fault (large crack in the rocks making up the
earth’s crust).
•Rocks moving along these faults create
vibrations, known as earthquakes!
Earthquake Vocabulary
Fault:
a surface between two regions of
rock, along which there has been
rupture and movement in the past
Earthquake
Vocabulary Cont’d
Shear Strength:
The force that is needed to
break a solid material
Elastic Rebound:
The return of a bent elastic solid
to its original shape after the
deforming process is removed
Friction:
The force that resists the
motion of one surface against
another surface
The following diagram illustrates the process of elastic
rebound. Start at the bottom.
-A straight fence is built across the San Andreas fault.
- As the Pacific plate moves northwest, it gradually
distorts the fence.
-Just before an earthquake, the fence has an "S" shape.
-- When the earthquake occurs the distortion is released
and the two parts of the fence are again straight; but
now there is an offset.
This is a
picture of
the offset
fence along
the San
Andreas
Fault after
the 1906 San
Francisco
Earthquake
Offset by 8.5
feet!
Big Quake or Small Quake?
How would you measure the strength of an
earthquake?
The Seismograph
•For centuries different societies have designed many
creative ways to measure the shaking of the earth.
•Nearly 2000 years ago, for example, the ancient
Chinese made a special vase that had several sculpted
dragons mounted all around the sides of the vase.
• Each dragon held in its mouth a metal ball. When the
ground shook, some of the balls would fall from the
mouths of the dragons into the waiting mouths of the
sculpted frogs to show how the ground had moved.
Modern Seismograph
Today’s geologists measure
earthquakes with a seismograph
A typical seismograph works in a
very simple way…
A heavy weight is fastened to a horizontal
rod as shown in the diagram
•This rod hangs from a pole (and is free to
swing from side to side when the ground
shakes.
•At the other end of the rod (away from
the pole) is an ink pen
•directly underneath the pen is a piece of
paper rolled around a cylinder .
This cylinder rotates so that the pen continuously
draws an ink line along the moving paper.
• If the ground does not move, the rod does not
swing, and the pen stays in place, so the ink line is
smooth and straight.
• If the ground shakes, however, the row swings
and so the pen draws a zigzag line as the paper
turns.
• The stronger the shaking, the sharper the
zigzags. This zigzag picture made on the paper
roll is called a seismogram.
Earthquake
Vocabulary Cont’d
• Seismic Waves:
– The shock waves created at the focus of an
earthquake and sent out in all directions
through the earth.
• Seismograph:
– A device that records seismic waves
• Seismogram
– The picture drawn by a seismograph.
3 Types of
Seismic Waves
Types of Seismic Waves:
• Body waves (P and S
waves)
– travel through the
earth’s interior
• Surface waves:
– travel along the
earth’s outer layer
Primary Waves
(P waves):
–Fastest moving (6 km/s)
–First to be recorded by a
seismograph
–Can travel through solids and
liquids
–Effect: Push & Pull--cause rocks
to move back and forth in the
same direction the wave is moving
Secondary Waves
(S waves):
–Second waves to be recorded on a
seismograph (4 km/s)
–Can ONLY travel through solid
material (NOT liquid)
–Effect: Side-to-Side--Cause rocks to
move in right angles to the wave
Both S and P waves travel throughout the body of the earth.
However, it turns out that S waves cannot travel through the
core, and only P waves are recorded in some places
Surface Waves
(a.k.a Long waves; L waves)
–Slowest moving wave
–Last to be recorded on a seismograph
–Move through liquid & solid
–Effect: cause the earth’s surface to
rise and fall
•THESE ARE THE MOST DESTRUCTIVE
WAVES!
Review of waves
Locating & Measuring
Earthquakes
Review of Seismic Waves
• S waves cannot travel through the liquid outer
core.
• They can travel through the mantle because the
mantle behaves more like a solid than a liquid.
– The S waves curve as they move through the mantle
due to refraction as the density of the mantle changes.
• P waves can travel through the whole planet.
– They also curve with the changing density of both the
mantle and the core.
• The P waves change direction at the boundary
between the different layers of the Earth.
– This is due to refraction caused by the different
densities of the layers.
To find the epicenter of an earthquake, scientists
analyze the difference between the arrival times of
• Scientists know the
that:P waves and S wave.
– P waves travel 1.7 times faster
than S waves
Therefore:
If the S waves arrive shortly after
the P waves, then the earthquake must
have occurred nearby

If the S waves arrive a long time after
the P waves, then the earthquake must
be further away
• So……… scientists simply use a graph to
plot the arrival times of the 2 waves.
Then they translate the difference in
times to distance.

Earthquake Measurement:
• Richter Scale- scale that expresses magnitude of
an earthquake
• Magnitude- measure of the energy released by an
earthquake.
•Each whole number increase in
magnitude represents a tenfold
increase in measured amplitude
(height of the wave on
seismograph)
•As an estimate of energy, each
whole number step in the
magnitude scale corresponds to
the release of about 31.7 times
more energy than the amount
associated with the preceding
whole number value.
Mercalli Scale- Scale that expresses the intensity
of an earthquake
Intensity- the amount of damage caused
•Any given earthquake can be
described by only one
magnitude, but many
intensities:
•the earthquake effects
vary with circumstances
such as distance from the
epicenter, quality of
buildings and local soil
conditions.
•Because there is some room
for interpretation in the scale,
the Mercalli scale is not often
used in modern detection of
quakes
Comparing Mercalli Scale w/Richter
Shaking Earth
There are thousands upon thousands of earthquakes annually.
They range, on average, from 18 major quakes to more than 2
million very minor ones per year (approximately 8,000 per
day).
On average, we can expect one exceptionally big one (with a
magnitude of 8 or higher) each year.
Statistics:
The largest earthquake ever
recorded was an 9.5 on the
Richter scale
• Great: 8 or higher
 Major earthquake: 7 -8
• Strong earthquake: 6-7
 Moderate earthquake: 5-6
• Light: 4-5
• Minor: 3-4
• Microquake: lower than 2.5
and is usually not felt by
people
• Location, location, location
Eq Vocabulary Cont’d
Focus:
The location within the earth where underground rock moves and sends out earthquake
waves.
Epicenter:
The location on the surface of the earth directly
above the focus of an earthquake.
The
relationship
between the
focus and the
epicenter of
an
earthquake
Focus Depths
• Shallow Focus Earthquake:
• within 70km of the earth’s
surface
• Intermediate Focus Earthquake:
• between 70km and 300km deep
• Deep Focus Earthquake:
• 300km-650kmdeep
That’s RIGHT!!!!
• Shallow Focus Earthquakes cause the
most amount of damage, because the
strongest vibrations reach the earth’s
surface more quickly
• Deep Focus Earthquakes are the
weakest, because the vibrations lose a
lot of energy as they travel great
distances to the earth’s surface.
• Intermediate Focus Earthquakes are
somewhere in-between!
Secondary Effects of an EQ
• Fires
•
Land Slides
• Tsunamis
• Floods
• Avalanche
Facts & Photos of
Earthquake Damage
Earthquake of
August 18, 1959,
Hebgen Lake,
Montana.
The magnitude 7.1
earthquake killed 28
people and caused $11
million property damage
Great Chilean Earthquake -May 22, 1960
Magnitude 9.5
The earthquake caused a tsunami that hit the Chilean coast
severely, with waves up to 25 meters high, ran through the Pacific
Ocean and devastated Hilo, Hawaii, 10,000 kilometers (6,200
miles) from the epicenter, as well as coastal regions of Japan. The
total number of fatalities from the earthquake/tsunami combination
was estimated to have been as many as 3,000.
Good Friday Earthquake- March 27, 1964
Magnitude 9.2
131 people were killed as a result of the earthquake: nine in the
earthquake itself, 106 from tsunamis in Alaska, and 16 from
tsunamis elsewhere. Property damage was estimated at over
$300 million (1964 dollars), or $1.8 billion 2006 U.S. dollars.
Earthquake of
June 16, 1964,
Niigata, Japan.
The magnitude 7.4
earthquake killed
26 and destroyed
3,018 houses and
moderately or
severely damaged
9,750 in Niigata
Earthquake of
November 23,
1980, Campani,
Italy.
The magnitude 6.8
earthquake killed
over 3,000, injured
7,750, and caused
severe property
damage. An additional
1,575 were reported
missing and presumed
dead. Two hundred
fifty thousand were
reported to be
homeless. Twenty five
thousand square
kilometers of
southern Italy were
devastated.
Earthquake
of February
9, 1971, San
Fernando,
California.
The magnitude 6.7
earthquake killed
66 and caused
$0.5-1.0 billion
property damage.
Loma Prieta earthquake October 17, 1989
7.1 Magnitude
This major earthquake caused 63 deaths, 3,757 injuries, and an
estimated $6 billion in property damage.
August 1999 7.4 Turkey EQ
More than 15,000 people are dead, 23,000 injured, and 500,000
homeless after this earthquake.
Dec. 26, 2004 Indian Ocean Earthquake
Magnitude 8- 9.2*
Its tsunami killed
more than 230,000
people, making it one
of the deadliest
disasters in modern
history.
* the earthquake's magnitude was first
reported as 8.1 by the U.S. Geological
Survey After further analysis, this was
increased to 8.5, 8.9, and 9.0. In February
2005, some scientists revised the estimate of
magnitude to 9.3. The most definitive
estimate so far has put the magnitude at 9.15.
the Pakistani government's official death toll was 87,350
May 12, 2008- Sichuan province China
7. 9 magnitude
69,227 are confirmed
dead, including
68,636 in Sichuan
province, and
374,176 injured, with
18,222 listed as
missing.[6] The
earthquake left about
4.8 million people
homeless,[14] though
the number could be
as high as 11 million.
Haiti Earthquake• 7.0 magnitude
• The Caribbean is not usually
considered a seismic danger zone,
but earthquakes have struck there
in the past.
• Most of Haiti lies on the Gonave
microplate, a sliver of the earth's
crust between the much larger
North American plate to the north
and the Caribbean plate to the
south.
• This is a transform boundary
• Death toll = 150,000 and rising
January 12, 2010
HONSHU, JAPAN- 3/11/11
• One of the 5 most
powerful EQ’s measured
• 15,846 deaths,6,011
injured, and 3,320 people
missing
• Tsunami caused 3 nuclear
reactors to meltdowns at
Fukushima.
• $13-32 billion in damages