Earthquakes

EARTHQUAKES

Prepared by

Abdelrahman Ismail Hassan

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Introduction to Earthquakes: (1.1-1.4)
(1-1) : History of Earthquakes.
(1-2) :What is the Earthquakes.
(1-3): What is the Seismic Waves and it’s types.
(1-4) :Epicenter location
Earthquake Causes (2.0)
Earthquake classification Scale (3.1-3.2)
(3-1) Predictions
(3-2) Scales ,Measuring, and forecasting (Richter & Mercalli scale)
Earthquake Locations (4.1-4.3)
(4-1) Locations
(4-2) 10 Most Destructive Earthquakes
(4-3) Earthquakes in Egypt
Types of earthquakes.(5.0)
Effects of Earthquakes.(6.1-6.2)
(6-1) Effects of Earthquakes
(6-2) The Great Sumatra-Andaman Earthquake/Tsunami
Conclusion .

(1-1) History of Earthquakes.
• Earthquakes have been recorded as early as 1177 B.C.
in China. Of course earthquakes have been a part of
myth and legend since the dawn of man.
• In
Greek
Mythology, Poseidon
was "God of the
Sea". Yet one of his
powers was thought
to be the reason of
Earthquakes.
Introduction to Earthquakes

• Aristotle was one of the first Europeans to create
a theory about the origin of Earthquakes. He
thought that they were the result of heavy winds

• Not much more study
was concentrated on
earthquakes until the
mid-1700s.


• Soon scientists from several countries were exchanging
observations and theories on earthquakes.

• In the 1850s Robert Mallet, figured out a means to
measure the velocity of seismic waves. Meanwhile, in
Italy, Luigi Palmieri invented an electromagnetic
seismograph that was the first seismic instruments
capable of detecting earthquakes imperceptible to
human beings.


• It was about 1910 that Alfred Wegener published his
theory of plate tectonics to explain volcanic and seismic
activity.
• Since then, seismologists have continued to work at a
furious pace, building better instruments, computer
models, theories and forecast to study the causes and
effects of earthquakes.


(1.2)What is the Earthquake :
• What is the Earthquake ?
• It is the vibration of the ground due to the sudden
release of energy by the breaking and shifting of rock
beneath the Earth´s surface and it creates seismic
waves.
• The Earths crust near tectonic plate edges are forced
to bend, compress, and stretch due to the internal
forces within the earth, causing earthquakes.


• (1-3)What is the Seismic Waves:
Seismic waves are generated by the release of energy
during an earthquake. They travel through the earth like
waves travel through water.
• Focus (Hypocenter): spot
underground where the
rock begins to break.
• Most foci are located within
65 km of the Earths
surface, however, some
have been recorded at
depths of 700 km.

• Epicenter: The location on the Earths surface
directly above the focus.

• Aftershock: tremors that occur as rocks adjust to
their new position.



Two types of seismic waves are generated at the
earthquake focus:

1.

Body waves: spread outward from the focus in all

directions.
2.

Surface waves spread outward from the epicenter

to the Earth’s surface
These waves can move rock particles in a rolling
motion that very few structures can withstand.
These waves move slower than body waves


Body waves:
1. Primary Wave (P wave):
• Compressional wave (travels in the same direction
the waves move
• Very fast (4-7 km/second)
• Can pass through a fluid (gas or liquid)
• Arrives at recording station first


• 2. Secondary Wave (S wave):
• Transverse wave (travels perpendicular to the wave
movement
• Slower moving (2-5 km/second)
• Caused by a shearing motion
• Cannot pass through a fluid (gas or liquid)


• Surface waves:

are produced when earthquake
energy reaches the Earth's surface. Surface waves
moves rock particles in a rolling and swaying
motion, so that the earth moves in different
directions. These are the slowest moving waves, but
are the most destructive for structures on earth.
1. Love (L) wave: Rock moves from side to side like
snake
2. Raleigh wave: Rolling
pattern like ocean
wave

(1-4)Epicenter location:

• Earthquake scientists, or seismologists, can locate
the epicenter of an earthquake as long as the
vibrations are felt at three different seismograph
stations by:
1. Locate at least 3 stations on a map that recorded
the seismic waves
2. Calculate the time difference between arrival of Pwaves and arrival of S-waves from a seismogram
3. The epicenter is where the circles intersect.


Epicenter location using three stations

McGraw Hill/ Glencoe, 1st ed., pg 170


• How Earthquakes Happen?

• Most earthquakes are caused indirectly by plate tectonics.
• Plates move at 1-10 cm/year (about how fast your fingernails
grow) and have moved vast distances in the Earth’s 4.6 billion
year history.
Earthquake Causes

Earthquake locations around the world and their correlation to plate boundaries.
Plate boundaries are outlined by red circles, which indicate past earthquake epicenters.

Earthquakes Causes

• There are approximately 7 major and 12 minor plates.
The boundaries between plates often do not coincide
with the boundaries between continents and oceans.
• There are three types of boundaries between plates:
• (1) convergent [plates coming together]
• (2) divergent [plates separating]
• (3) transform [plates sliding past one-another].
FEMA 159. Earthquakes. Produced by The National Science Teachers Association, 1992.

Earthquake Causes

• Faults
Plate movement or other forces can cause tremendous
stress on the rocks that make up the earth’s outer shell.
When rock is strained beyond its limit, it will fracture, and
the rock mass on either side will move. This fracture is
called a fault. Faults often are classified according to
whether the direction of movement is predominantly
horizontal or vertical

FEMA 159. Earthquakes. Produced by The National Science Teachers Association, 1992.

• Intraplate Activity :
Plate tectonics involves inter-plate, or “between-plate,”
activity. Although this theory explains plate boundary
earthquakes, it does not explain all seismic activity. Many
large,
devastating
earthquakes
occur
within
continents, away from plate edges. These earthquakes
are caused by intra-plate activity. The 1811 and 1812
New Madrid fault earthquakes in the central United
States are a good example of earthquakes caused by
intra-plate activity.
Earthquakes of this type probably result from more
localized geological forces such as mid-plate compression

• Sudden Rupture
• during an earthquake when a sudden rupture occurs
along a fault. As the rupture travels through the
rock, energy is released that creates the motions
associated with an earthquake.
• If a fault rupture is shallow enough, the fault line may
appear on the earth’s surface.
• Most rocks are brittle above 15-20 km depth and
ductile below this depth. This boundary is called the
brittle-ductile transition (BDT), and corresponds to a
temperature of 300-450ºC.

• Most deep earthquakes (greater than BDT depth) occur
at subduction zones in a zone called a Wadati-Benioff
zone which extends to 670 km depth.
• Deep earthquakes occur in the Wadati-Benioff zone for
two reasons:
1. rocks remain cool, below the BDT temperature
2. sudden mineral changes induce zones of weakness that
allow rocks to suddenly shift, producing earthquakes.

Earthquake classification scales (Forecasting &Measuring)

(3.1) Predictions
• Earthquakes can be felt over large areas although they
usually last less than one minute.
• Earthquakes cannot be predicted -- although scientists are
working on it
• It is thought that some animals may feel vibrations from a
quake before humans, and that even minutes before a quake
dogs may howl and birds fly erratically.
• Most of the time, you will notice an earthquake by the
gentle shaking of the ground. You may notice hanging plants
swaying or objects wobbling on shelves.
Earthquake classification scales

• Earthquakes can be very destructive at the Earths
surface. The magnitude of an earthquake is a measure
of how destructive it is. Basically the magnitude
corresponds to how much energy is released.
• Today, a standard magnitude scale is used, Seismic
Moment, which more accurately represents the energy
released in an earthquake, especially large magnitude
events.

• Thousands of earthquakes are recorded every day with
magnitudes < 3.0 but are almost never felt.

(3.2) Scales (Forecasting &Measuring)
 Seismometer: instruments that detect seismic waves
 seismogram is visual record of arrival time and magnitude of
shaking associated with seismic wave

 Seismograph: device that measures the magnitude of
earthquake


 Mercalli Intensity scale:
measures the intensity of how people and structures are
affected by the seismic event. In essence, it measures
damage. It is much more subjective and uses numbers
ranging from 1 (no damage) to 12 (total destruction).


 Richter Scale- (logarithmic scale)
• The Richter Scale is used to express
earthquake magnitude on the basis of the
height (amplitude) of the largest line (seismic
wave, P or S) on a seismogram.
• The Richter scale was originally developed for
earthquakes in Southern California. The utility
of this scale was its ability to account for
decreased wave amplitude with increased
distance from the epicenter.


Complications of the Richter scale include:
1. The Richter scale originally only applied to shallow-focus
earthquakes in southern California so now must be modified.
2. Magnitudes calculated from seismograms above 7 tend to be
inaccurate.

MERCALLI VS. RICHTER


Earthquake Locations
(4-1) Locations
• No part of the Earth's surface is safe from
earthquakes. But some areas experience them more
frequently than.
• Earthquakes are most common at plate boundaries,
where different tectonic plates meet. The largest
events usually happen where two plates are
colliding - this is where large amounts of stress can
build up rapidly.
•


Plate boundaries


• About 80 percent of all recorded earthquakes occur
at the circum-Pacific seismic belt (also known as
The Ring of Fire).

The Ring of Fire

• Intraplate earthquakes occur less commonly. They
take place in the relatively stable interior of
continents, away from plate boundaries. This type of
earthquake generally originates at more shallow
levels.

2

1

Intraplate earthquakes


3

Earthquakes map world (USGS 2004-2010)

(4-2) 10 Most Destructive Earthquakes


• (4-3) Earthquakes in Egypt :
• The 1992 Cairo earthquake occurred on 12
October, near Dahshur, 35 km south of Cairo. The
earthquake had a magnitude of 5.8, but was unusually
destructive for its size. The earthquake was felt
throughout most of northern Egypt, in Alexandria, Port
Said and as far south as Asyut, and in southern Israel.
• The Earthquake caused about 545
deaths, injuring 6,512 and making
50,000 people homeless. It was the
most damaging seismic event to
affect Cairo.

•

Many buildings and monuments were severely
damaged or collapsed. Modern concrete skeletal
structures suffered minor nonstructural damage.

• Earthquake physical damage was estimated at
about one billion U.S. Dollars.

• The 1995 Gulf of Aqaba earthquake (Nuweiba
earthquake) occurred on November 22 and registered
7.3 on the moment magnitude scale.
• The epicenter was located 60 kilometers south of the
head of the Gulf of Aqaba where the countries of
Egypt, Israel, Jordan, and Saudi Arabia converge.


• At least 8 people were killed and 30 were injured in
the meizoseismal area.
• Damage to buildings occurred in the coastal cities
of Eastern Egypt.


(5.0)Types of earthquakes:
There are three different types of earthquakes:
tectonic, volcanic, and explosion. The type of
earthquake depends on the region where it occurs and
the geological make-up of that region.

1. Tectonic earthquakes:
These occur when rocks
in the Earth's crust break
due to geological forces
created by movement of
tectonic plates.
Types of earthquakes

2. Volcanic earthquakes: occur in conjunction
with volcanic activity.


3. Explosion earthquakes result from the
explosion of nuclear and chemical devices.


(6-1) Effects of Earthquakes
1. Ground Displacement
Ground surface may shift during an earthquake (esp. if
focus is shallow). Vertical displacements of surface
produce fault scarps Landslides.
2. Liquefaction and Landslides:
Results in a loss of soil strength & the ability of the soil to
support weight

Effects of earthquakes

3. Fatalities(Death)


4. Fires: Fires often break out following earthquakes.
Fires can easily get out of control since the
earthquake. There are many demands made on the
emergency response systems that slow down
response to fires.


5. Shaking and Collapse of Building :
Frequency of shaking differs for different seismic waves.
High frequency body waves shake low buildings more.
Low frequency surface waves shake high buildings more.
Intensity of shaking also depends on type of subsurface
material.


6. Seiches
• The back & forth movement of water in a semi closed/closed body of
water- could cause flooding more from submarine landslide.
• In 1959, a 7.3 magnitude earthquake occurred in Montana. As a
result of faulting near Hebgen Lake, the bedrock beneath the lake
was permanently warped, causing the lake floor to drop and
generate a seiche. Maximum subsidence was 6.7 meters in Hebgen
Lake Basin. About 130 square kilometer subsided more than 3
meters, and about 500 square kilometers subsided more than 0.3
meters.


7. Seismic Sea Waves Tsunami) :
a series of huge waves that can cause major
devastation and loss of life when they hit the coast.
The word tsunami is a Japanese word which means
'harbor waves' (tsu - harbor, nami - waves).
The possible causes of a tsunami are an
underwater earthquake with the Richter scale
magnitude of over 6.75, sub marine rock
slides, volcanic eruptions or if an asteroid or a
meteoroid crashes into the water from the space.

• When such a large volume of water is moved, the
resulting wave is very large and can be spread
over an area of a hundred miles. This wave can
travel from the point of origin to the coast at
great speed. A tsunami has been known to travel
with speeds as high as 600 mph in the open
ocean. a tsunami can move from one end of the
ocean to the other end in a few hours!


• With the advance in technologies over the
years, tsunamis can now be detected before they
hit the coast thereby reducing loss of life.
Fortunately, tsunamis are very rare with
approximately six of them hitting the coast every
century, most of them occurring in the Pacific
Ocean.


Tsunami damage in Hilo, Hawaii.


(6-2) The Great Sumatra-Andaman Earthquake/Tsunami

• Since 1945, more people have been killed by
tsunamis than earthquakes. A tsunami event
that occurred recently and received global
news coverage was the catastrophic tsunami
that was generated in the Indian Ocean on
December 26, 2004. The epicenter of the
earthquake that triggered the series of
tsunami’s was located off the west coast of
Sumatra, Indonesia. More than 225,000
people in 11 countries were killed. The waves
were up to 100 feet high

• The earthquake was the 2nd largest ever
recorded on a seismograph at ~9.2 on the
Richter scale and it cause the entire planet to
vibrate up to 1 centimeter, causing smaller
earthquakes in other parts of the world.
• The tsunami took anywhere from 15 minutes
to 7 hours to reach the various coastlines that
were devastated.
• In the minutes preceding the tsunami
wave, the sea withdrew from the shores by
nearly 2 miles, attracting people to the beach
with fatal consequences.

• References:
• Earthquake Causes and Characteristics
• Fergany, E.A.; Sawda S. (2009). "Estimation of Ground Motion at
Damaged Area During 1992 Cairo Earthquake Using Empirical
Green's Function“ .
• South Carolina Department of Education 2005.
• Klinger, Yann; Rivera, Luis; Haessler, Henri; Maurin, JeanChristophe (August 1999) , "Active Faulting in the Gulf of Aqaba:
New Knowledge from the Mw 7.3 Earthquake of 22 November
1995”

• Mohamad,, Abdul, Gomez, Francisco; Muawia et al
(2000), "Remote Earthquake Triggering along the Dead Sea
Fault in Syria following the 1995 Gulf of Aqaba Earthquake.

• https://www.eeri.org/category/learning-fromearthquakes/egypt/.
• http://en.wikipedia.org/wiki/1995_Gulf_of_Aqaba_earthquake
• http://www.buzzle.com/articles/richter-scale-for-kids.html

Earthquakes

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