EARTHQUAKE

Suchitra Laishram
MSc.II year
Panjab University

OBJECTIVES
 List the different types of seismic waves, their
different properties and describe how seismologists
can use them to learn about earthquakes and the
Earth's interior.
 Describe how to find an earthquake epicenter.
 Describe the different earthquake magnitude scales
and what the numbers for moment magnitude
mean.
 Describe how earthquakes are predicted and why
the field of earthquake prediction has had little
success.

WHAT ARE EARTHQUAKES?
 The shaking or trembling caused by the
sudden release of energy.
 Usually associated with faulting or
breaking of rocks.

STUDYING EARTHQUAKES
Seismology --The study of earthquakes and
the waves they create.
Seismologists --Scientists who study and
measure earthquakes to learn more about
them and to use them for geological
discovery.

SEISMOGRAPHS
 Modern day
scientists use a
instrument called a
seismograph to
record earthquakes.
 Seismogram is
a graph output by a
seismograph.
 This instrument
records earthquakes
using waves.
 The larger the waves
the larger the
earthquake.

ELASTIC REBOUND THEORY
 Explains how energy is
stored in rocks
 Rocks bend until the
strength of the rock is
exceeded.
 Rupture occurs and
the rocks quickly
rebound to an
undeformed shape.
 Energy is released in
waves that radiate
outward from the fault.

The Focus and Epicenter of an
Earthquake
 The point within Earth
where faulting begins
is the focus, or
hypocenter.
 The point directly
above the focus on
the surface is the
epicenter.

WHERE DO EARTHQUAKES
OCCUR AND HOW OFTEN?
 Abt 80% of all earthquakes occur in the circum-Pacific
belt.
 Most of these result from convergent margin activity.
 Abt 15% occur in the Mediterranean-Asiatic belt.
 Remaining 5% occur in the interiors of plates and on
spreading ridge centers.

SEISMIC WAVES
 Seismic waves are waves of
energy that travel through
the Earth's layers, and are a
result of an earthquake.
 Two types:
Body waves
-- Primary(p) waves and
-- Secondary(s) waves
Surface waves
-- Love waves and
-- Rayleigh waves

BODY WAVES
 Primary waves (p)
 fastest waves.
 travel through solids, liquids, or gases.
 compressional wave, material movement is in the
same direction as wave movement.
 Secondary waves(s)
 slower than P waves.
 travel through solids only.
 shear waves - move material perpendicular to
wave movement.

SURFACE WAVE
 Two types
 Love waves-- are horizontally polarized shear waves
existing only in the presence of a semi-infinite
medium overlain by an upper layer of finite
thickness.
 travel slightly faster than Rayleigh waves.
 Rayleigh waves--travel as ripples with motions that
are similar to those of waves on the surface of water
 They are slower than body waves.
 In the layered medium (like the crust and upper
mantle) it depends on their frequency and

TYPES OF EARTHQUAKES
 Tectonic Earthquakes --occur when rocks in
the earth's crust break due to geological forces
created by movement of tectonic plates.
 Volcanic Earthquakes occur in conjunction
with volcanic activity.
 Explosive Earthquakes result from the
explosion of nuclear and chemical devices.
 Collapse Earthquakes are small earthquakes
in underground caverns and mines.

CLASSIFICATION OF EARTHQUAKE
 Earthquakes are usually classified on the following
bases:
(a) Cause of origin;
(b) Depth of focus; and
(c) Intensity and magnitude of earthquake.

(A) CAUSE OF ORIGIN:
(i) Tectonic
Earthquakes occur when the plates move against
one another. This movement can create stress that
causes the Earth's exterior shell, the lithosphere, to
shift or break.
(ii) Non-tectonic earthquakes.
The non-tectonic earthquakes are mainly of three
types due to surface causes, volcanic causes and
collapse of cavity roofs .

(B) DEPTH OF FOCUS
(i) Surface-earthquakes : Surface-earthquakes are
those in which the depth of the focus is less than
10,000 metres.
(ii) Shallow-earthquakes : The earthquakes with the
hypocentre at a depth of 10 to 50.
(iii) Intermediate-focus earthquakes : When the
earthquake is originated at a depth of 50 to 300
Kms.
(iv) Deep-focus earthquakes : The deep-focus
earthquakes or the plutonic earthquakes are those
with hypocentres located at depths more than 300
kms. Majority of the deep focus earthquakes
originate between 500 and 700 kms.

(C) INTENSITY AND MAGNITUDE OF
EARTHQUAKES
 Rossi-Forrel's Scale
 Mercalli Scale
 Richter Scale

(I) ROSSI-FORREL'S SCALE
The 1873 version of the Rossi–Forel scale had
10 intensity levels:
I. Microseismic tremor
II. Extremely feeble tremor.
III. Feeble tremor.
IV. Slight tremor
V. Moderate tremor
VI. Strong tremor
VII. Very strong tremor.
VIII. Damaging tremor
IX. Devastating tremor.
X. Extremely high intensity tremor.

Magnitude
 Richter scale measures
total amount of energy
released by an
earthquake; independent
of intensity.
 Amplitude of the largest
wave produced by an
event is corrected for
distance and assigned a
value on an open-ended
logarithmic scale .

TYPES OF DAMAGE CAUSE BY
EARTHQUAKE
 Physical Damage
-- Landslides
-- Tsunamis
-- Fires
-- Mudslides
-- Liquefaction
 Structural Damage
-- Buildings Collapse
-- Roadways Collapse
 Emotional Damage
-- Deaths

CAN EARTHQUAKES BE PREDICTED?
 With the present state of scientific knowledge, it is
not possible to predict earthquakes and certainly
not possible to specify in advance their exact date,
time and location.
 However, a great deal of research is being
conducted to develop reliable prediction methods
such as
Unusual behavior of animal.
Radon gas emission.
Electro-magnetic variations, etc .

EARTHQUAKE PRONE AREA IN INDIA

TO DO BEFORE ,DURING ,AFTER
EARTHQUAKE
Before the Earthquake:
-- Learn first aid,Be prepared to act.
-- Stock up on emergency supplies.
-- Arrange your work area for safety.
During an Earthquake:
-- Remain calm as the quake occurs.
-- Don't use elevators.
-- Drop down; take cover under a desk or table and hold on.
After an Earthquake:
--Remain calm and reassuring.
-- ready to act without electricity or lights.
-- If you must leave a building, use extreme caution
-- Use telephones only to report a life-threatening
emergency.

HELPLINE GIVEN
 North and Central America UNESCO-HELP
Basins.
 Brazil National Water Agency Delegation.
 USACE Global and Climate Scientists Featured.
 PIANC USA Commissions.
 U.S. Geological Survey.
 U.S. Bureau of Reclamation and Sandia
National
 Upper Rio Grande Commissions.

EARTHQUAKE

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