Download Risks of future Earthquake- and extreme hydrological

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
Email: [email protected]
URL: www.uni-kassel.de/fb14/geohydraulik/
5th NPRU conference, Nakhon Pathom, July 18-19, 2012
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 .
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
1.1 Introduction / Recent natural disasters in South East Asia /Thailand
2004 Aceh, Indonesia, Tsunami/ 285000 (8500 in Thailand) dead
Patong Beach
Propagation of
Tsunami wave
Aceh coast
1.1 Introduction / Recent natural disasters in South East Asia /Thailand
2006 Cyclon Nargis, Myanmar /140000 dead or missing
Eye of the Cyclon
Destruction in Rangoon
Area mostly affected
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
Extension of flooding
Bangkok flooding
1.2. Introduction: Statistics of natural disasters in Thailand, 1980-2010*
*Source: http://www.preventionweb.net
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).
2.1
Understanding geological hazards in SE-Asia / Geological hazard maps
Endodynamic: earthquakes and volcanoes
Exodynamic: landslides, debris flows
2.2
Understanding geological hazards in SE-Asia /
Earthquake intensity zones in SE- Asia
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
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
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
2.6
Understanding geological hazards in SE-Asia /
Earthquakes: magnitudes and intensities
Total energy release of
earthquakes between
1905 and 2006
Log E- relationship between earthquake
energy and its magniture
2.7
Understanding geological hazards in SE- Asia /
Earthquakes: Intensity risk zones SE-Asia
3. General concepts of hazard, vulnerability and risk
Risk
= P (hazard) * vulnerability
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.
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).
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
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 2001. 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
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
1) Magnitude
=> Seismic Hazard Curves:
2) Peak acceleration
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
5.1
Assessing seismic risk in Thailand / Seismicity
Tectonic setting and major faults
in SE Asia
5.1 Assessing seismic risk in Thailand / Seismicity
Seismicity of NE Indian Ocean 1900-2004
5.1 Assessing seismic risk in Thailand / Seismicity
Seismic Hazard in
SE Asia as related
to the Sumatra 2006
event
5.1 Assessing seismic risk in Thailand / Seismicity
Epicentral map of events in Thailand
1900-2006
(Palasri et al., 2006)
5.2 Assessing seismic risk in Thailand / Methods
Seismic Source
Gutenberg- Richter
5.2 Assessing seismic risk in Thailand / Methods
Attenuation model
Hazard probability
5.3 Assessing seismic risk in Thailand / Hazard probability maps
Example of seismic hazard probability map of Thailand (Palasri et al., 2006)
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
6.2
Aspects of risk assessment for dams / General approach
Flood wave from dam failure
(Arlai and Koch, 2009)
Risk analysis and risk evaluation for a dam
6.2
Aspects of risk assessment for dams / General approach
Contributing factors to dam failure
Statistics of dam failures
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.
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)
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
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
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 .
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.