THE 2004 INDONESIAN EARTHQUAKE AND TSUNAMI: MITIGATION IMPLICATIONS FOR CASCADIA

The 2004 Indonesian earthquake raised global concerns about tsunami hazards and created an opportunity to promote tsunami mitigation programs. It has been particularly important for the Cascadia region of the Pacific Northwest where the last great earthquake occurred prior to European settlement and the nonscientific community has had a difficult time comprehending risk from technical evidence. The Indonesian earthquake provides a modern analog for the Cascadia hazard that may seem otherwise remote. Similarities between the Indonesian and Cascadia tectonic settings, the size of the two fault rupture zones, comparison of tsunami sediment deposits and drowned forests lend credibility to Cascadia's great earthquake past and tsunami hazard. The 2004 earthquake's most significant lesson for the Cascadia region is the importance of awareness and education in reducing loss of life. An International Tsunami Survey Team (ITST) studied the western coast of Aceh province, Simuelue and Nias Islands, Indonesia in April, 2005. Over 30 interviews with eyewitnesses were conducted by the ITST group in Aceh and an additional 10 on Simuelue Island. On the west coast of Aceh Province, peak tsunami water level heights averaged 15 to 20 meters and in some cases exceeded 30 meters. Time between the earthquake and arrival of the first tsunami waves was 15 to 30 minutes. Coastal villages were obliterated and survivor rates were typically 5% or less. All eyewitnesses claimed no awareness of tsunami hazards prior to December 26. In contrast, the northern part of Simuelue Island was closer to the fault rupture zone and had less than 10 minutes between the earthquake and tsunami. Peak tsunami water levels were lower than Aceh but still averaged over 10 m and all structures within the inundation zone were destroyed. Fewer than 10 fatalities were attributed to the tsunami on the entire island. The Simuelue people have kept alive the memory of a deadly tsunami in 1907 by giving it a name in their language (smong) and an oral history linking ground shaking and inundation. People are trained from a young age to immediately head to higher ground after an earthquake and stay away from low-lying areas for days. The story of the Simuelue people provides an excellent educational example for the Pacific Northwest.