Risks of future Earthquake- and extreme hydrological Disasters in Southeast Asia with a Focus on Thailand

Transcription

1 Risks of future Earthquake- and extreme hydrological Disasters in Southeast Asia with a Focus on Thailand Manfred Koch Department of Geohydraulics and Engineering Hydrology University of Kassel Germany kochm@uni-kassel.de URL: 5 th NPRU conference, Nakhon Pathom, July 18-19, 2012

2 Abstract Southeast Asia s risk of natural hazards is high, compounded by the rapid increas of the rate of urbanization, its proximity to seismically active faults and volcanic zones, its tsunamiprone coasts, and its susceptibility to the effects of extreme weather pattern and, not to the least to climate change. Since 2000, more than 100 million people in the region have been impacted by natural disasters. The region loses an estimated 0.3% of its GDP to disasters annually, with some countries incurring annual losses of up to 2 % of GDP. The two major natural disasters in the last decade are the 2004 Indian Ocean Tsunami and the 2008 Cyclone Nargis, which claimed lives of about four hundred thousand people and caused tens of billions in damages in an already impoverished region. While Thailand s risk to geological (earthquake) damage is relatively low, except at specific sites (dams), hydrological hazards through extreme weather events (monsoons, typhons, droughts) are recurring rather frequently, as witnessed by the 2008 drought and the 2011 floods, the latter affecting about 3 million people in central Thailand. Setting up appropriate risk mitigation management strategies presents an ongoing challenge for scientists and local authorities, and these must take into account the nature of a natural disaster. Thus geological hazards, which are nearly impossible to predict require other emergency measures than hydrological hazards which in many cases have some intrinsic lead times which could be wisely used to limit damages from the looming disaster.

3 Overview 1. Introduction 1.1 Some recent natural disasters in South East Asia /Thailand 1.2 Statistics of natural disasters in Thailand 1.3 Risks and damage of disasters world wide 2. Understanding geological hazards in SE Asia 3. General concepts of hazard, vulnerability and risk 4. Seismic hazard and risk 4.1 Overview 4.2. Effects 4.3 Quantification 5. Assessing seismic risk in Thailand 6. Aspects of risk assessment for dams 7. Evaluation of weather / hydrological risks 8. Conclusions

4 1.1 Introduction / Recent natural disasters in South East Asia /Thailand 2004 Aceh, Indonesia, Tsunami/ (8500 in Thailand) dead Patong Beach Aceh coast Propagation of Tsunami wave

5 1.1 Introduction / Recent natural disasters in South East Asia /Thailand 2006 Cyclon Nargis, Myanmar / dead or missing Eye of the Cyclon Area mostly affected Destruction in Rangoon

6 1.1 Introduction / Recent natural disasters in South East Asia /Thailand 2011 Thailand flood /1,425 billion baht (US$ 45.7 Bn) economic damages Ayutthaya flooding Bangkok flooding Extension of flooding

7 1.2. Introduction: Statistics of natural disasters in Thailand, * *Source:

8 1.3 Introduction: Risks and damage of disasters world wide 23 core global risks over a 10-year time frame estimated by World Economic Forum (2007).

9 2.1 Understanding geological hazards in SE-Asia / Geological hazard maps Endodynamic: earthquakes and volcanoes Exodynamic: landslides, debris flows

10 2.2 Understanding geological hazards in SE-Asia / Earthquake intensity zones in SE- Asia

11 2.3 Understanding geological hazards in SE-Asia / Plate tectonics and continental drift Tectonic plates with divergent and convergent plate boundaries, and active volcanoe Yearly average velocities of tectonic plates

12 2.4 Understanding geological hazards in SE-Asia / Plate tectonics: mid oceanic ridges and subduction zones Plate tectonic related geodynamic processes and the creation of divergent and convergent boundaries Ocean-ocean collision Ocean-continent collision

13 2.5 Understanding geological hazards in SE-Asia / Earthquakes: mechanisms and occurrence Strike slip fault Normal fault Delineation of earthquakes along a subduction zone Thrust fault

14 2.6 Understanding geological hazards in SE-Asia / Earthquakes: magnitudes and intensities Log E- relationship between earthquake energy and its magniture Total energy release of earthquakes between 1905 and 2006

15 2.7 Understanding geological hazards in SE- Asia / Earthquakes: Intensity risk zones SE-Asia

16 3. General concepts of hazard, vulnerability and risk Risk = P (hazard) * vulnerability

17 3. General concepts of hazard, vulnerability and risk Hazard and Risk are two fundamentally different concepts. Hazard is a phenomenon that has potential to cause harm. Phenomena are both natural and man-made. Earthquakes, hurricanes, tornadoes and floods are natural hazards; car crashes, chemical spills, train derailments, terror attacks are man-made Hazard is defined by two parameters: (1) a level of hazard (severity) and (2) its occurrence frequency, for example, a fatal car crash (severity) in every month and a magnitude 8 earthquake with a recurrence time of 500 years. Risk is the probability of harm if someone or something (vulnerability) is exposed to a hazard. Risk is defined by three parameters: (1) probability, (2) a level of hazard, and (3) exposure (time and asset). In health sciences, risk is defined as the probability of getting cancer if an average daily dose of a hazardous substance is taken over a 70-year lifetime.

18 4.1 Seismic hazard and risk / Overview Seismic Hazard: Earthquakes of a certain magnitude or phenomena generated by the earthquakes, such as - surface rupture, - ground motion - ground-motion amplication - liquefaction, and - induced landslides that have potential to cause harm and the associated occurrence frequencies. Seismic Risk: Probability of experiencing a level of seismic hazard for a given exposure (time and asset).

19 4.2 Seismic hazard and risk / Effects Ground Motion Most damage during an earthquake is caused by ground motion, measured by peak ground acceleration ( PGA ), expressed as a percentage of the acceleration of g. The larger an earthquake's magnitude, the stronger the ground motion it generates. Level of ground motion at a site depends on distance from the epicenter. Ground- motion amplification Local geology and soil also play important roles in earthquake damage. Soft soils overlying hard bedrock tend to amplify the ground motions -- known as ground-motion amplification which can cause excess damage, even far away from the epicenter such as in Mexico City (Fig.) during the 1985 earthquake or in San Francisco during the 1989 Loma Prieta earthquake

20 4.2 Seismic hazard and risk / Effects Liquefaction Soft sandy soils can be liquefied by strong ground motion liquefaction. Liquefaction can result in foundation failure. Figure shows that sandy soil was liquefied and behaved like fluid during the Nisqually, Washington, earthquake in Many communities in river valleys are set on soft soils and are prone to liquefaction hazards Earthquake-induced landslides Strong ground motion can also trigger landslides in areas with steep slopes. Figure shows slope failure by the Nisqually earthquake in Kentucky in 2001

21 4.3 Seismic hazard and risk / Quantification Relationship between seismic hazard and risk is complicated and must be treated very cautiously. Seismic hazards are natural occurrences and can be evaluated from instrumental, historical, and geological records (or observations) and expressed in terms of - a level of hazard and - its occurrence frequency => Seismic Hazard Curves: 1) Magnitude 2) Peak acceleration

22 4.3 Seismic hazard and risk / Quantification Seismic hazards are commonly assessed either by 1. probabilistic seismic hazard analysis (PSHA) or 2. deterministic seismic hazard analysis (DSHA). The fundamental difference between PSHA and DSHA is in how the uncertainties are treated: either implicitly (PSHA) or explicitly (DSHA). PSHA has been more widely used, but has some intrinsic drawbacks

23 5.1 Assessing seismic risk in Thailand / Seismicity Tectonic setting and major faults in SE Asia

24 5.1 Assessing seismic risk in Thailand / Seismicity Seismicity of NE Indian Ocean

25 5.1 Assessing seismic risk in Thailand / Seismicity Seismic Hazard in SE Asia as related to the Sumatra 2006 event

26 5.1 Assessing seismic risk in Thailand / Seismicity Epicentral map of events in Thailand (Palasri et al., 2006)

27 5.2 Assessing seismic risk in Thailand / Methods Seismic Source Gutenberg- Richter

28 5.2 Assessing seismic risk in Thailand / Methods Attenuation model Hazard probability

29 5.3 Assessing seismic risk in Thailand / Hazard probability maps Example of seismic hazard probability map of Thailand (Palasri et al., 2006)

30 6.2 Aspects of risk assessment for dams / Thailand situation Srinakarind dam data Seimics fault zones in western Thailand and location of the Srinakarind dam

31 6.2 Aspects of risk assessment for dams / General approach Risk analysis and risk evaluation for a dam Flood wave from dam failure (Arlai and Koch, 2009)

32 6.2 Aspects of risk assessment for dams / General approach Contributing factors to dam failure Statistics of dam failures

33 6.3 Aspects of risk assessment for dams / Effects of earthquakes Earthquakes have often caused cracks or settlement, but have caused few failures of dams more than 15 m high. The consequences of earthquakes may be: - Sudden failure, for instance by liquefaction of fine non-cohesive materials or structural failure of buttresses. - Cracks which may continue to extend hours or days later, particularly in the case of masonry dams or old fill dams with no filters or drainage. - Generation of landslides upstream of dam, leading to large (Tsunami-like) waves in reservoir => Overtopping => Breaching => Dambreaking flood wave Though the yearly failure probability of dams is lower than 10-6 in most cases, it may be in the range of 10-3 for some dams in seismic areas. Seismic risk assessment is less precise than for floods and emergency planning is less effective. More expensive structural measures may be necessary.

34 6.4 Aspects of risk assessment for dams / Simulation of dam breaking waves and delineation of flood maps Simulation of the movement of a flood wave in the Chao Phraya river in year 2006 Flood retention reservoir and Chayo Phraya dam Simulation of water levels during the downstream movement of the flood along the Chao Phraya river in year 2006 (Arlai and Koch, 2009; 2010)

35 7. Evaluation of weather hydrological risks / SE- Asia / Ocean states Because of the location of SE-Asia and Thailand between the Pacific and the Indian Ocean, the region s local climate and its surface water resources are strongly influenced by monsoon seasons and other multi-seasonal weather pattern which, in turn, depend upon the thermal states of the oceans. => Understanding teleconnections from the oceans with regional climate indices allows short-range climate predictions in the area (Bejranonda and Koch, 2013) Pacific and Indian ocean indices that act as teleconnectors for local climate variables in SE-Asia. ENSO / SOI- (El Nino-Southern Oscillation Index) time series Current (La Nina) SST conditions SST-anomalies for El Nino and La Nina conditions

36 7. Evaluation of weather / hydrological risks / SE- Asia / El Nino /La Nina ocean teleconnections Weather conditions around the Pacific Ocean during La Nina conditions Weather conditions around the Pacific Ocean during El Nino conditions

37 8. Conclusions Compared with other regions on the earth, Southeast Asia s risk of natural hazards is very high due to rapid increase of rate of urbanization, its proximity to seismically active faults existence of active volcanic zones tsunami-prone coasts susceptibility to the effects of extreme weathers and climate change Natural disasters are either of geological nature (endodynamic or exodynamic) or of meteorological / hydrological origins The high geological disaster risk in SE Asia is related to the peculiar geodynamic situation of the region as part of circum-pacific ring with active plate tectonic processes => Evaluation of these risks, namely, seismic risk is very difficult, if not impossible Thailand s risk situation low with regard to geological (earthquake) hazard, except at specific sites (dams) high with regrad to hydrological hazards through extreme weathers (monsoons, typhons, droughts) Risk mitigation management strategies must take into account the nature of a natural disaster geological hazards reduction requires appropriate engineering measures to reduce vulnerability. hydrological hazards in the region related strongly to hemi-spherical weather pattern and ocean state indices (EL NINO, LA NINA) => intrinsic seasonal lead times can be used to some extent for taking preemptive measures to limit damages from looming disaster.

38 8. Conclusions / continued Specific considerations for risk analysis for dams Concern among practitioners that risk analyses are too subjective, do not have clear-cut procedures for calculating failure probabilities, and have too much reliance on expert judgment. Recommendations and questions addressed by experts: - Additional refinement of quantitative analyses. - Development of internal erosion analysis methods to be used in a risk analysis format. - Retrospective probability of failure under static loading. - Whether societal risk criteria should be applied on a total expected annual risk to life basis or on a specific event basis. - The concept of average individual risk over the population risk. - Prediction of loss of life. - Whether upgrading of dams should have the same criteria applied as for new dams. - Forestalling vulnerability and risk from dam breaking waves by using modern modeling software to predict lead times and to map flood zone areas.