Transcript Just-in-Time Lecture Earthquake & Tsunami South Asia, 26 Dec 2004 By: Ali Ardalan, Ronald E.

Just-in-Time Lecture
Earthquake & Tsunami
South Asia, 26 Dec 2004
By: Ali Ardalan, Ronald E. LaPorte, Eugene
Shubnikov, Faina Linkov & Eric K. Noji
 What is the Disaster Supercourse?
 What is a JIT lecture?
Mission Statement:
The Global Health Network Disaster,
Network for Tsunamis is designed to
translate the best possible scholarly
information from leading researchers
to educators worldwide.
Lecture objectives:
 To provide the best possible information
about the science of South Asian disaster
Earthquake & Tsunami: South Asian
 Greatest earthquake in 40 years
 Magnitude 9.0 on Richter scale
 150 km off W coast / N Sumatra Island / Indonesia
 Generation of disastrous
tsunami in 11 countries
bordering Indian Ocean
History of Great Earthquakes in the Region:
Along the subduction zone from
southern Sumatra to the Andaman Islands
 2000: M 7.9
 1861: M 8.5
 1833: M 8.7
 1797: M 8.4
USGS
Magnitude 9.0 on Richter scale
• The 4th largest earthquake in the world since 1900
• The largest since 1964 Alaska earthquake
----------
It was felt (VIII) at Banda Aceh, (V) at Medan,
Sumatra & (II-IV) in parts of Bangladesh, India,
Malaysia, Maldives, Myanmar, Singapore, Sri Lanka
& Thailand.
Earthquake Strength Measures
I) Magnitude & II) Intensity
I) Magnitude:
 Definition: A measure of actual physical
energy release at its source as estimated from
instrumental observations.
 Scale: Richter Scale
 By Charles Richter, 1936
 Open-ended scale
 The oldest & most widely used
Noji 1997
Earthquake Strength Measures
I) Magnitude & II) Intensity
II) Intensity:
 Definition: a measure of the felt or perceived
effects of an earthquake rather than the strength
of the earthquake itself.
 Scale: Modified Mercalli (MM) scale
 12-point scale, ranges from barely
perceptible earthquakes at MM I to
near total destruction at MM XII
Magnitude versus Intensity
 Magnitude refers to the force of the earthquake as
a whole, while intensity refers to the effects of an
earthquake at a particular site.
 An earthquake can have just one magnitude, while
intensity is usually strongest close to the epicenter
& is weaker the farther a site is from the epicenter.
 The intensity of an earthquake is more germane to
its public health consequences than its magnitude.
Duration of the Earthquake
 Actual rupture duration: 3- 4 min.
 Definition: The time it took for
earthquake to take place on
fault & rupture entire length
Northern Sumatra: Above the fault
Felt shaking: Several minutes
USGS
Unbelievable !!
Earthquake = 23,000 Hiroshima Bombs
Released Energy by South Asian Earthquake
Es 20X10^17 Joules
=
475 megatons of TNT
USGS
Effect of the Earthquake on the
Length of Day
-2.676 microseconds
Too small to be observed !
USGS
Earthquake 26 Dec 2004
 Max. displacement on the rupture
surface between plates: 20 m
 Max. displacement of sea bottom
above the quake source: 10 m
USGS
Rupture a patch along fault's
surface by earthquakes
Larger the rupture patch, Larger the
magnitude of earthquake
as BIG as California !!
Patch of fault by Sumatra-Andaman
Islands Earthquake
How we can estimate the initial size
of the rupture by an earthquake?
By studying:
 Length of the aftershock zone
 Dimensions of historical earthquakes
 Generated elastic waves
Aftershocks
 As 29 Dec: 68 aftershock
 M 7.1: The largest, 3h after the main shock
 M ≥ 6.0: 13 aftershocks
The Earthquake Rupture’s Length & Width
 Length: 1200-1300 km
 Width: >100 km
USGS
 NO tsunamis by the aftershocks in south Asia
 Number of aftershocks will decrease with time
 Number of aftershocks can be quite variable.
Seismologists are not able to predict
timing and sizes of individual
aftershocks !
USGS
Earthquake 26 Dec 2004
 Location: Beneath the Indian Ocean west
of Sumatra, Indonesia
 Epicenter: East of the Sunda Trench
 Overriding plate: Burma Plate
 Subducting plate: India Plate
What is a Megathrust Earthquake?
&
What is the Thrust-Faulting?
26 Dec 2004: Result of Thrust - Faulting
Megathrust earthquakes occur where
one tectonic plate subducts
beneath another.
Importance of Megathrust Earthquakes
 World's largest recorded earthquakes have all
been megathrust events
 Often generate large tsunamis that cause
damage over a much wider area than is directly
affected by ground shaking near the
earthquake's rupture
NEIC
The megathrust earthquake of
Dec 26, 2004, occurred on the interface
of India and Burma plates and was
caused by the release of stresses that
develop as the India plate subducts
beneath the overriding Burma plate.
NEIC
History of Megathrust Earthquakes
 1960 Chile, M 9.5
 1964 Prince William Sound, Alaska, M 9.2
 1957 Andreanof Islands, Alaska, M 9.1
 1952 Kamchatka, M 9.0
NEIC
What is a Tsunami?
 soo-NAH-mee or Harbor Wave
is a Japanese word: tsu means
harbor & nami means wave
History of Significant Tsunamis in the Region
1797: > 300 fatalities at Padang, M 8.4 EQ
1833: Numerous victims at W Sumatra, M 8.7 EQ
1843: Many fatalities at the coast of Nias Island
1861: 1000s fatalities at W coast of Sumatra, M 8.5 EQ
1881: India’s eastern coast, M 7.9 EQ
883: 36,000 fatalities on islands of Java & Sumatra,
Krakatau explosion
1941: M ~7.7 Adaman Islands EQ ( Anecdotal evidence
of existing a tsunami)
USGS
NASA
How the earthquake 26 Dec 2004
generated tsunami?
Imagine a fist rising up from under the water.
Water rolls down off the sides of the fist.
When the bottom of the ocean was deformed
by this megathrust quake, the upward force
acted like that fist, creating massive waves of
tsunamis, which spread out in all directions.
Tsunami: 2 Wavefronts
 Distance: 500 - 850 km
 Height: 50 cm
Tsunami Waves: Height & Travel time
 Height:
• 10 m: Coastline of
Sumatra, near the
fault boundary
• 4 m: Sri Lanka,
Thailand, Somalia
& Seychelles
 Travel times:
From minutes (Sumatra)
to 8 hours (Somalia)
Tsunami: Distance & Damage
 Distance alone: NO guarantee of safety
 Somalia was hit harder than Bangladesh
despite being much farther away.
NASA
Andaman Islands
• One of the first affected
places, Dec 26
• 850 km N of epicenter
• As 3 Jan: > 6000 death
The Most Affected Area by the Tsunami
NW coast of Sumatra, Aceh province,
Indonesia
 100 km (62 miles)
from the epicenter
 Waves height:
15 m. (50 ft.)
 80,000 death
(1/2 of total)
Tsunami: Sri Lanka & India
 Waves travel time: 4h
Devastation the island of Sri Lanka off the
southeastern tip of India
 Moving the waves westward toward
southeastern India, along a stretch of coastline,
Coromandel Coast
 Destruction of cities, towns, and fishing villages
up and down the coast of state of Tamil Nadu
NASA
Tsunami: Thailand
 Beaches of Khao Lak: struck 2-3 h after
the earthquake
 Location: 500 km from the epicenter
 Waves height: 10 m. (33 ft.)
NASA
Tsunami: Maldives
Male, the capital island of Maldives
was severely hit.
NO Tsunami Warning Issued on 26
Dec 2004 Disaster !!
NO Tsunami Warning System
exists for the Indian Ocean !!
Knowledge is Safety!
Girl's sea warning saved a hundred fellow
tourists at Phuket beach from tsunami because
of a geography lesson about the giant waves!!
The impacts of earthquake
& tsunami on South Asia
 Dead:139.290
 Injured:32,327
 Missed:14,950
 Displaced: 1,754,433
WHO
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