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Assoc. Prof. Dr. Wan Zuhairi Wan Yaacob

Program Geologi

UKM

G E M P A B U M I

(EARTHQUAKE)

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10 largest earthquake in the world

1. Chile (9.5) -- 1960

2. Alaska (9.5) -- 1964

3. Northen Sumatera (9.1) – 26.12.2004

4. Kamchatka (9) -- 1952

5. Equador (8.8) -- 1906

6. Alaska (8.7) - 1965

7. Northern Sumatera (8.6) – 28.03.2005

8. Tibet (8.6) - 1950

9. Alaska (8.6) - 1957

10. Benda Sea Indonesia (8.5) - 1938

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Earthquake in Turkey(August 17, 1999); killed 15,000

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Turkey Earthquake

• Magnitude 7.4

• August 17, 1999

• Killed 15,000 people

• Poor and improper

construction of

buildings (seismic

shaking)

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MIRACULOUS: A mosque is

seen still standing of the town

of Meulaboh, Aceh Province,

Indonesia. (150km dari

epicentre, 10,000 mati)

PENGAJARAN !!!!???

Sedutan dari Akbar harian:

“Satu fenomena yang menunjukkan

kekuasaan Tuhan dan binaan yang

bagus”

“Dia menghukum kita kerana

keangkuhan tetapi melindungi

rumahnya”

“Ujian dari Allah”

“saya memanjat menara masjid dan

memegang kuat wayar eletrik hingga

air surut”

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Earthquake catastrophic

Date Place Magnitude People killed

16th century

(1500s)

China 850,000

1886 South Carolina,

US

60

1906 San Francisco 700

1923 Tokyo 143,000

1976 China 650,000

1985 Mexico 10,000

1989 San Francisco 62

1993 India 6.3 7600

1994 Los Angeles 6.6 (1m

uplift!!)

61/51

1995 Kobe, Japan 5000

2004 Sumatera 9.0 250,000

Apakah penyebab perbezaan kematian di India dan LA ??

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Animas

90% of earthquakes occur at or near

plate boundaries animas

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Manusia tinggal dekat dengankawasan bencana

1,300 kilometres

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EARTHQUAKE

The vibration of earth caused

by sudden release of

energy beneath earth’s

surface, usually as a result

of displacement of rocks

along fractures known as

faults.

Haiti earthquake

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Old ideas

• The movement of some organism

on which Earth rested.

• Japan – giant catfish

• Mongolia – giant frog

• China – an ox (large horned

animal)

• India – giant mole (burrowing

animal)

• South America – whale

• Dragon ???

• Aristotle : atmospheric winds

God is angry, or else the

plates along San Andreas

fault have slipped again

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New Ideas

• Faults (especially plate boundaries)-

Richter, 1958

• Landslides

• Volcanic Eruptions

• Filling of Reservoirs (Dams)

• Atomic Explosions

• Conspiracy theory - HAARP

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Elastic rebound theory

(teori pantulan kenyal)Slow deformation of the crust (creep) until strength of rock is exceeded.

Then, rupture occurs (earthquake).

Eg: 1. 50 years before 1906 San Francisco earthquake – offset creep 3m

2. Movement during earthquake 6m in 40 seconds !!

-Keadaan saling mengunci

-Gelinciran tertangguh lama

-Pengumpulan tenaga keterikan kenyal

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How does it

happen?

Elastic Rebound

Theory

(Teori elastik

balikan semula)

Teori pantulan

kenyal

ANIMATION

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Terminology

• EPICENTER / epipusat: location of earthquakes projected at the surface.

• HYPOCENTER or FOCUS/Foci: where earthquake actually happened. Location of the earthquake at depth. Epicenter is directly above the hypocenter.

• Main Shock: Largest and generally First earthquake in a sequence.

• Aftershock: Smaller earthquakes after first main shock. Can last as much as a month afterward. Can be almost as large as main shock, generally smaller. Decrease in magnitude with time.

• Foreshock: An earthquake that occurs prior to a large one.

Foreshocks & Aftershocks

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FORESHOCKS

-Hours/days before

-Does not always occur

MAJOR EARTHQUAKE

(main shock)

AFTERSHOCKS

-minutes to months

after major quake

animation

Fault Activity

• Fault Activity:

– active if moved during the

past 10,000 years (Holocene

Epoch);

– Potentially active (1.65 M –

10,000 years);

– Inactive (>> 1.65 M)

• Nuclear power plant

– once in 50,000 years

– >once in 500,000 years

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• 2 concepts:-

– (1) Slip rate : ratio of displacement to time interval

• Eg: 1 m displacement in time interval 1000 years;

then slip rate is 1mm per year

– (2) Recurrence interval

3 methods:-

• (i) Paleoseismic data : average time intervals between

earthquake (setiap 100 tahun?)

• (ii) Slip rate : Eg – 1 m average displacement per event;

slip rate 2 mm per year; recurrence interval = 500 years

• (iii) Seismicity: using historical earthquake & averaging the

time (sama spt (i)??)

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Fault Activity

Tectonic creep

• Rayapan tektonik

• Tectonic creep is the almost

constant movement of

certain fault blocks that

allows strain energy to be

released without causing

major earthquakes.

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Soil creep

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Pengelasan gempa berdasarkan kedalaman titik

focus

– Shallow focus (0-

70km)

– Intermediate focus (70

– 300km)

– Deep focus (300 –

700km)

(little/no damage)

-- >700km ???

More frequent

Mantle behaves plastically; deforming

continuously as ductile substances, no

storing up strain energy

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Seismic waves

• BODY WAVES (travel thru earth)

– (i) P waves or primary

– (ii) S waves or secondary

• SURFACE WAVES (travel along the

surface)

– (i) Rayleigh waves

– (ii) LOVE waves

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BODY WAVES

– (i) P waves or primary

• Fastest waves; P wave velocity = 6 km per second

• Travel thru solids;liquids;gases

• Mechanism: Push-pull/expanded-compressed

• Return to original volume

• Compressional waves (movement of particles in the

direction of wave movement), like sound waves

– (ii) S waves or secondary

• Slower than P-waves (3.6 km/sec).

• Travel thru solids only

• Shear waves (gelombang ricih)

• Move material perpendicular to the direction of travel

• Like ocean waves

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SURFACE WAVES

• Slower than body waves

• Produce a rolling and swaying motion

• Surface waves confined to the Earth’s surface like ocean waves.

• Surface waves are very destructive

• (i) Rayleigh waves– Rock particles move in vertical rolling motion (orbital).

• (ii) Love waves– Rock particles move SIDE-SIDE in a horizontal plane

– Travel faster than Rayleigh.

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Seismic waves

Body waves

Surface waves

swaying

rolling

Wave

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Comparing Earthquake

1.Calculate the energy released (Magnitude)

Quantitative measurement of energy released

2.Evaluate the impact on people and

structures (Intensity)

Qualitative assessment of the kinds of damage done

3.Ground accelerations (measure the severity

of ground shaking

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How Are Earthquake Magnitudes Measured?

• The Richter Scale– invented by Charles F. Richter &

Beno Gutenberg in 1934 (1935?) - seismologist

– is calculated from the amplitude of the largest seismic wave recorded for the earthquake

• The Mercalli Scale– Invented by Giuseppe Mercalli in

1902

– the observations of the people who experienced the earthquake to estimate its intensity

Charles Richter studying a seismogram

(From Walker, 1982)

Giuseppe Mercalli (From Walker, 1982)

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1st Seismologist !!

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Seismograph

Konsep Inertia

“Suatu jasad akan tetap berada dalam keadaan pegun”

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Seismogram

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Sumatera Earthquake Dec, 2004

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Richter magnitude, M (quantitative)

- Calculation of the amount of energy released during earthquake

–Based on seismograph

–Size of earthquake

–9.5 (largest recorded). MAX – 10; >9 improbable (mustahil kerana batuan).

– Intensity --- depends on Geology: unconsolidated sediment > hard rock

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– The scale is logarithmic

• M7 = 10x ground motion (disturbance/amplitude)

M6

• M7 = 301x energy released M6

• M8 = 900 x (=302) energy of M6

• M7 = 27,000 x (=303) energy of M4

• M2 – the smallest quake felt by humans

• M5 – potential damage

• 1906 San Francisco earthquake M8.2

• 2004 Sumatera Earth Quake M9.0

“A magnitude ZERO earthquake is about equal in energy

to a stick of dynamite” – Dutch et al.

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Three types of Richter Magnitude

• ML = Local magnitude (the largest seismic wave regardless of type, P, S, SS)

• Mb = Magnitude is based on P wavesb – body wave

• Ms = magnitude is based on surface waves

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Moment Magnitude, Mw

• 1979; Thomas Hanks & Hiroo Kanamori

• not based on seismometer readings

• Based on seismic moment (Mo)

– Mo = average displacement on the fault x the

rupture area x rigidity of rock (i.e. shear

modulus ; resistance to shear stress)

• Mw = 2/3 log Mo – 10.7

• 10.7 is a constant

• Eg. Chilean earthquake (Mw=9.5 / M = 8.3)

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12

3 4

Finding the Distance to the

epicenter and the

earthquake's magnitude

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Finding the Epicenter

1

3

2

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Earthquake Magnitude Classes

Earthquakes are also classified in categories ranging from minor to great,

depending on their magnitude

.

ClassMagnitude

Great 8 or more

Major 7 - 7.9

Strong 6 - 6.9

Moderate 5 - 5.9

Light 4 - 4.9

Minor 3 -3.9

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Moment Magnitude, Mw

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Earthquake Richter Magnitude Scale

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Modified Mercalli Intensity Index (MM)

Measure the damage and felt intensity

(observation)

Site examination and interviews;

photographic; Questionnaire.

Decrease from the epicenter

12 divisions of intensity

Intensity range I-XII (roman numerals)

Intensity II – felt by people

Intensity X – heavy damage !!!

Intensity map

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Intensity I : Not felt except

by a very few under

especially favorable

circumstances

Intensity III : Felt quite

noticeably indoors,

especially on upper floors

of buildings, but many

people do not recognise it

as an earthquake

Intensity XII : Damage

total. Waves seen on

ground surfaces. Objects

thrown upward into air

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Intensity map

(isoseismals)

Q: kenapa di Oakland intensiti

gempa adalah VIII?

Gempa bumi Malaysia

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Gempa bumi Malaysia

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Ground acceleration during

earthquakes• measure of earthquake

acceleration on the ground

(i.e. how hard the earth

shakes)

• Important input parameter for

earthquake engineering –

bridge, building, etc.

• Expressed in g (the

acceleration due to Earth's

gravity) or in m s-2 (1 g = 9.81

m s-2).

• M 6-6.9 = acceleration 0.3 to

0.69g

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Shaking table – Kyoto Uni, Japan

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Man Made Earth Quake

• Building big dam or reservoir (Reservoir Induced Seismicity)

– Hoover Dam in US

• Load of water

• Infiltration of water into fractures/faults

• Magnitude 5

– Koyna, India 1962

• 6.5 quake in 1967 killed 177

• Disposing liquid waste into ground (disposal wells)

– 1986 quake in Ohio

– 1962—1965; Rocky Mountain Arsenal

– Strong correlation: amount of fluid and number of earthquakes

– Increase fluid pressure

• Underground nuclear explosions

– Earthquake M 5 to 6.3

Malaysia = Tasik Kenyir!!?

HAARP PROJECT

• Video

• China earthquake

caused by HAARP

weapon ???

• High Frequency

Active Auroral

Research Program

(HAARP)

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The amount of damage depends upon:-

• Geology– Mexico City earthquake; alluvium (lake deposits);

– but epicenter on solid rock; hundred kms away; M8.1

• Type of buildings– natural vibration frequency of the buildings vs

frequency of the seismic waves

• Magnitude

• Duration of shaking

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animation

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Effects of Earthquakes

• Primary effects

Caused directly by the phenomena

– Violent ground motion

– Surface rupture

– Permanent displacement / fault rupture

– Snap and uproot large trees and knock

people to the ground

– Shear/collapse large buildings; dams;

tunnels; pipelines; other rigid structure

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1992 M 7.5 Landers, CA fault scarp

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• Secondary effects

– Short range events:--• Tsunamis

• Liquefaction

• Landslides

• Fires

• Floods

– Long range effects:--• Regional subsidence

• Regional changes in groundwater level

Effects of Earthquakes

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Liquefaction

animation

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Mitigation Strategies

Mitigation Strategies:–

• Hazard Maps

• zoning, building

codes, emergency

plans

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Risiko dan Jangkaan Gempabumi

• (1) Jangka Panjang

– Kaedah keberangkalian utk menentukan

risiko kejadian gempa sepanjang satah

sesar / kawasan ttt

• Membantu perancangan guna tanah

(penempatan)

• Seismic hazard map (Peta risiko seismik)

– Paleoseismology

– Zon senyap seismik (seismic gap)

• Zon aktif sesar senyap (store tectonic strain)

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Hazard Maps

Probabilities and expected magnitudes of future California earthquakes

A diagram showing the probabilities and magnitudes of future earthquakes in California

from 1988 to 2018

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Paleoseismology

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Seismic gap

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Seismic gap

(2) Jangkaan jangka pendek:-

• Perubahan bentuk muka bumi

– Pengangkatan (uplift) yang berlaku

• Patterns and frequency of earthquakes

– (i) reduction in small/moderate

earthquakes prior to larger event

– (ii) small earthquake may tend to ring the

area.

• Foreshocks Water; Level in Wells; Emission

of Radon Gas

• Strange animal behavior

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Protective measures / mitigation

• Structural protection

• Land use planning

• Insurance

• Duduk diam dan tunggu !!

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Statue of Louis Agassiz, the great geologist at Stanford Uni after 1906

earthquake

TAMAT

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