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

Phuket

Epicenter

Sri Lanka

Sumatra

Asia

CHINA

RUSSIA

INDIA

PhuketBandaAceh

Epicenter

Southeast Asia

Sri Lanka

U.S.G.S

Tectonic Setting

Subduction Zone

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

Hypocenter and Epicenter

epicenter

hypocenter

fault

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

Probable Tectonic Subsidence in Banda Aceh, Sumatra

eart

hob

serv

ato

ry.n

asa.

gov

Comparison of Sumatra Earthquake

Fault Rupture Area to Cascadia Subduction

Zone

U.S.G.S

Seismicityin Area

1900 – 2002, M > 6

Seafloor Displacement in Earthquake

Vertical uplift5 m max.

Horizontal movement11 m max. Cal Tech

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

Low Water Preceding Tsunami Wave in Sri Lanka

Usual water level

earthobservatory.nasa.gov

earthobservatory.nasa.gov

Sri Lanka

People Collecting Fish During Low Water Preceding a Tsunami. Oahu, Hawaii, 1957

U.S.G.S

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

A. Piatenesi, Tsunami Research Lab, Russia

Calculated Maximum Water Height

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

PhuketBandaAceh

Epicenter

Southeast Asia

Sri Lanka

earthobservatory.nasa.gov

Sri Lanka

Banda Aceh

Banda Aceh, Sumatra

Banda Aceh, Sumatraearthobservatory.nasa.gov

before after

Banda Aceh, Sumatraearthobservatory.nasa.gov

before

after

Banda Aceh, Sumatraearthobservatory.nasa.gov

before

after

Banda Aceh,

Sumatra

(before)

Banda Aceh,

Sumatra

(after)

earthobservatory.nasa.gov

Khao Lak earthobservatory.nasa.gov

before after

Banda Aceh, Sumatra (before)

earthobservatory.nasa.gov

Banda Aceh, Sumatra (after)

earthobservatory.nasa.gov

Banda Aceh, Sumatra (before)

earthobservatory.nasa.gov

Banda Aceh, Sumatra (after)

earthobservatory.nasa.gov

Lessons and Conclusions

• The earthquake and tsunami were not surprises

• Great earthquakes and tsunamis are rare but devastating

• Tsunami warning systems can save many lives

• If you are at the beach and you feel an earthquake, head for higher ground immediately