2. INDEX
Earthquake Terminology
Causes of Earthquake
Forecasting of Earthquake
Classification of Earthquake
Effects of Earthquake
Magnitude and Intensity
Principles of Planning of Building
Precautions for Earthquake
3. 1. Earthquake Terminology
Focus :
The point within the earth where earthquake rupture starts is called
focus or hypocentre.
It is the source of elastic waves inside the earth.
4. Epicentre :
The point on the earth’s surface vertically above the focus of the
earthquake is called epicentre.
Focal depth :
The depth of the focus from the epicentre is called focal depth.
It is an important parameter in determining the damaging potential of
earthquake. Most of the damaging earthquake have shallow focus with
focal depth less than 70 km.
Epicentral distance :
The distance from the epicentre to any point if interest in the surface of
the earth is called epicentral distance or focal distance.
5. Foreshocks :
A number of smaller size earthquake take place before and after a big
earthquake. Those occuring before the big one are called foreshocks.
Aftershocks :
Smaller size earthquakes occuring after the main shocks are called
aftershocks.
Focal region :
Seismic destruction propagates from the focus through a limited region of
the surrounding earth’s body, which is called the focal region.
6. 2. Causes of earthquake
Momentary shaking of the ground or vibrations or oscillations of
the ground caused by the slip or by volcanic or magmatic
activity or other sudden changes in the earth are called
earthquakes.
Seismic Sources
Natural sources Man made sources
1. Tectonic earthquakes 1. Controlled sources
2. Volcanic earthquakes i. Chemical explosives
3. Plutonic earthquakes ii. Nuclear explosives
4. Land slides 2. Reservoir induced earthquakes
5. Collapse of cavity 3. Mining induced earthquakes
4. Cultural noise
( Industry, Traffic, etc.)
7. 3. Forecasting of Earthquake
Natural calamities like heavy rain, flood, cyclone, tsunami, etc. can be
predicted in advance. But, no scientific technique is available for
prediction of earthquake.
The prediction of earthquake is almost impossible. The scientists make
prediction of earthquake based on various analysis and assumption.
Various predictions are :
From the study of location of past earthquake, intensity, time duration,
geological condition, etc.
Abrupt change in water level in ponds, lakes, etc.
From the study of changes in ground water level
From ground tilting study
From the study of main shocks, fore shocks, after shocks.
Ground slope changes
Increase in volume of rocks, level of random gas level in deep wells and in
electric conductivity of rocks.
From strange behavior of animals and birds.
8. 4. Classification of Earthquake
The various basis of classification of earthquakes are as under :
a) Based on location :
Based on location the earthquake are classified as,
1. Interplate earthquake :
Most earthquake in the world occur along the boundaries of the tectonic
plated and are called interplate earthquakes.
About 99 % earthquakes are interplate earthquakes.
e.g. 1897 – Assam earthquake
1905 – Kangra (H.P.)
1950 – Assam earthquake
9. 2. Intraplate earthquake :
A number of earthquakes also occur within the plate itself away from the plate
boundaries, are called intraplate earthquake.
About 1% earthquakes are intraplate earthquakes.
e.g. 1993 – Lature earthquake
1967 – Koyna earthquake
b) Based on focal depth :
Based on focal depth the earthquakes are classified as below :
Earthquake Focal depth
Shallow earthquake < 70 km
Medium earthquake 70 to 300 km
Deep earthquake >300 km
10. c) Based on size or Magnitude :
Earthquake are often classified into different groups based on their
size as given in table below :
Group Magnitude Annual Average Number
Great 8 and higher 1
Major 7 – 7.9 18
Strong 6 - 6.9 120
Moderate 5 – 5.9 800
Light 4 – 4.9 6200 (estimated)
Minor 3 – 3.9 49000 (estimated)
Very minor < 3.9
M2.3 – 1000/day,
M1.2 – 8000/day
11. d) Based on epicentral distance :
Based on epicentral distance, the earthquakes are classified as under
:
1. Local earthquake - < 1°
2. Regional earthquake – 1° – 10°
3. Teleseismic earthquake - > 10°
12. 5. Effects of earthquake
Primary effects
Secondary effects
• Primary Effects :
• Effects related with origin of earthquake are known as primary effects.
Primary effects are directly connected with geology and topography.
• Primary effects are :
• Change in topography
• Formation of new hills
• Change in direction of existing water course
• Formation of new water course
• Wrapping of strata
• Formation of sand dyke
• Formation of huge cracks in land
• Change in under ground water level
13. Secondary Effects :
Secondary effects are caused due to passage of seismic waves and are
associated with ground shaking.
Secondary effects are :
Destruction of human lives
Destruction of multistoried buildings
Destruction of dams and bridges
Landslides and mudslides
Uprooting of trees
Psychological effects on human beings
Worst effect on communication system
Damage to road and railway lines
Destruction of telephone and TV tower
Huge waves in the sea (Tsunami)
Fire by damaging gas lines and snapping electric wires
14. 6. Magnitude and Intensity
Magnitude
1. Magnitude of an
earthquake is a measure
of amount of energy
released during and
earthquake.
2. It is the quantitative
measure of the actual
size of the earthquake.
3. For a particular
earthquake magnitude is
same for all the places.
4. It is more precise
measure of earthquake.
Intensity
1. The intensity of
earthquake is a measure
of the actual ground
shaking at a location
during an earthquake.
2. It is the qualitative
measure of the size if
the earthquake.
3. For a particular
earthquake intensity of
earthquake decreases
with distance from the
epicenter.
4. It is less precise than
magnitude.
15. 7. Principles of planning of buildings
Building configurations :
Configuration requirements of a structure :
• From a planner point of view, as a precursor to the design analysis, the
configuration requirements preferred as far as possible are listed below.
• The structure should,
Be simple and symmetrical.
Be not too elongated in plan or elevation.
Have uniform and continuous distribution of strength, mass and stiffness, so that
centre of mass and centre of stiffness are close to each other.
Be without re-entrant corners.
Have sufficient ductility.
Be preferably without large projections.
Be without external elevator shafts and staircase wells as they are undesirable
and tend to act on their own in earthquakes.
Have horizontal members which form hinges before the vertical members.
16. Wall opening :
Opening in wall should be small and at center.
Opening from internal corners should be at ¼ height or opening, which
should not be less than 60 cm.
Opening should not be more than,
1 storey = length of wall between two cross wall 50 %
2 storey = 42 %
3 storey = 33 %
Horizontal distance between two openings, should not less than half of
height of short opening or 60 cm.
Vertical distance should not less than half of width of short opening or 60
cm.
17. 8. Precautions for Earthquake
What to Do Before an Earthquake :
Make sure you have a fire extinguisher, first aid kit, a battery-
powered radio, a flashlight, and extra batteries at home.
Learn first aid.
Learn how to turn off the gas, water, and electricity.
Make up a plan of where to meet your family after an
earthquake.
Anchor heavy furniture, cupboards, and appliances to the walls
or floor.
Learn the earthquake plan at your school or workplace.
18. What to do during an earthquake :
Stay calm ! If you're indoors, stay inside. If you're outside, stay
outside.
If you're indoors, stand against a wall near the center of the
building, stand in a doorway, or crawl under heavy furniture (a
desk or table). Stay away from windows and outside doors.
If you're outdoors, stay in the open away from power lines or
anything that might fall. Stay away from buildings (stuff might
fall off the building or the building could fall on you).
Don't use matches, candles, or any flame. Broken gas lines and
fire don't mix.
If you're in a car, stop the car and stay inside the car until the
earthquake stops.
Don't use elevators (they'll probably get stuck anyway).
19. What to do after earthquake :
▪ Check yourself and others for injuries. Provide first aid for anyone
who needs it.
▪ Check water, gas, and electric lines for damage. If any are damaged,
shut off the valves.
▪ Check for the smell of gas. If you smell it, open all the windows and
doors, leave immediately, and report it to the authorities.
▪ Turn on the radio. Don't use the phone unless it's an emergency.
▪ Stay out of damaged buildings.
▪ Be careful around broken glass and debris. Wear boots or sturdy
shoes to keep from cutting your feet.
▪ Be careful of chimneys.
▪ Stay away from beaches. Tsunamis and seiches sometimes hit after
the ground has stopped shaking. Stay away from damaged areas.
