PRESENTED BY-MISS DEBASREE PURKAYASTHAGUIDED BY-DR. S.K.PAL.

EARTHQUAKE An earthquake is the vibration of Earth produced by the rapid release of accumulated energy in elastically strained rocks

Energy released radiates in all directions from its source, the focus . Energy propagates in the form of seismic waves . Sensitive instruments around the world record the event .

LAYERS OF EARTH Crust:

Continental crust (25-40 km)

Oceanic crust (~6 km) Mantle

Upper mantle (650 km) Lower mantle (2235 km)

Core Outer core: liquid (2270

km) Inner core

Values in brackets represent the approximate thickness of each layer

THEORY OF PLATE TECTONICS The theory of Plate tectonics was proposed in 1960s based on the theory of continental drift.

This is the Unifying theory that explains the formation and deformation of the Earth’s surface.

According to this theory, continents are carried along on huge slabs (plates) on the Earth’s outermost layer (Lithosphere).

Earth’s outermost layer is divided into 12 major Tectonic Plates (~80 km deep). These plates move relative to each other a few centimeters per year.

TECTONICS PLATES OF EARTH

TYPES OF PLATE BOUNDARIES Divergent plate

boundaries: where plates move

apart Convergent Plate

boundaries: where plates come

together Transform plate

boundaries: where plates slide past each other

CAUSES OF EARTHQUAKEMovement of Tectonic Plates

Earth is divided into sections called Tectonic plates that float on the fluid-like interior of the Earth. Earthquakes

are usually caused by sudden movement of earth plates

Rupture of rocks along a fault

Faults are localized areas of weakness in the surface of the Earth, sometimes

the plate boundary itself

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

ELASTIC REBOUND THEORYExplains 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.

SEISMIC WAVESWhen a earthquake occurs, two types of seismic waves are generated:- Body waves, that travel through the interior of the earth. They are of two types- P-wave- primary waves or

push-pull waves or compression waves.

S-waves- shear waves, secondary waves or traverse waves.

Surface waves, that travel along the surface layers of the earth. They are of two types- Love wavesRayleigh waves

STRENGTH OF AN EARTHQUAKE• INTENSITY Qualitative measure of an

earthquake which describes the effect of an earthquake at a particular location.

Isoseismal lines identify areas of equal intensity.

It is measured by modified-mercalli intensity scale.

Intensity changes with distance from epicenter of earthquake.

• MAGNITUDE Quantitative measure of the

earthquake which is related to the amount of energy released to cause the earthquake.

It is measured by Richter scale and Seismograph.

Magnitude is same for a particular earthquake.

STRONG GROUND MOTION

PEAK GROUND MOTION

DURATION OF GROUND MOTION

FREQUENCY CONTENT

STRONG GROUND MOTION MEASUREMENT BY ACCELEOGRAPHS

They are the instruments used to record strong ground motion i.e. motion large enough to be potentially damaging.These instrument record acceleration of the ground as a function of time.Triaxial acceleographs are able to measure ground motion in two perpendicular horizontal directions and in the vertical directions.

VARIOUS TYPES OF ACCELEOGRAPHS

1. K2 ACCELEOGRAPH

2. FBA-23 3. STS-1

FACTORS INFLUENCING GROUND MOTION

EARTHQUAKE MAGNITUDE EPICENTRAL DISTANCE LOCAL SOIL CONDITION CHARACTERISTIC OF LOCAL GEOLOGY ALONG

THE PROPAGATION PATH SOURCE MECHANISM OF THE EARTHQUAKE

SEISMIC HAZARDS INTERNAL FORCES DUE TO LARGE PEAK GROUND ACCELERATIONS CAUSES STRUCTURAL FAILURE, LANDSLIDES, RETAINING WALL FAILURE.

LIQUEFACTION OF SATURATED SOIL CAUSES STRUCTURAL FAILURES, LARGE LATERAL DISPLACEMENT OF SLOPES, INCREASED LATERAL PRESSURE ON RETAINING WALL

EARTHQUAKE INDUCED FIRE CAUSES LOSS OF PROPERTY

EARTHQUAKE INDUCED WATER WAVES KNOWN AS TSUNAMIS CAUSE SUBMERGENCE OF SHORE AREAS CAUSING DEATH AND LOSS OF PROPERTY

RARELY THERE MIGHT BE A PERMANENT CHANGE IN GROUND ELEVATION

CONCLUSION

PREDICTING EARTHQUAKES Strange Animal Behavior

stress in the rocks causes tiny hairline fractures to form, the cracking of the rocks evidently emits high pitched sounds and minute vibrations imperceptible to humans but noticeable by many animals.

Foreshocks

unusual increase in the frequency of small earthquakes before the main shock

Changes in water level

porosity increases or decreases with changes in strain

Seismic Gaps

based of the chronological distribution of major earthquakes

PROTECTING AGAINST EARTHQUAKE DAMAGE

Prepare a Seismic Risk Map for the globe which identifies rock types, liquefaction potential, landslide potential.

Extensive geologic surveying has to be done to identify all active faults, including hidden faults.

Earthquake Resistant Design of StructuresEnact building codes to design and build earthquake-resistant structures in high seismic risk areas. wood, steel and reinforced concrete are preferred as they tend to move with the shaking ground (unreinforced concrete and heavy masonry tend to move independently and in opposition to the shaking, battering one another until the structure collapses)

Critical facilities such as nuclear power plants and dams should be built on stable ground and as far as possible from active faults.

THANKS FOR UR ATTENTION