geologi dasar - 4

8/11/2019 Geologi Dasar - 4

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Major earthquakes dramatically demonstrate

that the earth is a dynamic, changing system.

Earthquakes, in general, represent a release of

built-up stress in the lithosphere. They occuralong faults, planar breaks in rock along which

there is displacement of one side relative to

the other.
http://localhost/var/www/apps/conversion/tmp/scratch_4/video%204/How%20Earthquakes%20Work_1.flv


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Elastic deformation of

common materials. A.

An elastically deformed

material, such as a bent

metal ruler, will springback to its original

shape B when released.

If the material is pushed

beyond the limits of its

strength, it may break

C, but the two halves

will each snap back to

their original shape

(straight, in the case ofthe ruler). This is an

analogy for the elastic

rebound theory of the

origin of earthquakes.

PLATE TECTONICS

AND EARTHQUAKE


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Seismic body waves: P and S

A.P wave alternately compresses and expands the rock as

the wave passes through. These squares illustrate thealternating compression and expansion. As waves pass

through, a square will repeatedly expand to a long

rectangle, return to a square, contract to a short,

squashed-looking rectangle, and so on.

B.S waves cause a shearing motion, like that of a rope

being shaken up and down. In this case, as the waves

pass through, the squares move up and down

perpendicular to the direction of S-wave travel. The

square doesn't expand or contract but changes itsshape, starting as a square, then becoming a distorted

parallelogram, and then changing back to a square


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P-Wave refraction and S-Wave Shadow Zone. P waves

are strongly bent (refracted) when they encounter the

boundary between the mantle and the core.


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Seismogram of a typical earthquake

This typical seismogram

illustrates the different travel

times for P waves, S waves,

and surface waves. The P

waves and S waves leave the

point of origin (the focus) at

the same instant. The faster-moving P waves reach the

seismograph first, followed

some time later by the

slower-moving S waves. The

surface waves, which travel

the long way around on theEarth's surface, arrive even

later.
http://localhost/var/www/apps/conversion/tmp/scratch_4/video%204/Seismik_3.flv


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The focus of an

earthquake is the actual

site of first movement

along a fault and the center

of energy release, which

usually occurs at somedepth.

The epicenter is the point

on the Earth's surface

directly above the focus; it

is used to specify the map

location of an earthquake.

FOCUS (HYPOCENTER)

AND

EPICENTER


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EARTHQUAKE AT

PLATE BOUNDARIES


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LETUSANGUNUNGAPI

GEMPABUMI


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RICHTER MAGNITUDE SCALE

Description Magnitude App. Energyreleased (ergs)

Great earthquake Over 8 Over 5.8 x 1023

Major earthquake 7 7.9 2 - 42 x 1022

Destructive earthquake 6 6.9 8 - 150 x 1020

Damaging earthquake 5 5.9 3 - 55 x 1019

Minor earthquake 4 4.9 1 - 20 x 1018

Smallest usually felt 3 3.9 4 - 72 x 1016

Detected but not felt 2 2.9 1 - 26 x 1015


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Modified Mercalli Intensity Scale

Intensity Description

I Not felt

II Felt by persons at rest on upper floors

III Felt indoors-hanging objects swing. Vibration like passing of ligth truck

IVVibration like passing of heavy trucks. Standing automobile rock. Windows, dishes, and doors rattle; wooden wall or

frame may creak.

VFelt outdoors. Sleepers weakened. Liquids disturbed, some spilled; small objects may be moved r upset; doors swing;

shutters and pictures move.

VIFelt by all; many frightened. People walk unsteadily; windows and dishes broken; objects knocked off shelves, pictures

off walls. Furniture moved or overturned; weak plaster cracked. Small bells ring. Trees and bushes shaken.

VIIDifficult to stand. Furniture broken. Damage to weak materials, such as adobe; some cracking of ordinary masonry. Fall

of plaster, loose bricks, and tile. Waves on ponds; water muddy; small slides along sand or gravel banks. Large bells ring.

VIIISteering of automobiles affected. Damage to and partial collapse of ordinary masonry. Fall of chimneys, towers. Frame

houses moved on foundations if not bolted down. Changes in flow of springs and wells.

IXGeneral panic. Frame structures shifted off foundations if not bolted down; frames cracked. Serious damage even to

partially reinforced masonry. Underground pipe broken; reservoirs damaged. Conspicuous cracks in ground.

X Most masonry and frame structures destroyed with their foundations. Serious damage to dams and dikes; largelandslides. Rails bent slightly.

XI Rails bent greatly. Underground pipelines out of service.

XII Damage nearly total. Large rock masses shifted; objects thrown into the air.


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Tsunami:A tsunami develops when part of the sea floor drops during an

earthquake. Water rushes to fill the low spot, but the inertia of the

rushing water forces too much water into the area, creating a bulge inthe water surface. The long, shallow waves can build up into

destructive giants when they reach shore.


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Tsunami due to

down faulting of

sea floor
http://localhost/var/www/apps/conversion/tmp/scratch_4/video%204/Pergerakan%20Lempeng%20_gel%20S_2.flv


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Indonesia, 2004

~49 m

>200,000 killed


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EARTHQUAKE IN INDONESIA

For the last few years, earthquakes have occurred inIndonesian archipelago, such as those in Sumatra, Java, and

Sulawesi-Maluku-Papua. However, this lecture may emphasize

on earthquakes occurred in Sumatra and Java, especially

those caused very serious damage.

The most damaging earthquake is that followed by tsunami

took place in Aceh on December 26th, 2004, in which more

than 200.000 people were killed, tens of thousand of missing

people, and a million of homeless.


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TSUNAMI MECHANISM IN ACEH


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hypocenter: 3.307Nand 95.947E; 160 km west of Sumatra; at a depth of

30 km below MSL

Moment magnitude (Mw): 9.0 (USGS)

Total energy released: 4.3 x 1018joules equivalent to 100 gigatons of TNT

Movement along the fault line: 10 m laterally and 4-5 m vertically

Tsunami waves: up to 48.9 m high with a tsunami magnitude (Mt) of 9.1

Greatest strength of tsunami waves: an east-west direction

EARTHQUAKE IN ACEH


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EARTHQUAKE IN ACEH: 26 December 200400:58:53 GMT/07:58:53 WIB Western Coast of North Sumatra

In this region, earthquake was followed bytsunami (30 minute after shocks), the

damage was caused by seismic ground

motion

Approximate damage:

Death: 200,000 to 300,000; missing>51,000; and homeless >1,000,000

One-third of the dead appear to be

children Why? Students should

discuss it in a group.

As four times as many women thanmen were killed Why? Students

should discuss it in a group.

Other victims: traumatic survivors

FACTORS considered tobe partly responsible for

the great human loss of

life include:

People lived on low-lying

coastal areas without

refuge buildings

Lack of earthquake and

tsunami knowledge

There was no an early

tsunami warning system


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Number of tsunami victims in Aceh by region


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EARTHQUAKE IN ACEH

Infrastructures: Houses and other buildings

around the coastal regionwere destroyed.

Other facilities such astransportation andcommunication (failure of50,000 telp lines) caused thecoastal region isolated.

Up to 2 km away fromcoastline every single thingwithout exception (~100%)was washed out by tsunami

Between 2-3 and 5 km fromcoastline structures weremostly washed out bytsunami.

The rice field was submerged

near the coast at Piukan Bada


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Physical Impacts due toTsunami in Aceh


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FACTORS INFLUENCING DAMAGES

1. Collapse of Buildings due to

Seismic Ground Motion:(a) Influence of period of

seismic motion

(b) Influence of the long

duration of the quake

2. Collapse of Buildings due toTsunami:

(a) Estimated by using washout

ratio, based on satellite

imagery data before and

after tsunami

(b) Influence of distance from

shore lineMosque could remain after tsunami

attack WHY? STUDENT

DISCUSSION


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TSUNAMI HEIGHTS

15-30 m on the west coast

6-12 m on the Banda Aceh

coast

~6 m on the Krueng Rayacoast

~5 m on the Sligi coast

3-6 m on Weh Island


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Tsunami traces found in Leupung. HereTsunami was up to 30.5 m high.

A family house located ~1,3 kminland in Banda Aceh

Coral stone transported by tsunami

A family house located ~0,9 km from the coast.Also shown are inundation depths

TSUNAMI IMPACTS IN ACEH


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TSUNAMI IMPACTS IN ACEH

No Region Impacts

1 Banda Aceh

Residential zone between coastline and city center was

completely destroyed

Commercial zone & Government Offices escaped total

destruction, but were damaged badly by the flood

Most of the dead & missing people came from these zones

2 SW Coast

Towns, villages, and infrastructures (roads & bridges) were

destroyed

Towns & villages were totally isolated accessible only by boatand by helicopter (STUDENTS SHOULD DISCUSS ANY

CONSEQUENCES OF THIS CONDITION)

3 N Coast

Tsunami did not inflict severe damage, compared to other

regions (except several fishing villages)

Local society was greatly affected by tsunami, because

survivors from SW coast flocked into towns & villages in N coast

Less aid as it was considered less affected. This could cause

future social uncertainties (STUDENTS SHOULD DISCUSS IT)

DISTRIBUTION OF COMPLETELY COLLAPSED


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DISTRIBUTION OF COMPLETELY COLLAPSED

BUILDINGS DUE TO SEISMIC GROUND MOTION

KERUSAKAN ASET KEHANCURANINFRASTRUKTUR SOSIAL


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BUDAYA

Perpustakaan IAIN Ar-Raniry :7.000 buku rusak

Perpustakaan Universitas SyahKuala : Bangunan retak, rakbuku rubuh, keramik pecah-pecah, plafon berjatuhan.

Perpustakaan Ali Hasjimy untukPendidikan : buku-buku

berjatuhan ke lantai ketikagempabumi

Makam Syiah Kuala (ulamaabad 16) : utuh, hanya banguandisekitarnya yang rusak/hanyut.

Sertifikat tanah 3-4% rusakkarena tsunami menyebabkan

masalah kepemilikan tanah

Berhentinya fungsi pemerintahan

Gempabumi dan tsunami

menghancurkan pusatpemerintahan di :

Banda Aceh (Ibu kota NAD)

Calang (Kota utama di Aceh

Jaya)

Meulaboh (Kota utama diAceh Barat)

Pejabat pemerintah di provinsi

dan kabupaten/kota menjadi

korban, termasuk Walikota

Banda Aceh. Kesulitan

INFRASTRUKTUR SOSIAL


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1964

1822

1892 (7 7)

Historical Earthquakes along The Sumatran Fault Zone


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19211916

1984

1987

1892

1822

1943

1909

1995

1952

1926

1942

1893

1900

1933

1994

1908

1990

1997

1936

1964

1967

1926 (~7)

1984 (6.4(

1987 (6.6)

1893

1892 (7.7)

1900

1908

1916

1933 (7.5)

1942 (7.3)

1936 (7.2)

1952 (6.8)

1979 (6.6)

1943 (7.3)

1990 (6.5)

1997 (6.5)

1964 (6.5)

1921 ( >7)

1994 (6.9)

1995 (7.0)

1909 (7.6)

1967 (6.8)

2000

Seismic Gap?

23 destructive events in the past 200 years or

1-2 large earthquakes occur every decade

6 Maret 2007

(M6.3 & 6.1)

(sumber: Natawidjaja)

Earthquake in West Sumatra and Yogyakarta


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Earthquake in West Sumatra and Yogyakarta

Earthquake occurred on May 27th, 2006 05:53:57 WIB; 8.00 LS-110,31 BT,32,2 km south Yogyakarta City; 5,9 Richter Scale.

Dead > 10.000 people, injured ~47,000 people, Homeless > 3,400,000orang

Damaged houses : >130.000 (heavily destroyed); >190.000(moderately destroyed) and >278.000 (slightly destroyed )

Earthquake on March 6th, 2007; 10:49:39 WIB; Hypocenter : 0.55 LS -100.47 BT Depth: 33 Km, Magnitude 5.8 RS, located inland 16 km SWBatu Sangkar West Sumatra.

Victims : dead 72; badly injured 504; slightly injured 134.

Damage : 4.085 houses (heavily destroyed); 1,783 houses (moderately

destroyed) dan 4.015 houses (slightly destroyed ); 176 religiousfacilities, 172 educational facilities, 84 offices and 49 public facilities

Homeless: in Solok Distric up to 6,568 people.

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