introduction of earthquake

7/26/2019 Introduction of earthquake

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06/12/16 1

How does earthquake Occurs
http://b.tech/8th%20semester/How%20does%20Earthquake%20occur%20with%20explanation%20-%20Social%20Science%203D%20animation%20video%20in%20HD.mp4http://b.tech/8th%20semester/How%20does%20Earthquake%20occur%20with%20explanation%20-%20Social%20Science%203D%20animation%20video%20in%20HD.mp4


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Prepared By:- Prof. Anuj Chandiwala06/12/16 2


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An earthquake may be define as a wave like motion

generated by fores in onstant turmoil under surfae

layer of the earth !the lithosphere"# travelling through

the earth$s rust.

%t may also define as the vibration# sometimes violent#

of the earth$s surfae as a result of a release of energy

in the earth$s rust.

&his release energy an be aused by sudden

disloations of segments of the rust# volani

eruptions# or even e'plosions reated by humans.

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&he magnitude is a measure of the amount of energy

released# while the intensity is the apparent effet

e'periened at a speifi loation.

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WHY DO EARTHQUAKESWHY DO EARTHQUAKES

OCCUR?OCCUR?Fractures, faults

(nergy released

and propagates in

all diretions as

seismi waves

ausing

earthquakes

focusepice!e"

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THE EARTH A$D %TS %$TER%ORTHE EARTH A$D %TS %$TER%OR)ong time ago# a large olletion of material masses

oalesed to form the (arth.

)arge amount of heat was generated by this fusion# and

slowly as the earth ooled down# the heavier and denser

materials sank to the entre and the lighter ones rose to the

top.

&he differentiated (arth onsist s of the %nner Core

!radius *+,km"# the /uter Core !thikness *,,km"#

the 0antle !thikness *,km"and the Crust

!thikness *1 to 2km". 06/12/16 6


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&he %nner Core is solid and onsists of heavy metals !e.g.#

nikel and iron"# while the Crust onsists of light

materials !e.g.# basalts and granites".

&he /uter Core is liquid in form and the 0antle has the

ability to flow. At the Core# the temperature is estimated

to be *,13C# thepressure *2 million atmospheres and

density *+4.1 gm56 this is in ontrast to *,13C#

+atmosphere and +.1 gm5 on the surfae of the (arth.

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CRUSTCRUST Crust is also known as lithosphere.

%t is the thinnest outer solid shell.

&he thiknessof rust is about 1 to 2 km.

&he rust onsists of light materials e.g.# basalts and

granites.

&he density of materials is about +1 kg5m7.

&he temperature of the rust is about ,13 C and the

pressure within it + atmosphere.

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)A$T*E)A$T*E 0antle is also known as asthenosphere.

&he thiknessof mantle is about , km.

%t is omposed of hot# dense ultra basi igneous roks in

a plasti state. %t has the ability to flow.

&he density of materials is 1-8 kg5m7.

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CORECORE Core is also known as barysphere.

%t is the densest entral part of the earth.

%t is omposed of the inner ore and outer ore.

&he inner ore# +, km in radius# is solid and onsists of

heavy metals like nikel and iron. %ts density is +8#

kg5m7.

&he outer ore surrounding the inner ore is ,, km

thik. %t e'ists as a liquid of density +, kg5m7.

&he temperature at the ore is about ,13C and the

pressure is 2 9 +8atmosphere.

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C%RCU*AT%O$C%RCU*AT%O$ Convetion urrents develop in the visous 0antle# beause

of prevailing high temperature and pressure gradients

between the Crust and the Core# like the onvetive flow of

water when heated in a beaker.

&he energy for the above irulations is derived from the

heat produed from the inessant deay of radioative

elements in the roks throughout the (arth$s interior.

&hese onvetion urrents result in a circulation of the

earths mass; hotmolten lava omes out and the old rok

mass goes into the (arth. 06/12/16 13


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&he mass absorbed eventually melts under high

temperature and pressure and beomes a part of the

0antle# only to ome out again from another loation#

someday.

0any suh loal irulations are taking plae at different

regions underneath the (arth$s surfae# leading to

different portions of the (arth undergoing different

diretions of movements along the surfae.

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!a" Convetion urrents

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+*ATE TECTO$%CS+*ATE TECTO$%CS &he onvetive urrent!flow" of the mantle material auses

the rust and some portion of the mantle to slide on the hot

molten outer ore.

&his sliding of the earth$s mass takes plae in portions alled

tetoni plates.

&he surfae of the earth onsists of +, major tetoni plates#

, smaller tetoni plates and many filler plates.

&he major tetoni plates are the %ndo Australian plate# the

(urasian plate# the paifi plate# the Afrian plate# the orth

Amerian plate# the south Amerian plate# the Antarti plate#

et.

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SE%S)%C WA,ESSE%S)%C WA,ES )arge strain energy released during an earthquake

travels as seismi waves in all diretions through the

(arth$s layers# refleting and refrating at eah interfae.

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Arrival of ;eismi waves at a site

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&hese waves are of two types - body waves and surfae waves6

the latter are restrited to near the (arth$s surfae.

+-W.es-+-W.es- &hey are also known as primary# longitudinal or ompressional

waves.

P-waves are analogous to sound waves.

&hey are the fastest waves and are longitudinal in harater.

&hey an travel through all materials like solid# liquid or air.

%n P- km5se !granite" ? +.1 km5se

!water".

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S-W.es-S-W.es-

;-waves are analogous to eletromagneti waves.

&hey are transverse or shear waves.

&he partiles in ;-waves osillate at right angles to the diretion of

propagation of the wave.

&hey do not hange instantaneous volume of the material through

liquids.

;-waves are slower the P-waves. &heir veloity in granite is 4

km5se.

&he veloity of ;-waves is diretly proportional to the shear

strength of the material through whih they pass. &hey do not

travel through liquids# as they do not have any shear strength.

;-waves ause ma'imum damages to strutures by roking the

surfae in both hori@ontal and vertial diretions.06/12/16 24


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R.ei W.esR.ei W.es-- ayleigh wave makes a material partile osillate in an ellipti

path in the vertial plane with hori@ontal motion along

diretion of energy transmission.

&he veloity of ayleigh wave is very muh depend on the

Poisson$s ratio and is equal to ., =s.

&hese waves are produed by interation of P and ; waves

with earth surfae.

&hey propagation at the surfae of earth at low veloity andlow frequeny.

&hese waves are involved with both vertial and hori@ontal

motion of earth.

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*oe W.es-*oe W.es- %n love waves partile motion is in hori@ontal plane

and transverse to the diretion of wave propagation.

&hey do not have vertial omponent of veloity.

&hese waves generally tend to reate shearing or

breaking ruptures.

)ove waves are faster than ayleigh waves but an

not pass through water.

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)EASUR%$5 %$STRU)E$T)EASUR%$5 %$STRU)E$T &he instrument that measures earthquake shaking# a

seismograph# has three omponents the sensor# the

reorder and the timer.

&he priniple on whih it works is simple and is e'pliitly

refleted in the early seismograph a pen attahed at the

tip of an osillating simple pendulum !a mass hung by a

string from a support" marks on a hart paper that is held

on a drum rotating at a onstant speed.

A magnet around the string provides required damping to

ontrol the amplitude of osillations.06/12/16 30


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&he pendulum mass# string# magnet and support together

onstitute the sensor6 the drum# pen and hart paper

onstitute the reorder6 and the motor that rotates the

drum at onstant speed forms the timer.

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/ne suh instrument is required in eah of the two orthogonal

hori@ontal diretions. /fourse# for measuring vertial

osillations# the string pendulum.

%t is replaed with a spring pendulum osillating about a

fulrum. ;ome instruments do not have a timer devie !i.e.# the

drum holding the hart paper does not rotate". ;uh instruments

provide only the ma'imum e'tent !or sope" of motion during

the earthquake6 for this reason they are alled seismo-sopes.

&he analog instruments have evolved over time# but today#

digital instruments using modern omputer tehnology are more

ommonly used.

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&he digital instrument reords the ground motion on the

memory of the miroproessor that is in-built in the

instrument.

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STRO$5 5ROU$DSTRO$5 5ROU$D


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STRO$5 5ROU$DSTRO$5 5ROU$D

)OT%O$)OT%O$ ;haking of ground on the (arth$s surfae is a net

onsequene of motions aused by seismi waves

generated by energy release at eah material point within

the three-dimensional volume that ruptures at the fault.

&hese waves arrive at various instants of time# have

different amplitudes and arry different levels of energy.

&hus# the motion at any site on ground is random innature with its amplitude and diretion varying randomly

with time.

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CHARACTERISTICS OFCHARACTERISTICS OF


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CHARACTERISTICS OFCHARACTERISTICS OF

STRONG GROUNDSTRONG GROUND

MOTIONSMOTIONS &he motion of the ground an be desribed in terms ofdisplaement# veloity or a aeleration.

&he variation of ground aeleration with time reorded

at a point on ground during an earthquake is alled an

aelerogram.

&he nature of a aelerograms may vary depending on

energy released at soure# type of slip at fault rupture#

geology along the travel path from fault rupture to the

(arth$s surfae# and loal soil.06/12/16 3#


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&hey arry distint information regarding ground shaking6

peak amplitude# duration of strong shaking# frequeny

ontent !e.g.# amplitude of shaking assoiated with eah

frequeny" and energy ontent !i.e.# energy arried by

ground shaking at eah frequeny" are often used to

distinguish them. 06/12/16 36


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TERMINOLOGYTERMINOLOGY &he point on the fault where slip starts is the ous or

Dypoenter# and the point vertially above this on the

surfae of the (arth is the (pientre .

&he depth of fous from the epientre# alled as oal

Eepth# is an important parameter in determining the

damaging potential of an earthquake.

0ost of the damaging earthquakes have shallow fous

with foal depths less than about Fkm. Eistane from

epientre to any point of interest is alled epientral

distane. 06/12/16 3&


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A number of smaller si@e earthquakes take plae before

and after a big earthquake !i. e.# the 0ain ;hok".

&hose ourring before the big one are alled

oreshoks# and the ones after are alled Aftershoks.

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MAGNITUDEMAGNITUDE

0agnitude is a quantitative measure of the atual si@e ofthe earthquake.

Professor Charles ihter notied that

!a" at the same distane# seismograms !reords of

earthquake ground vibration" of larger earthquakes have

bigger wave amplitude than those of smaller earthquakes.

!b" for a given earthquake# seismograms at farther

distanes have smaller wave amplitude than those at lose

distanes.

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INTENSITYINTENSITY %ntensity is a qualitative measure of the atual shaking at

a loation during an earthquake# and is assigned as oman

Capital umerals.

&here are many intensity sales. &wo ommonly used

ones are the 0odified 0eralli %ntensity !00%" ;ale and

the 0;G ;ale.

Both sales are quite similar and range from % !least

pereptive" to 9%% !most severe".

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&he intensity sales are based on three features of shaking

pereption by people and animals# performane of

buildings# and hanges to natural surroundings.

&able gives the desription of %ntensity =%%% on 0;G

sale.

&he distribution of intensity at different plaes during an

earthquake is shown graphially using iso-seismals# lines

joining plaes with equal seismi intensity.

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Magnitude Intensity


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Magnitude Intensity

&he magnitude of an

earthquake is a measure of

amount of energy released

during an earthquake.

&he intensity of earthquake is

a measure of the atual

ground shaking at a loation

during an earthquake.

%t is the quantitative measure

of the atual si@e of the

earthquake.

%t is the quantitative measure

of the si@e of the earthquake.

or a partiular earthquake

magnitude is same for all the

plaes.

or a partiular earthquake

intensity of earthquake

dereases with distane from

the epientre.06/12/16 44


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%t is more preise measure of

earthquake.

%t is less preise than

magnitude.

0agnitude sales are#)oal magnitude sale !0)".

;urfae wave magnitude !0s".

Body wave magnitude !mb ".

0oment magnitude !0w".

Euration magnitude !0E".

%ntensity sales are#0odified 0eralli %ntensity

!00%" sale.

0;G sale.

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BASIC GEOGRAPHY ANDBASIC GEOGRAPHY AND


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BASIC GEOGRAPHY ANDBASIC GEOGRAPHY AND

TECTONIC FEATURESTECTONIC FEATURES

%ndia lies at the north-westernend of the %ndo-Australian Plate#

whih enompasses %ndia#

Australia# a major portion of the%ndian /ean and other smaller

ountries.

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+AST EARTHQUAKES %$ %$D%A+AST EARTHQUAKES %$ %$D%A

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SEISMIC ZONES OFSEISMIC ZONES OF


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SEISMIC ZONES OFSEISMIC ZONES OF

INDIAINDIA &he varying geology at different loations in the ountry

implies that the likelihood of damaging earthquakes

taking plae at different loations is different.

&hus# a seismi @one map is required to identify these

regions.

Based on the levels of intensities sustained during

damaging past earthquakes# the +F version of the @onemap subdivided %ndia into five @ones %# %%# % %%# %= and

= .

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%ndian ;eismi Hone 0ap of +F06/12/16 4(


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&he seismi @one maps are revised from time to time as

more understanding is gained on the geology# the

seismotetonis and the seismi ativity in the ountry.

&he %ndian ;tandards provided the first seismi @one

map in +8,# whih was later revised in +8F and again

in +F.

&he map has been revised again in ,, and it now has

only four seismi @ones %%# %%%# % = and =.

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;eismi @onation and intensity map of %ndia06/12/16 #1


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World Largest Earthquake model test
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introduction of earthquake

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