elementry seiesmology

7/23/2019 elementry seiesmology

1/38

ELEMENTRYELEMENTRYSEISMOLOGYSEISMOLOGY


2/38

Earthquake occurrence in the worldEarthquake occurrence in the world


3/38

Platetectonic

s

Pla

tetectonics

The outermost portion o Earth isThe outermost portion o Earth is

composed o a mosaic o thin ri!id platescomposed o a mosaic o thin ri!id plates

pieces o lithospherepieces o lithosphere that mo"ethat mo"ehori#ontall$ with respect to one another%hori#ontall$ with respect to one another%

Plates interact with each other alon! theirPlates interact with each other alon! theired!es calleded!es called plate &oundaries%plate &oundaries%

Plate &oundaries ha"e a hi!h de!ree oPlate &oundaries ha"e a hi!h de!ree o

tectonic acti"it$ mountain &uildin!'tectonic acti"it$ mountain &uildin!'

earthquakes' acti"e "olcanoes%earthquakes' acti"e "olcanoes%


4/38

(hemical compositi(rustMantle(ore

Physical propertiLithosphereAsthenosphere

MesosphereOuter coreInner core


5/38


6/38

)

TYPES

)

TYPES

*I+ERGENT

(ON+ERGENT

TR,NS-ORM


7/38

, ault is nothin! &ut a crack or weak #one, ault is nothin! &ut a crack or weak #one

inside the Earth% .hen two &locks o rockinside the Earth% .hen two &locks o rock

or two plates ru& a!ainst each other alon!or two plates ru& a!ainst each other alon!a ault' the$ don/t 0ust slide smoothl$%a ault' the$ don/t 0ust slide smoothl$%

,s the tectonic orces continue to pre"ail',s the tectonic orces continue to pre"ail'

the plate mar!ins e1hi&it deormation asthe plate mar!ins e1hi&it deormation as

seen in terms o &endin!' compression'seen in terms o &endin!' compression'tension and riction% Thetension and riction% The rocks e"entuall$rocks e"entuall$

&reak !i"in! rise to an earthquake&reak !i"in! rise to an earthquake''

&ecause o &uildin! o stresses &e$ond the&ecause o &uildin! o stresses &e$ond the

limitin! elastic stren!th o the rock%limitin! elastic stren!th o the rock%

-aults22

%

-aults22

%


8/38


9/38


10/38


11/38


12/38

345 o land mass prone to earthquakes345 o land mass prone to earthquakes

67 million hectares 895: o landmass prone to67 million hectares 895: o landmass prone to

;oods;oods

9777 landslides>=ailstorms>cloud&urst

?95 o the total area suscepti&le to drou!ht?95 o the total area suscepti&le to drou!ht

*i@erent t$pes o manmade =a#ards*i@erent t$pes o manmade =a#ards

Tsunami threatTsunami threat

A million houses dama!ed annuall$ B human'A million houses dama!ed annuall$ B human'

economic' social and other losseseconomic' social and other losses

Earthquakeha#ardm

apoindiaC

states22%%

Earthquakeha#ardm

apoindiaC

states22%%


13/38

-i!% courtes$D nicee

More than ?7 5area isearthquakeprone%

one + F "er$hi!h

one I+ F hi!h

one IIIFmoderate

one II F low

Earthquakeha#ardm

apoindiaC

states22%%

Earthquakeha#ardm

apoindiaC

states22%%


14/38

Earthquakeha#ardm

apoindiaC

states22%%

Earthquakeha#ardm

apoindiaC

states22%%

*


15/38

An earthquake is theAn earthquake is the vibrationvibration

of Earthof Earth produced by theproduced by the rapidrapid

release of energyrelease of energy.. Energy radiates inEnergy radiates in all directionsall directions

from its source thefrom its source the focusfocus..

Energy moves likeEnergy moves like !aves!aves..

*eG

nition

22Earthquakes are caused bysudden release of energy inrocks.

Plates in the form of rocksare moving very slo!ly andearthquake occur !henmoving plates grind and scrape

against each other.

(auses2

2


16/38

Shakin! o earth due to mo"ement oShakin! o earth due to mo"ement o

rocks alon! a ault%rocks alon! a ault%

Rocks under stress accumulate strainRocks under stress accumulate strain

ener!$ o"er time%ener!$ o"er time%

.hen stress e1ceeds stren!th o.hen stress e1ceeds stren!th o

rocks' rock &reaks%rocks' rock &reaks% Strain ener!$ is released as seismicStrain ener!$ is released as seismic

wa"es% The lon!er that ener!$ iswa"es% The lon!er that ener!$ is

stored up and is maintained withoutstored up and is maintained without

release' the more likel$ that a stron!release' the more likel$ that a stron!

earthquake will occur%earthquake will occur%

prediction22

,


17/38

,nato

m$

o

earth

quake%%


18/38


19/38

-O(HS-O(HS the place within Earth where earthquake the place within Earth where earthquake

wa"es ori!inatewa"es ori!inate

EPI(ENTEREPI(ENTER

Point on the surace' directl$ a&o"e the ocus%Point on the surace' directl$ a&o"e the ocus%Located usin! the di@erence in the arri"al timesLocated usin! the di@erence in the arri"al times

&etween P and S wa"e recordin!s' which are&etween P and S wa"e recordin!s' which are

related to distance%related to distance%

-O(HS-O(HS

The distance &etween the ocus and the epicenter isThe distance &etween the ocus and the epicenter is

called ocal depth%called ocal depth%

*EPT= O- -O(HS

Shallow ocus EarthquakesFJ7 km deep

Intermediate ocus earthquakesFJ7 F )77km

*eep ocus earthquakes)77 km


20/38

TheThe ocusocuso an earthquake is the ori!in ato an earthquake is the ori!in at

depth o that earthquake% The closestdepth o that earthquake% The closest

place on the surace o the earth to theplace on the surace o the earth to the

ocus is called the epicenter%ocus is called the epicenter%

,n epicenter is located &$ trian!ulatin!,n epicenter is located &$ trian!ulatin!

&etween ) or more seismo!raph stations'&etween ) or more seismo!raph stations'usin! the arri"al times o two or more ousin! the arri"al times o two or more o

the ) t$pes o earthquake wa"es%the ) t$pes o earthquake wa"es%


21/38

The term KSeismolo!$/ is deri"ed rom

Greek word Seismo' which meansearthquakeand lo!os meansscience hence the Seismolo!$ isScience o Earthquakes

Seismolo!$ can &e dened in two wa$sDA% The science o earthquakes and the

ph$sics o the earth/s interior

% The science o elastic wa"e 8seismicwa"es:

s

eismolo!$22


22/38

Seismicw

a"es2

2

od$ .a"es-tra"el throu!h interiorPrimar$ !aves"PFwa"esHighest velocity Causes compression and expansion in direction of

wave travel.

SEISMI( .,+ESSEISMI( .,+ESproduced &$ the release o ener!$mo"e out in circles rom the point o rupturemo"e out in circles rom the point o rupture

8ocus:8ocus:
http://www.yenka.com/freecontent/attachment.action?quick=9x&att=706http://www.yenka.com/freecontent/attachment.action?quick=9x&att=706http://www.yenka.com/freecontent/attachment.action?quick=9x&att=706


23/38

SE(ON*,RY .,+ESF SF.,+ESSE(ON*,RY .,+ESF SF.,+ES

Slower than P waves but faster than surface waves.Slower than P waves but faster than surface waves.

Causes shearing of rock perpendicular to direction of wave propagationCauses shearing of rock perpendicular to direction of wave propagation

Cannot travel through liquidsCannot travel through liquids

Seismicw

a"es2

2


24/38

Surace .a"esSurace .a"es FFtra"el on suracetra"el on suraceo eartho earth

Cause vertical hori!ontal shaking.Cause vertical hori!ontal shaking.

"ravel exclusively along surface of earth."ravel exclusively along surface of earth.Lo"e wa"esLo"e wa"es

Ra$lei!h wa"esRa$lei!h wa"es

Seismicw

a"es2

2

Ra$lei!h wa"es' also called !round roll' are suracewa"es that are conned to the Earths suracewhere the$ tra"el as ripples with motions that aresimilar to those o wa"es on the surace o water%

The surace particles mo"e in ellipses in planes

normal to the surace and parallel to the directiono propa!ation% ,t the surace and at shallowdepths this motion is retro!rade 8unlike waterwa"es:% Particles deeper in the material mo"e insmaller ellipses with an eccentricit$ that chan!eswith depth%

L i i


25/38

Lo"e wa"es are surace seismicwa"es that cause hori#ontalshitin! o the earth durin! anearthquake% The particle motiono a Lo"e wa"e orms a

hori#ontal line perpendicular tothe direction o propa!ation 8i%e%are trans"erse wa"es:% Theamplitude' or ma1imum particlemotion' oten decreases rapidl$with depth%


26/38


27/38


28/38

Measurin! the si#e o earthquakesMeasurin! the si#e o earthquakes

T.O ME,SHREMENTS *ES(RIE T=E SIE O- ,NT.O ME,SHREMENTS *ES(RIE T=E SIE O- ,N

E,RT=H,


29/38

M,GNITH*EM,GNITH*E Estimates the amount o ener!$ Estimates the amount o ener!$

released &$ the earthquake%released &$ the earthquake%The ma!nitude o anThe ma!nitude o an

earthquake is determined instrumentall$ and is moreearthquake is determined instrumentall$ and is more

o&0ecti"e measure o its si#e%o&0ecti"e measure o its si#e%

'ichter magnitude'ichter magnitude" concept introduced by" concept introduced by

%harles 'ichter in ()*+%harles 'ichter in ()*+

'ichter scale'ichter scale

, -ased on amplitude of largest seismic !ave-ased on amplitude of largest seismic !ave

recordedrecorded, LOLO(/(/$%ALE$%ALE

, Each unit of 'ichter magnitude correspondsEach unit of 'ichter magnitude corresponds

to (/0 increase in !ave amplitude and *10to (/0 increase in !ave amplitude and *10

increase in Energy.increase in Energy.

Moment magnitudeMoment magnitude!as developed because!as developed because'ichter magnitude does not closely estimate'ichter magnitude does not closely estimatethe si2e of vey large earthquakes.the si2e of vey large earthquakes.

&erived from the amount of displacement that&erived from the amount of displacement thatoccurs along a fault and the area of the faultoccurs along a fault and the area of the faultthat slipsthat slips


30/38


31/38

(harcteristic o stron! !round motion(harcteristic o stron! !round motion Ground motion at a particular site due to earthquake is in;uenced &$ source' tr"elGround motion at a particular site due to earthquake is in;uenced &$ source' tr"el

path and local site condition% The rst relates to the si#e and source mechanism opath and local site condition% The rst relates to the si#e and source mechanism othe earthquake% The second descri&es the path e@ect o the earth as wa"es tra"el atthe earthquake% The second descri&es the path e@ect o the earth as wa"es tra"el at

some depth rom the source to the site% The third descri&es the e@ect o the uppersome depth rom the source to the site% The third descri&es the e@ect o the upper

hundreds o meters o rock and soil and the surace topo!raph$ at the site%stron!hundreds o meters o rock and soil and the surace topo!raph$ at the site%stron!

shakin! cause se"ere dama!es to manFmade acilities and unortunatel$' someshakin! cause se"ere dama!es to manFmade acilities and unortunatel$' some

times' induce losses o human li"es% Studies o the characteristics o o&ser"edtimes' induce losses o human li"es% Studies o the characteristics o o&ser"ed

accelero!rams rom earthquake e"ents up!rade ine's capa&ilit$ in seismic ha#ardaccelero!rams rom earthquake e"ents up!rade ine's capa&ilit$ in seismic ha#ard

miti!ation%miti!ation%

.a"e t$pe in"oled in stron! !round motion.a"e t$pe in"oled in stron! !round motion

hori#ontal !round motion is produced &$ s &od$ wa"es and &$ the surace wa"es%hori#ontal !round motion is produced &$ s &od$ wa"es and &$ the surace wa"es%

-actors that a@ect stron! !round motion-actors that a@ect stron! !round motion Ma!nitudeMa!nitude

*istance*istance

SiteSite -ault t$pe'depth and repeat time-ault t$pe'depth and repeat time

*irecti"it$ and radiation pattern*irecti"it$ and radiation pattern


32/38

, seismoLOGI(,L INSTRHMENTS, seismoLOGI(,L INSTRHMENTS

The heavy mass doesnt move much

The drum moves


33/38

In reality, copper wire coils move around magnets, generating current which is recorded.


34/38

3 ,mplitude o seismic wa"es 8how,mplitude o seismic wa"es 8how

much rock mo"es or "i&rates:much rock mo"es or "i&rates:

3 *istance to the epicenter*istance to the epicenter3 Earthquake directionEarthquake direction


35/38

, seismoscope is a scientic de"ice that si!nals the occurrence o, seismoscope is a scientic de"ice that si!nals the occurrence o

an earthquake' possi&l$ pro"idin! inormation a&out the timin! andan earthquake' possi&l$ pro"idin! inormation a&out the timin! and

si#e o the quake as well%si#e o the quake as well%It should not &e conused with aIt should not &e conused with a seismometerseismometer' a measurin!' a measurin!

instrument' or the closel$ relatedinstrument' or the closel$ related seismo!raphseismo!raph' which !enerates a' which !enerates arecord o the shakin!% Geolo!ists do not widel$ use seismoscopes'record o the shakin!% Geolo!ists do not widel$ use seismoscopes'&ecause the ran!e o data the$ can record is limited when&ecause the ran!e o data the$ can record is limited whencompared with more sophisticated equipment%compared with more sophisticated equipment%

O"er time' seismoscope technolo!$ &ecame more sophisticated%O"er time' seismoscope technolo!$ &ecame more sophisticated%

In"entors worked on de"ices capa&le o measurin! the intensit$ oIn"entors worked on de"ices capa&le o measurin! the intensit$ o

earthquakes so the$ could collect &etter data' and the$ alsoearthquakes so the$ could collect &etter data' and the$ also

de"eloped seismoscopes with timers to tell them when quakesde"eloped seismoscopes with timers to tell them when quakes

occurred% The de"elopment o the seismo!raph and seismometeroccurred% The de"elopment o the seismo!raph and seismometercontri&uted e"en more useul inormation earl$ de"ices used acontri&uted e"en more useul inormation earl$ de"ices used a

simple pendulumsimple pendulumattached to a st$lus to record an earthquake inattached to a st$lus to record an earthquake in

ull' allowin! people to track the intensit$ o the shakin! and look atull' allowin! people to track the intensit$ o the shakin! and look at

the pattern o mo"ement inside the EarthQs crust%the pattern o mo"ement inside the EarthQs crust%

seismoscope
http://www.wisegeek.com/what-is-a-seismometer.htmhttp://www.wisegeek.com/what-is-a-seismometer.htmhttp://www.wisegeek.com/what-is-a-seismograph.htmhttp://www.wisegeek.com/what-is-a-seismograph.htmhttp://www.wisegeek.com/what-is-a-simple-pendulum.htmhttp://www.wisegeek.com/what-is-a-simple-pendulum.htmhttp://www.wisegeek.com/what-is-a-simple-pendulum.htmhttp://www.wisegeek.com/what-is-a-seismograph.htmhttp://www.wisegeek.com/what-is-a-seismometer.htm


36/38

The seismoscope is useul primaril$ as an alert s$stem to let peopleThe seismoscope is useul primaril$ as an alert s$stem to let people

know an earthquake happened% More modern scientic equipmentknow an earthquake happened% More modern scientic equipment

pro"ides inormation a&out the details and does not 0ust si!nal to alertpro"ides inormation a&out the details and does not 0ust si!nal to alertpeople to the occurrence o a quake% $ usin! a network o equipmentpeople to the occurrence o a quake% $ usin! a network o equipment

to measure seismic acti"it$' researchers can pinpoint the epicenters oto measure seismic acti"it$' researchers can pinpoint the epicenters o

earthquakes' track earthquake acti"it$' and learn more a&out theearthquakes' track earthquake acti"it$' and learn more a&out the

ori!ins o quakes% These de"ices are also useul or acti"ities likeori!ins o quakes% These de"ices are also useul or acti"ities like

issuin!issuin! tsunamitsunamiwarnin!s%warnin!s%

It is possi&le to &uild a simple seismoscope at home' and directions canIt is possi&le to &uild a simple seismoscope at home' and directions can&e ound in scientic acti"it$ &ooks as well as online% One pro&lem with&e ound in scientic acti"it$ &ooks as well as online% One pro&lem with

this and other de"ices to measure earthquake acti"it$ is the de!ree othis and other de"ices to measure earthquake acti"it$ is the de!ree o

sensiti"it$% The machine ma$ issue a alse alarm or a passin! hea"$sensiti"it$% The machine ma$ issue a alse alarm or a passin! hea"$

truck' or ail to detect a "er$ distant quake &ecause the EarthQs motiontruck' or ail to detect a "er$ distant quake &ecause the EarthQs motion

is so su&tle% Researchers use tools like pro&es located underneath theis so su&tle% Researchers use tools like pro&es located underneath the

Earth to conrm that shakin! is caused &$ an earthquake and to collectEarth to conrm that shakin! is caused &$ an earthquake and to collectdata a&out the directionalit$ o the mo"ement%data a&out the directionalit$ o the mo"ement%

seismoscope
http://www.wisegeek.com/what-is-a-tsunami.htmhttp://www.wisegeek.com/what-is-a-tsunami.htmhttp://www.wisegeek.com/what-is-a-tsunami.htm


37/38

,n,n accelerographaccelerographcan &e reerred to as a stron! motioncan &e reerred to as a stron! motion seismo!raphseismo!raph''

or simpl$ as anor simpl$ as an earthquakeearthquakeaccelerometeraccelerometer% The$ are usuall$ constructed% The$ are usuall$ constructed

as a selFcontained &o1' more commonl$ now &ein! connected directl$ toas a selFcontained &o1' more commonl$ now &ein! connected directl$ to

thethe InternetInternet%%

,ccelero!raphs are useul or when the earthquake !round motion is so,ccelero!raphs are useul or when the earthquake !round motion is sostron! that it causes the more sensiti"e seismometers to !o o@Fscale%stron! that it causes the more sensiti"e seismometers to !o o@Fscale%

There is an entire science o stron! !round motion' that is dedicated toThere is an entire science o stron! !round motion' that is dedicated to

placin! accelero!raphs in the "icinit$ o ma0or aults% The t$pe oplacin! accelero!raphs in the "icinit$ o ma0or aults% The t$pe o

inormation !athered 8such as rupture "elocit$: would not &e possi&leinormation !athered 8such as rupture "elocit$: would not &e possi&le

with the standard seismometers% The &est known e1ample is thewith the standard seismometers% The &est known e1ample is the

Parkeld E1periment which in"ol"ed a massi"e set o stron! motionParkeld E1periment which in"ol"ed a massi"e set o stron! motioninstrumentation%instrumentation%RMSRMS

The$ record peak !round acceleration 8PG,:' "elocit$ 8PG+:' !roundThe$ record peak !round acceleration 8PG,:' "elocit$ 8PG+:' !round

displacement 8PG*: and spectral intensit$ 8SI:%displacement 8PG*: and spectral intensit$ 8SI:%

.ithin the accelero!raph' there is an arran!ement o ) accelerometer.ithin the accelero!raph' there is an arran!ement o ) accelerometer

sensin! heads% These are usuall$ microFmachined 8MEMS: chips that aresensin! heads% These are usuall$ microFmachined 8MEMS: chips that aresensiti"e to one direction% Thus constructed' the accelerometer cansensiti"e to one direction% Thus constructed' the accelerometer can

measure ull motion o the de"ice in three dimensions%measure ull motion o the de"ice in three dimensions%

accelero!raph
http://en.wikipedia.org/wiki/Seismographhttp://en.wikipedia.org/wiki/Seismographhttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Accelerometerhttp://en.wikipedia.org/wiki/Accelerometerhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Accelerometerhttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Seismograph


38/38

Hnlike the continuall$ recordin! seismometer'Hnlike the continuall$ recordin! seismometer'

accelerometers nearl$ alwa$s work in a tri!!ered mode%accelerometers nearl$ alwa$s work in a tri!!ered mode%

That means a le"el o acceleration must &e set which startsThat means a le"el o acceleration must &e set which starts

the recordin! process% This makes maintenance much morethe recordin! process% This makes maintenance much moredicult without a direct Internet connection 8or some otherdicult without a direct Internet connection 8or some other

means o communication:% Man$ trips ha"e &een made tomeans o communication:% Man$ trips ha"e &een made to

accelerometers ater a lar!e earthquake' onl$ to nd thataccelerometers ater a lar!e earthquake' onl$ to nd that

the memor$ was lled with e1traneous noise' or thethe memor$ was lled with e1traneous noise' or the

instrument was malunctionin!%instrument was malunctionin!% ,ccelerometers are used to monitor structures or,ccelerometers are used to monitor structures or

earthquake response% Sometimes' with the data' a responseearthquake response% Sometimes' with the data' a response

spectrum is computed% Other anal$sis is used to impro"espectrum is computed% Other anal$sis is used to impro"e

&uildin! desi!n' or to help locate important structures in&uildin! desi!n' or to help locate important structures in

saer areas%saer areas%

l h

elementry seiesmology

Documents