EARTHQUAKES : CAUSES AND PREDICTIONS by Prof. R. N. Tiwari Department of Geology Banaras Hindu University
Worst natural hazard
Impact over a large area
Causing destruction on massive scale
Loss of human life and property
Devastation is quick and sudden
No time to escape
Lisbon – 1755
Last two decades – (1982-2000) 26 major earthquakes- casualities-150000
Occurrence of earthquakes- frequent
No body can remain without being affected
Every time people get panic
Series of questions arise
An earthquake is vibration of earth produced by rapid release of energy
Energy released radiates in all directions from its source
Energy is in the form of waves
Sensitive instruments around the world record the event
Longitudinal (P) Waves
Highest velocity, 5-7 km./ sec.
Can travel solid and liquid both
Transverse (S) Waves
Do not pass in liquid and gases
Surface (L) Waves
Travel along outer part of earth with great amplitude and slowest velocity
Cause greatest destruction
Focus and Epicentre
Focus : The place in the earth crust where the earth shocks occur
Epicenter : The point at the surface immediately above the focus.
Location of Epicenter
The time intervals between the first arrivals of P and S waves are used to determine the distance between a seismograph and the earthquake epicenter
Three or more stations are needed to determine the location of an earthquake .
Seismograph: Instrument to design to register earthquake waves Seismogram : Recording of earthquake waves on a paper
Magnitude And Intensity Of Earthquakes
The severity of an earthquake can be expressed in several ways.
Magnitude and Intensity measure different characteristics of earthquakes.
Intensity measures the strength of shaking produced by the earthquake at a certain location. It is determined from effects on people, human structures, and the natural environment .
Magnitude measures the energy released at the source of the earthquake. It is determined from measurements on seismographs and usually expressed by the Richter Scale
< 2 Generally not felt but recorded
2.0 – 2.9 Potentially perceptible
3.0 – 3.9 Felt by some
4.0 – 4.9 Felt by most
5.0 – 5.9 Damaging shocks
6.0 – 6.9 Destructive in populated regions
7.0 – 7.9 Major Earthquakes; Inflict serious damages
>8 Great Earthquakes; cause extensive
destruction near epicenter
( Maximum known 8.9 )
Magnitude / Intensity Comparison Magnitude Typical Maximum Modified Mercalli Intensity 1.0 - 3.0 I 3.0 - 3.9 II - III 4.0 - 4.9 IV - V 5.0 - 5.9 VI - VII 6.0 - 6.9 VII - IX 7.0 and higher VIII or higher
Effects of Earthquakes
1. Loss of human life and property
2. Displacement of roads, rails, canals,
bridges, dams, etc.
3. Landslides, formation of lake, change of
4. Liquefaction where ground is very wet with
higher water table, common in coastal
5.Tsunamis occur following violent movement of
the sea floor generated by seismic sea waves.
Liquefaction in Japan
Seismic waves moving large bodies of water
Result from vertical displacement along a fault located on ocean floor
• In the deep ocean the waves may go by unnoticed (low wave height)
• Wave speed 800 km/hr
Shallow water – Height exceeds 30m.
Earth - one of the nine planets of solar system
Originated about 4500-4600 M.Y.
Today continents are separated by ocean
About 250 my. There was one continent and one ocean called Pangaea and Panthalasa
About 200my. Pangaea split into two major continents- Laurasia and Gondwana land
Indian plate travelled 9 m per century
Collided with Eurasia plate- 40-50my.
Formation of Himalaya
Seismic waves revealed – earth has radially layered structure
Three main divisions- Crust, Mantle and Core
Each layer has distinctive physical chemical and seismic characters
Mechanical division of Earth
100-150 km. below Continent
70-100 Km. below Ocean
More rigid – forming hard outer shell
Divided in to several large fragments- called Plates
150 Km. thick, lies beneath lithosphere
Lower rigidity partly molten
Twelve major plates
Antarctica, Africa, Eurasia, India, Australia, Arabia, Philippines, North America, South America, Pacific, Nazca and Cocos
Earthquake occurs on plate margins
Associated with interaction between plates
Types of Plate Margin
Constructive (divergent) plate margin
Spreading centre, plate moving a part
Destructive (convergent) plate margin
Subduction zone, One plate forced under another, Plates bent sharply
Conservative plate margin:
Formed by transform fault
Lithosphere is neither created nor destroy
Convection current generated in the mantle moves the plates
Cause of Earthquakes
Brittle condition of the lithosphere causes fracture when strongly stressed
Rupture produces an earthquakes
A violent release of elastic energy due to sudden displacement on a fault plane
Cause of Earthquakes • Moving Plates • Release of energy from within the Earth
Earthquakes and Fault
Movements that produced earthquakes are usually associated with large fractures in earth’s crust called faults
Motion along faults can be explained by plate tectonic theory
Fault: A fracture or system of fractures along which rocks have been displaced.
Types of Fault
Mechanism for earth quakes was explained by H.F. Reid
Rocks on both side of an existing fault are deformed by tectonic forces
Rocks bend and store elastic energy
Frictional resistance holding the rocks together is overcome
Slippage at the weakest point (focus) occur
Vibrations (earthquakes) occur at the deformed rock “ springs back” to its original shape (elastic rebound)
Earthquakes are generally distributed in belts . Eighty percent of the world's earthquakes occur in the circum-Pacific belt. Earthquakes also occur on the Mediterranean-Himalayan belt, and along other plate boundaries.
• Developing in seismically active areas?
• Building codes
• Emergency response
Base isolation designs
• The natural world is unpredictable!
Animal behavior – Dogs barking excessively
– Pigs not eating climbing walls
– Cats left buildings
– Rats/mice left hidings places
Elevation changes in land surface
Groundwater level changes
Earthquake prediction may be possible by
Measuring ground tilt,
Changes in the earth’s magnetic field
Presence of radon gas in wells.
No reliable method exist for making short range earthquake prediction
Long term predictions based on occurrence of earthquakes on a time scale-30-100 years or more.
Using historical record on paleoseismology
Disaster Management Programme
Cultivate a culture of disaster preparedness.
Think about disaster management as a regular, day to day thing
Disaster planning should begin at home
School children should be taught basic safety measures
Radio, TV., can be used to explain these things
Designs of building should be earthquake safe and must be approved by competent authority.
Identify bad building and get them repaired.
Preventive measures against building collapse
Houses should have a uniform square or a rectangular plan
The L/B ratio should be from 0.15 to 0.20
Foundation / plinth should be at least 1.5 times thicker than the wall
Doors and windows should be placed at corners of the room, 24 inches away from the room edges, minimum gap of 60cm. Between doors and windows
Mortar ratio – Cement: sand = 1:6
- Cement: lime: sand = 1:2:9
R.C.C. bands should be used at chair, door and roof levels
Window porches and roofs should protrude minimal
Jambs should be placed at corners between walls to provide strength and elasticity
Iron rods should be vertically placed in corners
Houses build of stone- wall should not be thicker than 45 cm. and R.C.C bands should used at each stage.
Above all, the material used should be of good quality----after all it is your sweet home