03/000

Phil R. CumminsMarch 2005

The Indian Ocean Tsunamis – Science and Seismics

Australian Government

Geoscience Australia

Outline

• The physics of tsunami generation.• Why the occurrence of large, Indian

Ocean-wide tsunami should have been foreseen prior to 26 Dec. 2005.

• The 2004 Boxing Day Earthquake & Tsunami.

• Comparison with 2005 Easter Earthquake and ‘non-tsunami’.

• Suggestions for future research.

Plate Tectonics & Subduction

Zones

Earthquake Excitation of Tsunami

Comparative Tectonics: M>8 Earthquakes: Japan vs

Indonesia

Japan

Indonesia

Tsunami Generated by

the Great Sumatran

Earthquake

Of 1833

(Mw=9.2)

From Park

et al., EOS

2005

Seismic Waves Generated by the Great

Sumatra- Andaman Earthquake of 2004

26 Dec Sumatra Earthquake

Fault movement occurred over a 1300 km length, but seismic and tsunami waves were generated over a more limited region

Crustal Movement in Andaman Islands

(from Roger Bilham’s

Web site)

Free Oscillations – Mw=9.3!

 

Stein et al.’s analysis of free oscillation data shows that the Sumatra-Andaman earthquake had an Mw=9.3, making it the 2nd largest earthquake ever recorded.

Effects in Sumatra

The first effects of the tsunami were felt in Sumatra, where villages along the coast were razed completely by waves of 10-30 metres in height.

(Results of survey by lead by Prof.

Tsuji of Tokyo’s Earthquake Res. Inst.)

Tsunami Waves

Le Havre, France

Phuket

Bay of Bengal

28 March, 2005 Sumatra Earthquake

↑ Slip model obtained by Chen Ji, Caltech

← Image from USGS

2004 & 2005 SumatraEarthquakes2004 2005

Fau

lt S

lip

Ver

tica

l S

eafl

oo

r M

ove

men

t

(Slip models from

Chen Ji, Caltech)

Conclusions• Evidence existed prior to 26/12/2005 that Indian Ocean-

wide tsunami were generated by M≥9 earthquakes offshore

Sumatra.

• The Great Sumatra-Andaman Earthquake of 2004 ruptured

a 1300 km section of the Sumatran subduction zone,

making it the 2nd largest earthquake ever recorded.

• Comparison with the Great Sumatran Earthquake of 2005

suggests that the latter generated a small tsunami because

of the concentration of fault slip at depth.

Geoscience Australia

Geoscience Australia

Mar 2005 – NAF

Suggestions for Future Research on Indian Ocean

Tsunami• Collection & analysis of historical and paleotsunami data to characterize the hazard.

• Modeling & analysis to quantify tsunami risk.• Geodetic monitoring of strain accumulation in

subduction zones.• Further work on tectonic history of the Indian Ocean.• The above should take into account the Makran

subduction zone offshore Iran-Pakistan border, as well as Indonesia.

• Better collaboration among Indian Ocean & Pacific countries, and among earthquake & tsunami researchers.