(1) Causes of earthquake (2) Seismic waves Body waves Surface waves (3)Locating and measuring Earthquakes Determining the location of earthquake Measuring the size of earthquake Location and size of earthquake in United States

1. BISMILLAHIRRAHMANIRRAHIM
Afnan Ullah
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2. Objectives
(1) Causes of earthquake
(2) Seismic waves
Body waves
Surface waves
(3)Locating and measuring Earthquakes
Determining the location of earthquake
Measuring the size of earthquake
Location and size of earthquake in United States
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3. Earthquake
A sudden violent shaking of the ground, typically causing great
destruction, as a result of movements within the earth's crust or
volcanic action
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4. Causes of eartquake
• Earthquakes are caused by tectonic movements in the Earth's
crust. The main cause is that when tectonic plates collide, one
rides over the other, causing orogeny (mountain building),
earthquakes and volcanoes.
• The boundaries between moving plates form the largest fault
surfaces on Earth. When they stick, relative motion between
the plates leads to increasing stress. This continues until the
stress rises and breaks, suddenly allowing sliding over the
locked portion of the fault, releasing the stored energy as
shock waves.
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5. Causes of the earthquakes fall into the following
broad categories:
• 1. Volcanic activities
• 2. Folding and faulting
• 3. Plate tectonics
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6. Volcanic activities
Volcanic explosions are certainly the most common cause of
earthquakes in the neighbourhood of active volcanoes. Such
earthquakes are, therefore, known as volcanic earthquakes.
This type of earthquake is caused either under the influence of the
increasing pressure of volcanic gases or the subterranean
movement of molten lava trying to come up on the earth's surface.
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7. Folding and Faulting
A fault is defined as a fracture plane along which the rocks have
been displaced. There are vertical as well as horizontal
displacements. Earthquakes are caused due to sudden movements
of rocks along faults. Such earthquakes are called tectonic
earthquakes.
Remember that the horizontal as well as vertical movements of
rocks result from the operation of endogenetic forces beneath the
earth's surface. It is due to such movements that folds and faults
are created.
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8. Plate Tectonics
According to the theory of plate tectonics, the surface of the earth
consists of 15 plates comprising the rigid upper mantle, and the
oceanic and continental crust. Out of the total number of plates, 6
are major plates and 9 are minor plates.
These plates are always moving. Now, it is an established fact
that practically all the tectonic, seismic and volcanic activities
take place at the plate margins. That is why must of the
earthquakes and volcanoes are found in narrow and semi-
continuous belts mostly confined to the plate boundaries.
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9. Seismic waves
Energy moving outward from the focus of an earthquake
OR
A wave of energy that is generated by an earthquake or other
earth vibration and that travels within the earth or along its
surface.
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10. Seismic Waves forms
1. Body Waves:Waves travel through the earth interior,spreading
outward from the focus in all directions
There are two types of body waves
P-waves:
– called compressional, or push-pull waves
– Propagate parralel to the direction in which the wave is
moving
– Move through solids, liquids
S-waves:
– Called shear waves
– Propagate the movement perpendicular
to the direction in which the wave is
moving7/18/2018 10

11. cont...
2. Surface Waves:Waves
that travel on earth's surface
away from the epicentre,like
water waves spreading out
from a pebble thrown into
pond.
There are two types of
earthquake
• Love waves:The ground
move side to side in a
horizontal plane that is
perpendicular to the
direction the wave is7/18/2018 11

12. Measuring earthquakes
• Seismometers:
instruments that detect
seismic waves
Seismographs: Record intensity, height
and amplitude of seismic
waves
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13. Locating the shaking
• Measure time between P and S waves on a seismogram
• Need at least 3 seismographs
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14. Frequency of Occurrence of Earthquakes
Descriptor Magnitude Average Annually
Great 8 and higher 1 ¹
Major 7 - 7.9 17 ²
Strong 6 - 6.9 134 ²
Moderate 5 - 5.9 1319 ²
Light 4 - 4.9
13,000
(estimated)
Minor 3 - 3.9
130,000
(estimated)
Very Minor 2 - 2.9
1,300,000
(estimated)
¹ Based on observations since 1900.
² Based on observations since 1990.
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15. Recent Earthquake Activity in the World
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16. Largest earthquake in the world
Chile : 1960 May 22 19:11:14
UTC
Magnitude 9.5
•More than 2,000 killed, 3,000 injured,
2,000,000 homeless, and $550 million
damage in southern Chile
• tsunami caused 61 deaths
•$75 million damage in Hawaii;
• 138 deaths and $50 million damage
in Japan;
•32 dead and missing in the
Philippines;
and $500,000 damage to the west coast
of
the United States.
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17. Most Destructive Known Earthquakes on Record in the
World
Date Location Deaths Magnitude Comments
May 31, 1970 Peru 66,000 7.9 $530,000,000
damage, great rock
slide, floods.
July 27, 1976 China,
Tangshan
255,000
(official)
7.5 Estimated death toll as
high as 655,000.
Sept 19, 1985 Mexico
Michoacan
9500
(official)
8.0 Estimated death toll as
high as 30,000
Old lake bed magnified
shock waves by 500%
2001 Jan 26 India 20,023 7.7 166,836 injured,
600,000 homeless
.
2004 Dec 26 Sumatra 283,106 9.0 Deaths from earthquake
and tsunami
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18. Location and size of earthquakes in the United
States
According to thr
U.S.Geological servey,
earthquake pose a
significant risk to 75
million people in 39 states.
Most of the large
earthquakes occur in the
western states.
Quakes in California, Utah,
Idaho, Montana,
Washington and other
western states are related to
known faults and usually
involve surface rupture of
the ground.
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19. Cont....
Earthquake east of the Rocky Mountain rarer and generally
smaller and deeper than earthquakes in the western United States.
Although large quakes are extremly rare in the central and eastern
United States, when they do occur they can be very destructive
and widely felt, b/c earth crust is older, cooler and more brittle in
the east then in the west and seismic wave travel more efficiently
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