determining the epicentre location hampir fiiix.docx

7/25/2019 Determining The Epicentre Location hampir fiiix.docx

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PRACTICAL REPORT

DETERMINING THE EPICENTRE LOCATION

By :

Asri Maharani 14312241051

NATURAL SCIENCE EDUCATION STUDY PROGRAM

MATHEMATICS AND NATURAL SCIENCES FACULTY

YOGYAKARTA STATE UNIVERSITY

2015


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Determinin T!e E"i#entre L$#%ti$n

A& O'(e#ti)e* $+ T!e E,"eriment

Determine the epicenter location of an earthquake

-& H."$t!e*i*If the station istance to the epicentre is further! the time ifference of arri"al # an $

%a"e in that station is lon&er

C& T!e$r.

1& E%rt!/%e

Earthquakes occur within the Earths crust along faults that

suddenly release large amounts of energy that have built up over

long periods of time. The shaking during an earthquakeis caused by

seismic waves. Seismic wavesare generated when rock within the

crust breaks, producing a tremendous amount of energy. The energy

released moves out in all directions as waves, much like ripples

radiating outward when you drop a pebble in a pond. The Earths

crust near tectonic plate edges are forced to bend, compress, and

stretch due to theinternal forces within the earth, causing

earthquakes. Nearly all earthquakes occur at plate boundaries

!nnonym, "##$%.a. Seismic wave

Seismic waves are waves of energy that elastically distort the

material that they travel through. &ence, after a seismic wave has

passed through an elastic body of rock, it returns to its original

shape and volume. Seismic waves are generated by the release of

energy during an earthquake. They travel through the earth like

waves travel through water. Two types of seismic waves are

generated at the earthquake focus'1) Body waves spread outward from the focus in all directions.2) Surface waves spread outward from the epicenter to the

Earths surface, similar to ripples on a pond. These waves can

move rock particles in a rolling motion that very few structures

can withstand. These waves move slower than body waves.b. H."$#enter %n E"i#enter

The region of initiation of seismic energy within the Earth

during an earthquake is the focus or hypocenter (igure )%. Theposition on the land surface immediately above the hypocenter is


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the epicenter (igure )%. !s rupture along a fault initiates, waves

of energy travel outward from the hypocenter in a spherical

fashion. These waves of energy are strongest nearest the

hypocenter but gradually grow weaker further away from the siteof initial rupture *irty,"##+%.

Figure 2. Schematic illustration of location of epicenter and

hypocenter. Orange sphere is outward radiating seismic energy.

c. P and Swaves1) PWaves-!s the energy associated with -waves moves

outward in spherical fashion from the hypocenter it produces a

series of contractions and epansions in the direction that it is

traveling, i.e., in the wave propagation direction. /uring

contractions, the distances between atoms in the material that

the -wave is passing through shorten, and as a result thereis a

small decrease in volume. /uring epansions, the distances

between atoms in the material increase, and there is a small

increase in volume. (ollowing the complete passing of a -wave,

the elastically distorted Earth material returns to its original

volume. -waves can pass through liquids, solids, and gasses.2) SWaves. 0n contrast to -waves, S-waves emanating outward

in a spherical fashion from the focus produce shape rather than

volumetric changes in Earth material. 1hen an Swave passes

through the Earth it displaces particles in a direction

perpendicular to the direction. that it is moving, i.e., it2s

propagation direction. 3ecause liquids cannot support a shape

change, S-waves traveling through the interior of the Earth do


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not propagate through the liquid outer core and magma

chambers.d. Speeds of P and SWaves

Near the Earth2s surface in continental regions -waves can

travel at speeds around 4 km5sec while S-waves travel at speeds

around 6.$ km5sec. 3ecause -waves are faster than S-waves they

arrive at seismic stations earlier than S-waves. (or this reason

they are often referred to as primary waves while the slower

traveling S-waves, arriving a little later than the -waves at the

seismic station, are sometimes called secondary waves

*irty,"##+%e. Seismograph

! seismograph is the device used to record the vibrations

produced during an earthquake. The idea behind many

seismographs involves the concept of inertia. 7ur physics

colleagues tell us that inertia is the resistance a mass has to

sudden movement. 0n general, the greater the weight of an

ob8ect, the greater it will resist movement during an earthquake.

Seismologists are geologists that study earthquakes. They have

used the idea of inertia in their construction of so called 9inertial

seismographs:. 0n practice they suspend a dense heavy ob8ect

from a spring or wire. 3ecause of its great weight, the suspended

ob8ect has so much resistance to movement that when the spring

or wire it is attached to is suddenly etended during an

earthquake it does not move. !s shown in (igure ;, a pen

attached to the dense ob8ect is in contact with paper


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f. Earh!ua"e #agniudesThe amplitude of the squiggly curve of the seismogram

provides information about the energy released during an

earthquake. The =ichter magnitude is determined by the peak

amplitude on a seismogram derived from a 1ard-!nderson

seismometer, a special but ubiquitous type of seismometer. The

measured peak amplitude is scaled to a distance of )##

kilometers 4".) miles% from the epicenter of an earthquake. The

=ichter magnitude scale is logarithmic, with commonly reported

magnitudes varying from ) to a little over +. Each unit increase in

magnitude corresponds to a ten-fold increase in amplitude. (or

eample, a magnitude " earthquake produces a signal with an

amplitude that is ten times larger than a magnitude ) signal. !

magnitude 6 earthquake would produce a signal with an

amplitude one hundred times larger than a magnitude ) signal.

The modiercalli scale varies from I toXII, with higher

=oman numerals indicating greater intensity Table 6%. 0n general,

we would epect intensity to decrease outward away from theepicenter. &owever, over the last $# years or so buildings and

roads have been built under di?erent types of engineering codes,

and as a result such man-made structures have di?ering

resistance to ground shaking during an earthquake. &ence,

>ercalli intensities may vary from region to region and country to

country as a function of building code and other.


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2. $riangu%aionThere are many methods used for earthquake location.

Triangulation is a simple method, but fundamental in identifying

the necessary steps in any location procedure' identifying arrivals

and estimating the distance to the earthquake source. This is best

described by breaking the two words apart. =egional identi< es the

proimity of the earthquake to the station, speci< cally within )##

km to 4## km for this eercise. This allows us to use simpliorti@, "##$%


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0n earthquake location the time it takes for a seismic wave to

arrive at a given station can be broken into two partsA the time it

takes to travel hori@ontally and the time it takes to travel vertically.

3y only using earthquakes in close proimity to the station

regional )##B4##km% the waves do not penetrate deep into Earth

and we can ignore the vertical segment of the travel time and

focus on the hori@ontal segment.7ne method of


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9/21

oint

Station !, 3 and on the ma

Signed !, 3 and station on the paper. Start with sign the ".$ cm on the t

The location is the epicenter of the

E& Re*3t

T%'3e 1& C$n)ert Time t$ Di*t%n#e S#%3e

St%ti$n Time *e#$n6 Di*t%n#e m6 Di*t%n#e #m6

A

0 300 3

0 400 4

120 00

100 500 5

120 00

- 100 500 5

0 400 4

0 300 3

Step $ is repeated to station 3 and .


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120 00

100 500 5

C

0 400 4

100 500 5

0 400 4

0 400 40 300 3

T%'3e 2& T!e Di*t%n#e $+ E%rt!/%e E"i#entre

N$&Di*t%n#e +r$m t!e E%rt!/%e E"i#entre

A #m6 - #m6 C #m6

1& 2'5 4' 3'

2& 3 3 4'3

8& 6 6 69& 3'7 5'1 2'4

5& 6 6 6

F& An%3.*i*

#raktikum ini *ertu8uan untuk menentukan episentrum suatu &empa *umi' Alat an

*ahan yang digunakan adalah 8angka, penggaris, kertas &GS putih dan

alat tulis. Episentrum adalah pusat gempa bumi yang letaknya di

permukaan bumi sedangkan beragam metode yang digunakan untuk

menentukan 8arak episentrum diantaranya metoe lin&karan en&an ti&a

stasiun 9trian&ulation! metoe hiper*ola! metoe titik *erat! metoe &erak partikel! an

metoe ;ei&er'

#aa perco*aan ini metoe yan& i&unakan aalah metoe lin&karan en&an ti&a

stasiun' #roseur paa metoe penentuan episentrum en&an ti&a stasiun aalah

men&kon"ersikan 8arak episentrum paa keti&a stasiun ke alam satuan cm'


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St%*in A St%*in - St%*in C

Per'e%%n

4%t

%nt%r*t%*in *6

0 100 0

:%r%

e"i*entrm m6 300 500 400

$n)er*i r%i*

#m63 5 4

Berasarkan ata yan& iperoleh paa perco*aan pertama i atas! stasiun A memiliki

peru*ahan rentan& %aktu &elom*an& # an $ se*esar 0 s! stasiun B memliki peru*ahan

rentan& %aktu &elom*an& # an $ se*esar 100 s! an stasiun = memiliki peru*ahan

rentan& %aktu &elom*an& # an $ se*esar 0 s'

arak episentrum stasiun A se*esar 300 km! 8arak episentrum stasiun B se*esar 500

km! an 8arak episentrum stasiun = se*esar 400 km' -ilai terse*ut kemuian

ikon"ersikan setiap satuan 8arak yaitu setiap 1 cm me%akili 100 km' Dari kon"ersi

terse*ut iperoleh *ah%a stasiun A memiliki 8arak episentrum se*esar 3 cm! stasiun B

8arak episentrum se*esar 5 cm! an stasiun = 8arak episentrum se*esar 4 cm'

ari68ari lin&karan 9raius i*entuk *erasarkan 8arak episentrum yan& telah

ikon"ersikan ke alam satuan cm' #usat lin&karan merupakan titik stasiun' $etelah

lin&karan i&am*ar i setiap stasiun *erasarkan 8arak episentrum yan& iapatkan!

itemukan titik imana keti&a lin&karan *erpoton&an'

$etelah titik poton& lin&karan iapatkan! kemuian titik episentrum itentukan

en&an mem*entuk se&iti&a paa perpoton&an ti&a lin&karan terse*ut an menentukan

titik *eratnya' $etelah titik *erat se&iti&a terse*ut itemukan! maka praktikan

men&hu*un&kan titik terse*ut ke stasiun A! stasiun B! an stasiun =' (itik yan&

ihu*un&kan paa titik poton& merupakan 8arak stasiun ke pusat episentrum' Dari &am*ar

apat iketahui *ah%a stasiun A memiliki 8arak en&an pusat &empa se*esar 2'5 cm! 8arak

stasiun B en&an pusat &empa se*esar 4' cm an paa 8arak stasiun = en&an pusat

&empa se*esar 3' cm' >asilnya aalah se*a&ai *erikut:


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Gambar Sketsa Percobaan Pertama

Sumber : Dokumentasi pribadi

Dari hasil terse*ut! maka apat iketahui 8ika alam peta ukuran 1 cm sama en&an

100 km! maka 8arak sesun&&uhnya antara titik pusat &empa en&an masin&6masin& stasiun

aalah stasiun A 250 km! stasiun B 40 km an stasiun = aalah 30 km'

2& Per#$'%%n Ke72

(a*el Data #erco*aan 2


Per'e%%n

4%t

%nt%r*t%*in *6

0 0 100

:%r%

e"i*entrm m6400 400 500

$n)er*i r%i*

#m64 4 5



rentan& %aktu &elom*an& # an $ se*esar 0 s! an stasiun = memiliki peru*ahan rentan&

%aktu &elom*an& # an $ se*esar 100 s'




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apat iketahui *ah%a stasiun A memiliki 8arak en&an pusat &empa se*esar 3 cm! 8arak

stasiun B en&an pusat &empa se*esar 3 cm an paa 8arak stasiun = en&an pusat &empa

se*esar 3 cm' >asilnya aalah se*a&ai *erikut:

'

Gambar Sketsa Percobaan kedua




aalah stasiun A 300 km! stasiun B 300 km an stasiun = aalah 430 cm'

8& Per#$'%%n Ke78


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Per'e%%n

4%t

%nt%r*t%*in *6

120 0 0

:%r%

e"i*entrm m600 300 400

$n)er*i r%i*

#m6 3 4



rentan& %aktu &elom*an& # an $ se*esar 0 s! an stasiun = memiliki peru*ahan rentan&

%aktu &elom*an& # an $ se*esar 0 s'arak episentrum stasiun A se*esar 00 km! 8arak episentrum stasiun B se*esar 300



terse*ut iperoleh *ah%a stasiun A memiliki 8arak episentrum se*esar cm! stasiun B










ihu*un&kan paa titik poton& merupakan 8arak stasiun ke pusat episentrum' #aa &am*ar

tiak itemukan &aris sin&in& antara keti&a lin&karan'


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Gambar Sketsa Percobaan ketiga


(iak itemukannya titik sin&un& ari keti&a lin&karan ini imun&kinkan karena

&etaran yan& irasakan pen&amat san&at lemah atau memiliki skala intensitas moifie

mercalli no' I! *aik paa 8enis &elom*an& primer! &elom*an& sekuer! maupun &elom*an&

pan8an&' $ehin&&a &etaran yan& san&at lemah ini! tiak mampu men8an&kau &elom*an&

yan& *erasal ari aerah pen&amat lain' Di sampin& itu! faktor lain penye*a* tiak

itemukannya &aris sin&&un& lin&karan karena metoe lin&karan en&an ti&a stasiun inimem*utuhkan tin&kat akurasi yan& tin&&i sehin&&a pem*uatan lin&karan harus ilakukan

secara *erulan&6ulan&'

9& Per#$'%%n Ke79



Per'e%%n

4%t

%nt%r*t%*in *6

100 120 0

:%r%

e"i*entrm m6500 00 400

$n)er*i r%i*

#m65 4






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8arak episentrum se*esar cm! an stasiun = 8arak episentrum se*esar 4 cm'










apat iketahui *ah%a stasiun A memiliki 8arak en&an pusat &empa se*esar 3!7 cm! 8arak

stasiun B en&an pusat &empa se*esar 5!1 cm an paa 8arak stasiun = en&an pusat

&empa se*esar 2!4 cm' >asilnya aalah se*a&ai *erikut:

;am*ar $ketsa #erco*aan keempat

$um*er : Dokumentasi pri*ai



aalah stasiun A 370 km! stasiun B 510 km an stasiun = aalah 240 km'


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5& Per#$'%%n Ke75



Per'e%%n

4%t%nt%r*t%*in *6

120 100 0

:%r%

e"i*entrm m600 500 300

$n)er*i r%i*

#m6 5 3








terse*ut iperoleh *ah%a stasiun A memiliki 8arak episentrum se*esar cm! stasiun B


ari68ari lin&karan 9raius i*entuk *erasarkan 8arak episentrum yan& telahikon"ersikan ke alam satuan cm' #usat lin&karan merupakan titik stasiun' $etelah







ihu*un&kan paa titik poton& merupakan 8arak stasiun ke pusat episentrum' #aa &am*ar

tiak itemukan &aris sin&un& antara keti&a lin&karan'


18/21

Gambar Sketsa Percobaan kelima


(iak itemukannya titik sin&un& ari keti&a lin&karan ini imun&kinkan karena

&etaran yan& irasakan pen&amat san&at lemah atau memiliki skala intensitas moifie

mercalli no' I! *aik paa 8enis &elom*an& primer! &elom*an& sekuer! maupun &elom*an&

pan8an&' $ehin&&a &etaran yan& san&at lemah ini! tiak mampu men8an&kau &elom*an&

yan& *erasal ari aerah pen&amat lain' Di sampin& itu! faktor lain penye*a* tiak

itemukannya &aris sin&&un& lin&karan karena metoe lin&karan en&an ti&a stasiun ini

mem*utuhkan tin&kat akurasi yan& tin&&i sehin&&a pem*uatan lin&karan harus ilakukan

secara *erulan&6ulan&'

Ke*im"3%n

Berasarkan perco*aan an hasil pem*ahasan yan& telah ilakukan! maka

apat isimpulkan *ah%a episentrum &empa paa perco*aan itentukan en&an

metoe lin&karan en&an ti&a stasiun iapatkan titik episentrum yan& *erupa titik

perpoton&an antara keti&a lin&karan en&an 8arak episentrum ari stasiun iukur ari

titik perpoton&an 9episentrum' Dalam perco*aan ini maka iapatkan episentrum

&empa yan& itemukan aalah:

a' #aa perco*aan pertama yaitu 8arak pusat episentrum ari stasiun A aalah 2'5 cm

8ika ikon"ersi ke alam km setara 250 km! ari stasiun B aalah 4' cm atau 40

km ! an 8arak ari stasiun = aalah 3' cm atau sama en&an 30 km'

*' #aa perco*aan keua 8arak pusat episentrum ari stasiun A aalah 3 cm 8ika

ikon"ersi ke alam km setara 300 km! ari stasiun B aalah 3 cm atau 300 km !

an 8arak ari stasiun = aalah 4!3 cm atau sama en&an 430 km'


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c' #aa perco*aan keti&a tiak iapatkan perpoton&an antara keti&a lin&karan

sehin&&a tiak iketahui 8arak episentrum ari lin&karan'

' #aa perco*aan keempat 8arak pusat episentrum ari stasiun A aalah 3!7 cm 8ika

ikon"ersi ke alam km setara 370 km! ari stasiun B aalah 5!1 cm atau 510 km !

an 8arak ari stasiun = aalah 2!4 cm atau sama en&an 240 km'

e' #aa perco*aan kelima tiak iapatkan perpoton&an antara keti&a lin&karan

sehin&&a tiak iketahui 8arak episentrum ari lin&karan'

G& C$n#3*i$n

Base on the e?periment an the results of the analysis that has *een one! it can *e

conclue that the epicenter of the earthquake on e?periments etermine usin& the

trian&ulation metho of points o*taine in the form of a thir point of intersection *et%een

the circle %ith the epicenter istance from the station measure from the point of

intersection 9epicenter' In this e?periment! the epicenter foun are:a' In the first e?periment is the istance from the epicenter center A station is 2'5 cm if

con"erte into km equi"alent to 250 km! from the station B is 4' cm or 40 km! an

the istance from the station = is 3' cm or equal to 30 km'

*' In a secon e?periment center istance of the epicenter from station A is 3 cm if

con"erte into km equi"alent to 300 km! from the station B is 3 cm or 300 km! an

the istance from the station = is 4'3 cm or equal to 430 km'

c' In the thir e?periment is not o*taine intersection of the three circles so it is not

kno%n %ithin the epicenter of the circle'' In the fourth trial center istance of the epicenter from station A is 3'7 cm if con"erte

into km equi"alent of 370 km! from the station B is 5'1 cm or 510 km! an the

istance from the station = is 2'4 cm or equal to 240 km !

e' In the fifth e?periment is not o*taine intersection of the three circles so it is not

kno%n %ithin the epicenter of the circle'

H& Re+eren#e

Annoynim'2005'Earthquake and Seismic Waves.=arolina: Department of ucation

;irty ;'>' 2007' Perilous Earth: Understanding Processes Behind atural Disasters.

=alifornia: Department of ;eolo&ical $ciences! $an Die&o'

Mc;eary! D'! #lummer! ='='! an =arlson! D'>' 2001'Ph!sical Geolog!. -e% .ork: Mc

;ra% >ill

/ri@! !nne >."##$.Earthquake Location !egional "riangulation with !eal

#ata.New >eico' Science Education Solutions

I& :%4%'%n Pert%n.%%n


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1'


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determining the epicentre location hampir fiiix.docx

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