EARTHQUAKE

Submitted by:Himanshu Rajput(13363)Mechanical Engineering

Department NIT Hamirpur

When Earth and building, are about to shake,Be Ready to face it, as it is EARTHQUAKE.

• An Earthquake is the result of a sudden release of energy in the Earth’s crust that creates seismic waves(vibrations).

• Earth’s crust is in constant motion because of tectonic forces.

• Earth’s crust can store elastic energy.• When forces exceed the elastic limits and structural

strength of the rocks, the rocks will break and/or move producing vibrations that travel outward in all directions.

WHAT IS AN EARTHQUAKE ?

EPICENTER AND FOCUS

The actual place underground where the rocks break producing vibrations is called the Focus.

The place on the surface directly above the focus is called the Epicenter.

PLATE TECTONICST h e c o n v e c t i v e fl o w s o f m a n t l e m a t e r i a l

c a u s e t h e c r u s t a n d s o m e p o r t i o n o f t h e m a n t l e , t o s l i d e o n t h e h o t m o l t e n o u t e r c o r e . T h i s s l i d i n g o f e a r t h ’ s m a s s t a ke s p l a c e i n p i e c e s c a l l e d t e c t o n i c p l a t e s .

T h e s u r f a c e o f t h e e a r t h c o n s i s t s o f s e v e n m a j o r t e c t o n i c p l a t e s a n d m a n y s m a l l e r o n e s . T h e s e p l a t e s m o v e i n d i ff e r e n t d i r e c t i o n s a n d a t d i ff e r e n t s p e e d s f r o m t h o s e o f t h e n e i g h b o u r i n g o n e s .

T h e m o v e m e n t o f t e c t o n i c i s v e r y s l o w b u t i n s o m e p l a c e s i t i s a s m u c h a s a b o u t 5 c m p e r y e a r.

Earthquakes often occur when tectonic plate collide.

What happens when plates collide? It depends how the plates are moving when they meet:

When two plates collide head-on, they push each other up and form mountains. That's how the Himalayas and other great mountain ranges (including the Rockies, long ago) were created.

FAULTS A f a u l t i s a f r a c t u r e w i t h i n s o m e

p a r t i c u l a r r o c k y m a s s i n s i d e t h e e a r t h ' s c r u s t . T h e d e p t h a n d l e n g t h o f f a u l t s v a r y g r e a t l y.

Fa u l t s m ay r a n g e i n l e n g t h f r o m f e w m e t e r s t o m a n y k i l o m e t e r s a n d a r e d r a w n o n a g e o l o g i c a l m a p a s c o n t i n u o u s o r b r o k e n l i n e s . E a r t h q u a k e s a r e c a u s e d b y a c t i v e f a u l t s , t h a t i s , f a u l t s a l o n g w h i c h t h e t w o s i d e s o f t h e f r a c t u r e m o v e w i t h r e s p e c t t o e a c h o t h e r. S o , a n e a r t h q u a k e i s c a u s e d b y t h e s u d d e n m o v e m e n t o f t h e t w o s i d e s o f a f a u l t w i t h r e s p e c t t o a n o t h e r .

TYPES OF FAULTS:

Faults Are Classified According to the Kind of Motion That Occurs on them:1. Strike slip fault2. Dip slip fault

Shear Force: A system of forces that operates against a body from different sides. Makes a strike-slip fault. It is of two types:

STRIKE-SLIP FAULT

1. Right lateral 2. Left lateral

Strike-Slip Fault

Compression Force: Force pushing something together. Makes a reverse fault.

Dip-Slip Fault

1. Normal 2. Reverse

Normal Fault Structures

Reverse Fault Structures

Originate at the focus and travel outward in all directions

Foreshocks: small earthquakes that come before a major earthquake.

Aftershocks: Are adjustments in the crust after in earthquake.

o Smaller than main earthquake, but can cause as much or more damage. They can continue for weeks to months. Not every earthquake produces aftershocks.

SEISMIC WAVES

Types of seismic waves:1. Body waves -- travel through interior 2. Surface waves -- travel on surface of earth Specific Body WavesPrimary or "P" Waves: Primary waves Highest velocity Causes compression and expansion in direction of wave travel. Secondary or "S" Waves: Secondary or shear waves Slower than P waves but faster than surface waves. Causes shearing of rock perpendicular to direction of wave propagation Cannot travel through liquids  Surface Waves or "Love" (“L”) WavesCause vertical & horizontal shakingTravel exclusively along surface of earth

PRIMARY OR “P”WAVE

SECONDARY OR “S” WAVE

Rayleigh WavesThe other kind of surface wave is the

Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.

MEASUREMENT OF EARTHQUAKE

Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram.

MAGNITUDE OF AN EARTHQUAKEMagnitude -- measure of energy released during

earthquake.There are several different ways to measure magnitude.

Most common magnitude measure is Richter Magnitude, named for the renowned seismologist,

Charles Richter.  

RICHTER MAGNITUDEMeasure amplitude of largest wave on seismograph

record. Take into account distance between seismograph &

epicenter.  

Logarithmic numerical (NOT a physical) scale.

Increasing one whole unit on Richter Scale represents 10 times greater magnitude.

Going up one whole unit on Richter Scale represents about a 30 times greater release of energy.

RICHTER SCALE

INTENSITY OF EARTHQUAKEIntensity refers to the amount of damage done in an earthquake.Mercalli scale is used to express damage.

MODIFIED MERCALLI INTENSITY SCALE: An estimate of the intensity based on

observation of actual damage.• A 12 point scale using roman numerals.• Very dependent upon the quality of

structures.

The Secondary effects of earthquakes include the following:

Shaking and ground ruptureLandslides FiresTsunamiFloodsHuman impactsRadiation LeakageSoil liquefaction

Intensity of Earthquakes forces Lack of strength and integrity in buildings Resonance and semi-resonance Lack of ductility and lack of detailing

MAIN CAUSES OF DAMAGE

RESONANCE= frequency content of the ground motion is close to building's natural frequency ,tends to increase or amplify building response .Building suffers the greatest damage from ground motion at a frequency close or equal to its own natural frequency

Resonance & Semi-Resonance

Landslide after earthquake

The tsunami of the 2004 Indian Ocean earthquake

Ash cloud of Pinatubo during 1991 eruption

OBJECTIVE OF EARTHQUAKE ENGINEERING

The objective of earthquake engineering is to foresee the impact of earthquakes on buildings and other structures and to design such structures to minimize the risk of damage. Existing structures can be modified by seismic retrofitting to improve their resistance to earthquakes. Earthquake insurance can provide building owners with financial protection against losses resulting from earthquakes.Emergency management strategies can be employed by a government or organization to mitigate risks and prepare for consequences.

Order of increasing

risk

The above slides gave us various aspects related to earthquake. Now after these slides we know what is earthquake and way to measure its magnitude by Richter scale.The various seismic waveforms and Rayleigh waves. The slides also showed the after effects of earthquake like landslides, tsunami etc. and the destruction caused by earthquake. In the end it was the importance of Earthquake engineering.

Summary

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