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The December 26, 2004 Mw 9.0 Western Sumatra Earthquake
and Tsunami
Michael Bunds
Department of Earth Science
Utah Valley State College
The Earthquake’s Statistics
Magnitude 9.0 (Mw)
Sunday, December 26, 2004 at 00:58:53 (UTC)Sunday, December 26, 2004 at 7:58:53 AM local time at
epicenter Saturday, December 25, 2004 at 5:58:53 PM Mountain Standard
Time
Energy Released = 2 x 1017 JoulesEquivalent to 475 megatons of TNT or 23,000 Hiroshima bombs
Tsunami energy estimate = 1014 Joules (10 Hiroshima bombs)
Over 225,000 fatalities, 5 million homeless people in Indian Ocean – most as a result of earthquake-induced tsunami
The Earthquake in Historical ContextFour Largest Earthquakes on Record
1. M 9.5 Chile, 1960
2. M 9.2 Prince William Sound, Alaska 1964
3. M 9.1 Andreanof Islands, Alaska, 1957
4. M 9.0 Kamchatka, 1952
5. M 9.0 Sumatra, 2004
1
234
5
10 of 11 largest on subduction zone megathrusts surrounding Pacific Ocean
Most deadly tsunami recorded history
Destructive historical tsunamis at the
western coast of Sumatra
1797/02/10 M>8.0 Central part of the western Sumatra. Padang was flooded by powerful waves. More then 300 fatalities. 1833/11/24 M=8.8-9.2 South coast of the western Sumatra. Huge tidal wave flooded all southern part of the western Sumatra. Numerous victims. 1843/01/05 M=7.2 Terrible wave came from the south-east and flooded all the coast of the Nias Island. Many fatalities. 1861/02/16 M>8.2 Several thousand fatalities.
What is an Earthquake?
Ground shaking caused by a sudden release of energy within Earth.
Most result from slip on a fault.
Elastic Rebound
Original Position
200 to 500 years later
Overriding crust flexes 10 to 50 meters, storing energy to be released in earthquake
During earthquake
Overriding crust snaps back to original position
200 – 250 km wide areas uplift and subside
SubsidenceUplift
SumatraAndaman Isl.
M9.0 Epicenter
U.S.G.S
Aftershocks (yellow circles) outline
ruptured area on fault
~1200 km by 200 km area of fault
ruptured
U.S.G.S
Expected Areas of
Uplift and Subsidence
Andaman Islands
Probable area of
subsidence
Probable area of uplift
Andaman Islands
Probable tectonic
uplift from earthquake
Andaman Islands
Probable tectonic
uplift from earthquake
BeforeBefore AfterAfter
Andaman Islands
Probable tectonic
uplift from earthquake
Andaman Islands
Probable tectonic
uplift from earthquake
BeforeBefore AfterAfter
Submerged coral reef
Emergent coral reef
Generalized Tsunami Wave Characteristics
• Usually more than one wave is created• In open ocean
– Wavelength: 200 to 250 km (dist. between wave peaks)– Wave height: 0.5 m– Speed: 700 km/hr– Period: 17 minutes (time between wave peaks)
• Near shore– Wavelength: 10 km– Wave height: meters to tens of meters– Speed: 36 km/hr– Period: 17 minutes (time between wave peaks)
Waves Compress as They Near LandWaveheight increases
Wavelength decreases
But tsunamis do not break like the pictured wind waves
Wind waves are tall and
short wavelength
Tsunamis often are no taller than
wind waves, but
involve much more water due
to long wavelength
Variations in Tsunami Intensity
An individual tsunami can have vastly different heights in different places depending upon:
– Distance and direction from source– Wave source directivity (most wave energy was
directed east and west)
– Configuration of local seafloor and coastline
– Shielding by other landmasses
Sumatra, north-west coast 10-15 m
Sri Lanka, east coast 5-10 m
Thailand (incl. Phuket) 3-10 m
India, east coast 5-6 m
Andaman Islands > 5 m
Kenya 2-3 m
Sumatran Tsunami Maximum Heights
Additional Factor: In Thailand and Sumatra tsunami closely coincided with highest tide for the month