Tsunami Risk Reduction Measures Phase 2 November 2009 Cover pictures; Initial water displacements (m) for the Seismicity of the study region for 1963- three northernmost Sunda Arc scenarios 2006, with symbols differentiating the of magnitude M 8.55, 8.53 and 8.60 magnitudes. respectively, as well as the M 8.86 Burma fault scenario. Merged tsunami hazard Merged tsunami hazard Merged tsunami hazard map for Sri Lanka. map for the Philippines map for Eastern Indonesia The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the CCOP Technical Secretariat concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Note: The conclusions and recommendations of this publication have not been specifically endorsed by, or reflect the views of the organizations which have supported the production of this project, both financially and with content. © Coordinating Committee for Geosciences Programmes in East and Southeast Asia, 2009 Document No.: 20061179-00-227-R Date: 2009-11-06 Page: 3 Project Project: Tsunami Risk Reduction Measures phase 2 Document No.: 20061179-00-227-R Document title: Tsunami Risk evaluations for Indonesia Date: 6 November 2009 Client Client: CCOP Technical Secretariat Client’s contact person: Niran Chaimanee Contract reference: Contract between CCOP and NGI of 17. April 2008 For NGI Project manager: Kjell Karlsrud Prepared by: Bjørn Kalsnes Finn Løvholt, Sylfest Glimsdal, Daniela Kühn, Hilmar Bungum, Helge Smebye Reviewed by: Carl Bonnevie Harbitz Summary This report presents tsunami hazard analyses dedicated to the coastlines of eastern Indonesia. Available seismic and tsunami catalogues indicate that there is a high level of seismicity the last 100 years and a large number of historical tsunamis within the last 300-400 years. It is clear that the main areas of tsunami generation are located close to the major fault zones. The database shows that a large number of tsunamis have occurred in eastern Indonesia, and that the sources are distributed to many regions. Even so, most other efforts on tsunami simulations and tsunami warnings nowadays are focusing on western Sumatra and Southern Java. Document No.: 20061179-00-227-R Date: 2009-11-06 Page: 4 In agreement with the Center for Volcanology and Geological Hazard Mitigation in Indonesia (CVGHM), the hazard was studied within four regions of eastern Indonesia (Bali/Flores, the Banda Sea, North Sulawesi, and Irian Jaya). Tsunami hazard maps for earthquake generated tsunamis are developed by applying numerical simulations for a total of eleven ‘credible worst case scenarios’. In addition, one landslide generated tsunami scenario for Ceram Island is conducted for demonstration purposes. Return periods for the individual earthquake scenarios are not quantified. Lower bound return periods for the earthquake magnitudes comparable to the scenarios are found within some of the study regions, with the shortest periods 30-40 years obtained from the regional seismicity. However, the scenario return periods are believed to be a few times longer than the lower bound. The tectonic convergence rates support higher return periods of 100-1000 years for the scenario magnitudes in question. It is noted that the scenarios investigated are considered worst case with respect to both strength and location, and it is assumed that they will contribute to a large part of the total risk compared to smaller scenarios. Figure 1: Merged regional tsunami hazard map for parts of eastern Indonesia. High population density is visualised using the global GRUMP dataset, with dark colours indicating high density. A tsunami hazard map obtained by combining the results for all the different study regions is shown in Figure 1. The map clearly shows that large parts of eastern Indonesia may be subject to tsunami maximum water level of several meters, and in some areas more than 10 m. It is emphasized that this region is an extremely complex region tectonics wise, and that a great amount of work remains before a Document No.: 20061179-00-227-R Date: 2009-11-06 Page: 5 more solid understanding of tsunami generation and its underlying sources can be achieved. It should also be kept in mind that the present scenarios do not give a full coverage of all the possible ‘worst case scenarios’ that could occur in this region, even though the ones contributing most to the hazard are included. It is important to note also that tsunamis generated by landslides and volcanoes are not included in the hazard map, as well as earthquake sources in areas like Southwest Sulawesi, Halmahera, the southern part of the Banda Sea, as well as transpacific events. Therefore, if any such additional sources are considered to be as likely as the ones included, additional calculations should be performed, and added to the merged hazard map in the future. It is emphasized that only regional inundation maps are produced. The need for additional local inundation analyses should be assessed for exposed locations. The present study is limited in size and depth and the results should therefore be considered as preliminary. However, even a larger study of this kind would be uncertain, due to the fact that all such studies are based on prediction of future events. Even so, much knowledge of societal importance is now available from the present study and should be put into action. Contents Document No.: 20061179-00-227-R Date: 2009-11-06 Page: 6 1 Introduction 7 2 Definitions 8 3 Historic background and definitions of study areas 10 4 Results for each study region 13 4.1 Bali and Flores Sea region – Nusa Tenggara 13 4.2 Banda Sea and the Moluccas 18 4.3 Northern Sulawesi 23 4.4 Irian Jaya 27 4.5 South West Mindanao – Cotabato Trench 30 4.6 Demonstration of the modelling of landslide generated tsunamis – a case study for Ceram Island 33 5 Merged hazard maps and input to regional hazard assessment 37 5.1 Use of the merged hazard map – applications for local hazard mapping 39 6 Acknowledgements 42 7 References 42 Review and reference page Document No.: 20061179-00-227-R Date: 2009-11-06 Page: 7 1 Introduction The project “Tsunami Risk Assessment and mitigation in S&SE Asia – Phase 2” has been financed by The Norwegian Ministry of Foreign Affairs (MFA). The Coordinating Committee for Geoscience Programmes in East and Southeast Asia (CCOP), through their Technical Secretariat in Bangkok, acted as the project responsible institution towards MFA. The Norwegian Geotechnical Institute (NGI) had the role as Technical Executing Organisation (TEO). NGI subcontracted NORSAR for performing the seismological analyses required. The project was contracted in 2008 with four Asian countries: Indonesia, the Philippines, Vietnam, and Sri Lanka. The main goals of the project have been to reduce the tsunami risk in South and Southeast Asia by: • Enhanced assessment of tsunami hazard and recommendations of risk mitigation measures in specified regions • Enhanced capacities of hazard assessment and risk reduction for regional, national, and local institutions The detailed scope of work (SoW) for the invited countries the Philippines, Indonesia, Vietnam, and Sri Lanka varied according to the needs defined from previous tsunami hazard assessments and the capabilities of the individual countries. The SoW’s were agreed in project meetings with the countries in the early phase of the project. A map of the study area is shown in Figure 2. This report presents tsunami hazard analyses dedicated to large parts of eastern Indonesia. In the complete project report (NGI, 2009) findings for all the four countries and more elaborate details of the analyses relevant for eastern Indonesia are given. For this purpose, NGI (2009) is extensively cited herein. Historical tsunamis and earthquakes were investigated using available catalogues. A regional tsunami database was established, indicating that there is a high level of seismicity the last 100 years and a large number of historical tsunamis within the last 300-400 years. It is clear that the main areas of tsunami generation are located close to the major fault zones. The database shows that a large number of tsunamis have occurred in eastern Indonesia and the Philippines, and that the sources are distributed over many regions. Even so, most other efforts on tsunami simulations and tsunami warnings are nowadays focusing on the western part of the Sunda Arc, from the Andaman Islands to southern Java. It is emphasised that the hazard evaluations in this report considers only potential tsunamis of seismic origin. Modelling of tsunamis generated by landslides is included for demonstration purposes only. Moreover, it is stressed that a scenario based approach rather than a full probabilistic method is applied in this report. Document No.: 20061179-00-227-R Date: 2009-11-06 Page: 8 Figure 2: Map of the study area including Indonesia, the Philippines, Vietnam, and Sri Lanka. 2 Definitions Below, some definitions of technical key terms used in this text are given to help the reader. As far as possible, compatibility with the UNESCO-IOC tsunami glossary (UNESCO-IOC, 2006) is endeavoured. In addition, a brief definition sketch defining the parameters related to the tsunami inundation process is given in Figure 3. • Fault - A fracture or a zone of fractures along which displacement has occurred parallel to the fracture. Earthquakes are caused by a sudden rupture along a fault or fault system; the ruptured area may be up to several thousand square kilometers. Relative movements across a fault may typically be tens of centimeters for magnitude 6.0-6.5 earthquakes, several meters for magnitude 7-9 earthquakes. • Flow depth – Water elevation above land during inundation. • Hazard - Probability that a particular danger (threat) occurs within a given period of time.