Lessons from the 2004 Indian Ocean and 2011 Tohoku Tsunamis, Developments, and Future Directions

Abstract:

The 2004 Indian Ocean tsunami, the worst tsunami disaster in history with 230,000 casualties, was generated by the largest earthquake (M 9.1) since the 1960 Chilean and 1964 Alaskan earthquakes, but such a giant earthquake was not anticipated in the Indian Ocean. Besides its size, lack of tsunami warning systems in the Indian Ocean and lack of knowledge about tsunami among the coastal residents enhanced the tsunami disaster, while scientific knowledge and technology for far-field tsunami warning system existed. Developments since 2004 include paleo-tsunami studies, global tsunami observations and tsunami warning and hazard mitigation systems. Tsunami deposits found in Indonesia, Thailand and India show that giant tsunamis similar to the 2004 tsunami occurred in the past. Deep ocean pressure gauges (DART system), GPS buoys and coastal tide gauges have been installed with real-time data-telemetry capability in Indian Ocean as well as the Pacific Ocean. Three regional tsunami warning centers are now in operation in India, Indonesia and Australia. The 2011 Tohoku earthquake was also generated by a giant (M 9.0) earthquake. While such an earthquake was unexpected in Japan, similar tsunamis occurred in the past and caused damage on Sanriku coast and Sendai plain. The tsunami warning, issued 3 min after the earthquake, saved many lives yet caused significant (~19,000) fatalities, partly because of underestimation of earthquake size. The insufficient tsunami hazard assessment caused the significant number of casualties and the Fukushima nuclear power plant accident. Existed coastal sea walls might have given inappropriate belief to coastal residents that they were protected from tsunami disaster. Scientific and technological developments needed for the future include estimation of probable maximum earthquake size for tsunami hazard assessment, and real-time estimation of earthquake and tsunami size based on seismic and sea level measurements. In addition, limitation of scientific knowledge and technology need to be transmitted to coastal residents.