1. 03/000 Phil R. Cummins March 2005 The Indian Ocean Tsunamis – Science and Seismics Australian Government Geoscience Australia

2. 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.

3. Plate Tectonics & Subduction Zones

4. Earthquake Excitation of Tsunami

5. Comparative Tectonics: M>8 Earthquakes: Japan vs Indonesia Japan Indonesia

6. Tsunami Generated by the Great Sumatran Earthquake Of 1833 (Mw=9.2)

7. From Park et al., EOS 2005 Seismic Waves Generated by the Great Sumatra- Andaman Earthquake of 2004

8. 26 Dec Sumatra Earthquake Fault movement occurred over a 1300 km length, but seismic and tsunami waves were generated over a more limited region

9. Crustal Movement in Andaman Islands (from Roger Bilham’s Web site)

10. 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 2 nd largest earthquake ever recorded.

11. 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.)

12. Tsunami Waves Le Havre, France Phuket Bay of Bengal

13. 28 March, 2005 Sumatra Earthquake ↑ Slip model obtained by Chen Ji, Caltech ← Image from USGS

14. 2004 & 2005 SumatraEarthquakes 20042005 Fault Slip Vertical Seafloor Movement (Slip models from Chen Ji, Caltech)

15. 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 2 nd 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 Mar 2005 – NAF

16. 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.