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ELEMENTRYELEMENTRYSEISMOLOGYSEISMOLOGY
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Earthquake occurrence in the worldEarthquake occurrence in the world
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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%
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(hemical compositi(rustMantle(ore
Physical propertiLithosphereAsthenosphere
MesosphereOuter coreInner core
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)
TYPES
)
TYPES
*I+ERGENT
(ON+ERGENT
TR,NS-ORM
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, 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
%
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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%%
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-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%%
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Earthquakeha#ardm
apoindiaC
states22%%
Earthquakeha#ardm
apoindiaC
states22%%
*
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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
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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
,
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,nato
m$
o
earth
quake%%
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-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
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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%
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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!$22
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Seismicw
a"es2
2
od$ .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!$mo"e out in circles rom the point o rupturemo"e out in circles rom the point o rupture
8ocus:8ocus:
http://www.yenka.com/freecontent/attachment.action?quick=9x&att=706http://www.yenka.com/freecontent/attachment.action?quick=9x&att=706http://www.yenka.com/freecontent/attachment.action?quick=9x&att=7067/23/2019 elementry seiesmology
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SE(ON*,RY .,+ESF SF.,+ESSE(ON*,RY .,+ESF SF.,+ES
Slower than P waves but faster than surface waves.Slower than P waves but faster than surface waves.
Causes shearing of rock perpendicular to direction of wave propagationCauses shearing of rock perpendicular to direction of wave propagation
Cannot travel through liquidsCannot travel through liquids
Seismicw
a"es2
2
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Surace .a"esSurace .a"es FFtra"el on suracetra"el on suraceo eartho earth
Cause vertical hori!ontal shaking.Cause vertical hori!ontal shaking.
"ravel exclusively along surface of earth."ravel exclusively along surface of earth.Lo"e wa"esLo"e wa"es
Ra$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
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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$with depth%
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Measurin! the si#e o earthquakesMeasurin! the si#e o earthquakes
T.O ME,SHREMENTS *ES(RIE T=E SIE O- ,NT.O ME,SHREMENTS *ES(RIE T=E SIE O- ,N
E,RT=H,
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M,GNITH*EM,GNITH*E Estimates the amount o ener!$ 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
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(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
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, seismoLOGI(,L INSTRHMENTS, seismoLOGI(,L INSTRHMENTS
The heavy mass doesnt move much
The drum moves
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In reality, copper wire coils move around magnets, generating current which is recorded.
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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
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, 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.htm7/23/2019 elementry seiesmology
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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.htm7/23/2019 elementry seiesmology
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,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/Seismograph7/23/2019 elementry seiesmology
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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