A Probabilistic Tsunami Hazard Assessment of the Indian Ocean Nations
"This report is a result of collaboration by a team of earth scientists from Indian Ocean coun- tries to characterize the tsunami threat to the Indian Ocean region. The project was funded by the Australian Agency for International Development (AusAID), and was carried out under the auspices of Working Group 3 (Risk Assessment) of UNESCO’s Intergovernmen- tal Coordination Group for the Indian Ocean Tsunami Warning System (ICG/IOTWS), both of which recognized the need for a broad-brush tsunami hazard assessment that could guide Indian Ocean tsunami mitigation activities.
The project commenced with the UNESCO-IOC Workshop on Methodologies for Indian Ocean Hazard Assessment, convened in Bandung, Indonesia, 17-18 July 2007, and attended by experts in the geology, tectonics and earthquake activity nominated by IOC member states in the Indian Ocean region. The focus of the workshop was on assessing what information exists to constrain the probabilities and magnitudes of tsunamigenic earthquakes, and whether this information was sufficient for developing a useful tsunami hazard assessment. While the discussions recognized the important limitations of a broad- brush hazard assessment, it was recognized that a such an assessment would be an impor- tant step towards further work. The 2007 Bandung workshop resulted in the selection of a panel of scientists, each of whom visited Geoscience Australia to provide input into the probabilistic tusnami hazard assessment for the Indian Ocean presented here.
Two views quickly emerged in discussions among the panel of developers. The hazard assessment should, on the one hand, avoid over-estimating the hazard by considering only those sources for which there is solid evidence for generation of large tsunami. On the other hand, the assessment should be careful not to miss source zones that may generate large tsunami even if they have not done so historically - as was the case for the 2004 Indian Ocean Tsunami (IOT). The panel decided these two views could best be accommodated by developing two assessments, referred to here as low-hazard and high-hazard end member assessments. This affords a clear expression of uncertainty in the hazard as the difference between the two end members, while it was hoped that any additional confusion created in application of the two assessments to mitigation would be managable. The geographical pattern of the low-hazard assessment is broadly reflective of the impact of the IOT. The high-hazard assessment, on the other hand, highlights areas potentially threatened by local tsunami, such as the western Makran and southern Java coasts, which are at the same time the areas of highest uncertainty in the hazard assessment.
This broad-brush tsunami hazard assessment is intended to inform tsunami mitiga- tion strategies at the regional scale, and it is hoped that it will provide a foundation for more localized tsunami risk assessments to be undertaken in a systematic and consistent fashion across the Indian Ocean. Also, the uncertainty in the hazard assessment can serve as a guide to where further work is required to address the lack of data on historic and prehistoric tsunami. It should be appreciated, however, that the approach taken in this broad-brush assessment is not sufficient for understanding the tsunami threat at a commu- nity level, because the modelling is too coarse to accurately represent the tsunami heights on land that are needed to assess impact. While the assessment presented here can be used to determine what source zones contribute most to the hazard at a given coastal location, a proper assessment of the tsunami threat to a coastal community would require detailed inundation modelling for a range of scenarios to cover the most important source zones. Such modeling should be considered where this assessment suggests high hazard offshore a potentially vulnerable community, but the computational and data requirements for such modelling were well beyond the scope of this project."
information pertaining to earth sciences. Examples: geophysical features and processes, geology, minerals, sciences dealing with the composition, structure and origin of the earth s rocks, risks of earthquakes, volcanic activity, landslides, gravity information, soils, permafrost, hydrogeology, erosion