Jurnal (Studi Kasus)

8/18/2019 Jurnal (Studi Kasus)

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POSITRON, Vol. I, No. 1 (2011), Hal. ISSN : 2301-

25

Pendugaan Struktur Patahan Dengan MetodeGayaberat

IbrahiSo!a")

")Pro#i $i%i&a $'IPN*'

Abstrak

T+lah #ila&&a ++li!ia !+!a/ +#/aa %!r&!r a!aha +//a&a+!o#+ /aab+ra!. o!ra% #+%i!a% !+r%+b! b+ra%o%ia%i #+/a &+!+bala %+#i+#a &+b+ra#aa %!r&!r a!aha a!a lia!a. !& +/+!ahi lo&a%i a!aha #alia!a a&a aoali r+%i#al !+rl+bih #ahl #ii%ah&a #ari aoali !o!al (anomaliBouguer ) #+/a +!o#+ +ra!a-ra!aa b+r/+ra&. o!r aoali r+%i#al++rliha!&a &+b+ra#aa lia!a #a a!aha %+ara &ali!a!i %+#a/&ai!+rr+!a%i &a!i!a!i3 #+/a +o#+la &+#+a 2 ++rliha!&a %+ara +la%lo&a%i a!aha. ari ha%il ++li!ia #i+rol+h bah6a lo&a%i a!aha%+%ar ai& b+ra#a#i ba/ia !irla! a/ b+rori+!a%i bara!la!- !+//ara %+#a/&a a!aha%+%aroral !+r%+bar %+ara lo&al a/ /a b+rori+!a%i bara!la!- !+//ara.

Kata Kunci: Patahan,ga y aberat

1.PendahuluanPa!aha a!a %+%ar a#alah b+r/+%+raba!a a/ a!ah #ari o%i%i %+la.+b+ra#aa a!aha #i %a! %i%i bi%ab+rilai +&ooi% a/ !i//i &ar+a

#aa! b+ra%o%ia%i #+/a +ra/&ahi#ro&arbo a!a +a#i alr &+laraa/a &+ +r&aa a/ +ba6ai+ral-i+ral b+rilai +&ooi% !i//i.Na, #i %i%i lai bi%a +#a!a/&a&+r/ia a/ #ia&iba!&a ol+hb+r/+%+ra a!aha %+hi//a +l!!+ra#ia /+a !+&!oi& a/ !i#a& ara/ ++la &orba i6a, a!+ri #a!aah lo/%or. Ol+ha i!, +#/aa&+b+ra#aa %!r&!r a!aha #a 8oa alr a!aha #i %a! #a+rah a!a6ilaah %a/a! +!i/.

Tb&a a!ara l++/ 'i&ro S#a#iaa la Sa!+ra b+ra#a a#ai//ira l++/ !+r%+b! #+/al++/ Sa#+ra Hi#ia,+/a&iba!&a !+ra#ia +aa%+2ara iri/ (oblique). P+aa ii+/ha%il&a ra/&aia a!aha%+%ar/+%+r +#a!ar (str ike slip fault ) b+rarahbara!la! !+//ara a/ %+aar#+/a la Sa!+ra (Hail!o,199). P+aa ii /a+/ha%il&a +/a/&a!a ;&i!

;ari%a a&iba! +r/+%+ra a!aha%+%ar#i %+aa/ b&i! ;ari%a(Sia#!a&, T.O, 2004).

Sa!+ra S+la!a #+/a ib &o!aPal+ba/ %+ba/ai ba/ia #ari laSa!+ra /a !i#a& l! #ari +/arh!b&a l++/ 'i&ro S#a #+/al++/ Sa#+ra Hi#ia. *+!a&

Sa!+ra S+la!a a/ %+&ara/b+ra#a #i ba/ia !ir la Sa!+ra+a#i hal a/ +ari& !& #i&ai.Hal ii #i%+bab&a &ar+a 6ilaah!+r%+b!, %aa! ii b+ra#a a#a o%i%i #ib+la/&a/ b%r #ari alr !+&!oi& a&!i #i ba/ia bara! la Sa!+ra(Ha#ia#oo,


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POSITRON, Vol. I, No. 1 (2011), Hal. ISSN : 2301-

26

#&&., 2007). Po%i%i ii +a#i&aSa!+raS+la!a %a/a! +ari& !&#i!+li!i.

!& +/+!ahi 8oa a!aha%+%ar #iSa!+ra S+la!a a&a +rl #ila&&a++li!ia a/ b+r&i%iab/a. Salah

%a! ++li!ia a/ +rl #ila&&a!& ++!&a 8oa a!aha #i6ilaah Sa!+ra S+la!a a#alah++li!ia /+o


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b

R

2

A(?,,8) %++r!i a#a Babar 1#ia!a&a #+/a +r%aaa :

4. Perhitungan !ek Gayaberat"enda Dua

Di#ensi

F ( r ) = G

mm

o

r ̂ r2

(1)C+& /aab+ra! b+#a #a #i+%ia#alah #a%ar +o#+la b+#ab+rb+!& =+r!i&al i!a. Da/ #ia&%#

b+#a 2-#i+%i a#alah b+#a 3-

&+!+ra/a :F E /aa a#a m , moG E &o%!a!a /aab+ra! (>,>7? 10 -11

N2/2)r E Fara& a!ara m #a mo E G

(?-?@)2(0- @)2(8-8@)2172

#i+%i a/ +ai+aa/ a/ %aa #i aa %aa%+aa/ !a& b+rhi//a a#a %alah %a!&oor#ia!. Pa#a /abar 3, ;JC$a#alah !i!i& %#! %+bah oli/o #a Pa#alah !i!i& aa! !+a! ++&/aab+ra! oli/o ii a&a #i!+!&a.P #ia//a %+ba/ai !i!i& %a! %i%!+&oor#ia! KL, #a oli/o b+ra#a a#abi#a/ KL. Sb L a#alah o%i!i &+ba6ah #a

θ a#alah o%i%i!i #ari arah %b Ko%i!i &+m r P(x’,y’,z’)

Q(x,y,z)

mo

%b L o%i!i. Hbb+r! (1949)+&&a bah6a &oo+ =+r!i&al++& /aab+ra! b+#a #a #i+%i a#a!i!i& P a#alah :

Babar 1. Baab+ra! a!ara #a !i!i&a%%a m

#a mo

P+r+a!a /aab+ra! #ari a%%a ma#a !i!i& A

a/ b+rara& r a#alah :

g = 2G∆ ρ ∫ zd θ

Pa

Q

(5)

X

g ( r )

= −Gm

r ̂r

2

θ ф

(2)R

B Z

r a#alah i! =+&!or a%%a a/ +/arah #ari ACm &+ mo./ a#alah +r+a!a /aab+ra! a/ #i#+ri!aa%%a mo ol+h a%%a m. F

D;ila a%%a m a#alah a%%a bi Me #a mo

a#alah b+#a #i +r&aa bi a&aZ E+r+a!a /aab+ra! a/ #ialai

b+#a moa#alah:

Ba ar 3. Cl++ /+o+!ri a/#iliba!&a #ala +rhi!/a++& /aab+ra!

g ( r ) = −G

M e

r ̂e

(3) oli/o b+r%i%i (Tal6ai, 1959)

Nilai +r+a!a /aab+ra! g #i+r&aa bi a#alah 90 %2.S+ba/ai +/hora!a &+a#a Balil+o,a&a %a!a +r2+a!a /aab+ra!

a#alah Balil+o (Bal) a/ %+!ara#+/a 1 2%2.

$. PotensialGayaberat

I!+/ral /ari% ii #ila&&a a#a%+lrh %i%ioli/o. S+ara +r%aaa iia#alah(T+lor#, 1990)

z i= a

isi φ

i!osφ

i


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θ i − θ i +" + #a φ i (>)'+#a /aab+ra! b+r%ia! &o%+r=a!i

bila %aha !& +//+ra&a %a!ar!i&+l #ala +#a !+r%+b! !i#a&!+r/a!/ a#a li!a%a a/ #ilali,!+!ai haa b+r/a!/ a#a !i!i& a6al#a !i!i& a&hir. Baab+ra! +ra&a

=+&!or a/ araha %+aa//ari% a/

$

! o

s θ i ( # a θ i− #a φ i )

!osθ i +" ( #aθ i +" − #a φ i )

+/hb/&a %a! &+#a a%%a.Baa ii +ibl&a +#a&o%+r=a!i a/ #aa! #ia!a&a%+ba/ai /ra#i+! #ari o!+%ial %&alar(?,,8) :

%.MetodologiP++!aa aoali r+%i#al #i/a&a#ala +o#+l&a +aa/ +!aaoali !& +/+!ahi++bara raa! a%%a ba!aa/ +//abar&a &oi/ra%i%!r&!r

∇U ( x, y, z ) = − F ( x, y,

z)

m

= − g ( x, y, z )

(4)

ba6ah +r&aa. !& ++r&a!aali%i% #a i!+rr+!a%i, ++li!ia ii+/abil r++r+%i #a!a-#a!a /+olo/i

#a ++li!ia !+r&ai! a!a ++li!ia#i %+&i!ar lo&a%i ++li!ia.


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2

#a la/&ah-la/&ah a/#ila&&a a#a ++li!ia ii a#alah:

1. or+&%i a%a/-%r!, #ri!,;o/+r #a #ara b+ba%.

2. '+i%ah&a aoalir+/ioal #a

r+%i#al +//a&a+ra!a-ra!aa b+r/+ra&.

3. '+o#+l&a ba6ah+r&aa 2

#+/a /+o+!ri oli/ob+r%i%i N.

4. I!+rr+!a%i b+r#a%ar&ao#+l or6ar# 2.

3) Penentuan apat Massa

Pa#a ++li!ia ii raa! a%a#i+%!ia%i #+/a +//a&a+!o#a N+!l+!o. C%!ia%i raa!a%%a !+rbai& a#a +!o#a ii

#i#aa! #ari &or+la%i %ila/!+r&+il (+#+&a!i ol) a!ara+rbaha +l+=a%i !+rha#aaoali /aab+ra!. P+r%aaaa/ #i/a&a a#alah %+ba/aib+ri&!:

N

∑ δ ( ∆ g ) iδ hik = i = " (9)

%.1. PengolahanDatao%+ aoali /aab+ra! ++&a&a

a#a a%+& +rb+#aa /aab+ra!!+r&r #+/a ilai /aab+ra! aa!& o#+l !+ori!i% bi (%h+roi#).P+rb+#aa !+r%+b! +r+3 l+&%i&a=aria%i raa! a%%a a/ !+r#aa! a#a%a! #a+rah #+/a %+&i!ara bai&hori%o!al a!a =+r!i&al. ;+%ar&+ila &+#alaa, arah aoaliraa! a%%a #i#aa!&a #+/a+/hi!/, +r+&o%!r&%i #ai!+rr+!a%i o#+l /aab+ra! !+r&r.Har/a /aab+ra! !+r&r +ra&a!o!al /aa +r+a!a a/ #i#+ri!a ol+h

%a! !i!i& a&iba! b+rba/ai %b+r.;+b+raa %b+r a/ ++/arhi+/&ra a#alah:

• Po%i%i bi #ala+r/+ra&a !a!a %ra (ti!ee"ect )

• P+rb+#aa li!a/ #i+r&aabi

• P+rb+#aa &+!i//ia +r&aabi

(+l+=a%i)

• C+& !oo/ra3i

• P+rbaha raa! a%%a #i%a!!+a! !& +/hi#ari ++&/aab+ra! #ari &oo+ a/!i#a& #i&+h+#a&i, a&a #ila&&a&or+&%i #a r+#&%i. Tahaa +/olaha #a!a %+ba/aib+ri&!:

#) Menghitung nilai gobser$asi+ra&a har/a /aab+ra!+/&ra a/ !+lah #i&or+&%i#+/a &or+&%i a%a/ %r! #a&or+&%i #ri! (a/a) ala!.

Nilai &or+&%i ii #i#+


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7/11

'. (asil Dan)nterpretasi'.1. Ano#ali "ouguerU

P+!a ii ++rliha!&a ola &o!rb+rori+!a%i bara!la!-!+//ara #+/a

ilai aoali bo/+r a!ara 37 hi//a59 Bal. Ori+!a%i &o!r a#a +!aii b+ra%o%ia%i #+/a arah !aa%!r&!r %+%ar ai! arah bara!la!-!+//ara. Nilai aoali r+#ahb+ra%o%ia%i #+/a ilai &o!ra% raa!a%%a ba!a a/ &+il %+#a/&a ilaiaoali !i//i b+ra%o%ia%i #+/a ilai

Babar 5. P+!a aoali r+%i#al+!+ra/a: S+%ar ai&

S+%ar !r

Babar 4. P+!a aoali

;o/+r

&o!ra% raa! a%%a ba!a a/ !i//i.P+rbaha ilai aoali r+#ah &+ !i//ia/ %a/a! %i/i


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aoali o%i!i #a +/a!i a #i#oi%ai ol+h ilaio%i!i. P+rbaha ilai aoali#ari o%i!i &+ +/a!i a/%i/i


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#+/a +rbaha ilai aoalio%i!i &+ +/a!i a/ !+ra#i a#a%+%ar ai& %++r!i a/ !+rliha! #i/ !irla! +aa/ li!a%a;. S+lai i!, &+#alaa ba!a#a%ar /a %a/a! ++/arhi

ilai aoali #i lo&a%i !+r%+b!.S+a&i #a/&al ba!a #a%ar #ilo&a%i !+r%+b! a&a ilai aoalia+#r/ o%i!i, %+bali&a i&a&+#alaa ba!a #a%ar #i lo&a%i!+r%+b! #ala a&a ilaiaoalia 2+#r/ +/a!i.+#alaa ba!a /rai! %+ba/aiba!a #a%ar a#a +aa/ iib+r&i%ar100 hi//a 325 #+/a ilai&o!ra% #+%i!a% M E 0.2> /3.;a!a %+#i+ a/ !+r+&a a#a

+aa/ ii #+/a ilai &o!ra%#+%i!a% b+r&i%ar -0.45 /23 hi//a0.25 /3. S+#a/&a ilai &o!ra%#+%i!a% lai%a la& a/+!ia b+r&i%ar -0.>0 /23.

• Pena#pang Geologi *intasan A" ;a!a Brai! #+/a &o!ra%#+%i!a%

0.2> /3 (Babar >). ;a!a ii!+r%i/&a a#a &+#alaa !o%+&i!ar100 300 #a !+r%+bar%+aa/ +aa/ a/+ra&a ba!a #a%ar.

;a!a%ir /ai/a#i%i%ii ba!%+rih #a&o/lo+ra! #+/a &o!ra%#+%i!a% 0.25 /3 ++a!iba/ia !+/ah +aa/#a b+r#a%ar&a +aa/+ili&i &+!+bala %+&i!ar >0 100.

;a!a%ir %+riha #i%i%ii

laa #+/a #+%i!a% 0.10/23. ;+r#a%ar&a +aa/+ili&i &+!+bala %+&i!ar >0 0 #a !+r%+bar%+aa/ +aa/.

;a!laa %+riha #i%i%iiba!a%ir #+/a &o!ra% #+%i!a%-0.35 /23. ;a!a iib+r#a%ar&a +aa/ +ili&i&+!+bala %+&i!ar >0 150 #a!+r%+bar #+/a bai& #i ba/iabara!#aa #a !irla!%+#a/&a #i ba/ia !+/ah+aa/ +/hila/ &ar+a

+/alai +ro%i. P+r%+li/a ba!l+/

#+/a %+rih #a ba!laa

b+r%i%ia ba!a%ir a/+ai &o!ra% #+%i!a%-0.45 /3. ;a!a iib+r#a%ar&a +aa/ +ili&i&+!+bala 150 #a ++a!iba/ia !irla!.

C#aa Ra6a #+/a #+%i!a%-0.>0 /3 +ra&a ha%il+la&a, %+#i+!a%i %/ai,a!ai, #a #+l!a a/ a%ih a&!i hi//a %+&ara/. S+#i+ ii+ili&i &+!+bala hi//a


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lha +!+r a/ +!i+r&aa %+aa/+aa/.

• StrukturGeologi

S!r&!r /+olo/i a/a#a a#a

+aa/ a#alaha!aha%+%ar !r, %+%ar ai&#a lia!a. S!r&!r ii#i%+bab&a /rai! %+ba/ai ba!a#a%ar ++robo% ba!a %+#i+#i a!a%a %+hi//a++bab&a !+ra#ia a!aha#a lia!a. S+%ar a/ a#a #iba/ia bara!#aa +aa/a#alah %+%ar !r, #i ba/ia!irla! %+%ar !r #a %+%arai&. Pa!aha%+%ar ai& %+arah#+/a %+%ar !aa Sa!+raai! arah bara!la!-!+//ara #iba/ia !irla! lo&a%i ++li!ia,a/ +ba!a%i aoali !i//i#a r+#ah. +b+ra#aaa!aha%+%ar !r a/ b+r%ia!lo2al +ra&a #aa&%+&#+r #ari %+%ar !aa.*ia!a !+ra#i #i ba/iabara!#aa #a !+/ah+aa/ a#a ba!a%+#i+.

Babar >. P+aa/ B+olo/i *i!a%a;

+. Kesi#pulan Dan Saran+.1. Kesi#pulan

1. Pa!aha a/ !+r#+!+&%i a#alaha!aha ai& #a a!aha !r.Pa!aha ai& b+ra#a #i ba/ia

!irla! %+#a/&a a!aha !r!+r%+bar %+ara lo&al. Ori+!a%i&+#a a!aha !+r%+b! a#alah

bara!la!-!+//ara,2. ;a!a #a%ar a#alah ba!a /rai!

a/ ++robo% ba!a %+#i+ #ia!a%a %+hi//a ++bab&a!+ra#ia a!aha #a lia!a.


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+.2. Saran!& +#aa!&a ha%il a/

l+bih a&ra! #a ++lrh, +rl#ila&&a +/&ra +!o#+ /+o

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