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Tsunami RiskMitigation Strategyfor Thailand
Kjell KarlsrudNorwegian Geotechnical Institute
(NGI)
This presentation gives:
• Brief review of causes and consequences
• Conclusions regarding future earthquake and tsunami risks
• Outline of proposed mitigation measures to reduce risks to an acceptable level
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Scope of the study• Identification of future tsunami-triggering
scenarios and associated hazard levels• Determine possible tsunami levels for the
various seismic scenarios• Assess future risk to human life• Propose mitigation measures to keep risk at
an acceptable level• Facilitate transfer of knowledge on local and
regional level
Regional seismicity and plate movements
From Lay et al. (2005)
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Plate movements in subduction zone
Tsunami definitions
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02468
101214
416500 417000 417500 418000 418500
East coordinate (UTM) [m]
Inun
datio
n le
vel [
m]
InundationLand elevation
Observed inundation- Bang Niang
Phang Nga
Kra
Phuket
Trang and Satuami affe cted areas Phi Phi Is lands
Zone 1
Zone 2
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Summary of consequences of 26 December 2004 tsunami
Nam Khem
Bang Niang
Patong4-7 m
7-12 m
6-8 m
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The earthquake of 26 Dec 2004 was the second largest since 1900
1. 1960 May 22, Southern Chile, M=9.52. 2004 Dec 26, Off west coast of N-Sumatra,
M=9.33. 1964 March 28, Prince William Sound,
Alaska, M=9.24. 1957 March 9, Andreanoff Islands Alaska,
M=9.15. 1952 Nov 4, Kamchatka M=9.0
Source: USGS
Future earthquake scenarios
• The energy released in the 2004 event means it will take several hundred years before a similar event can happen in the future
• It takes earthquake larger than M 8.0 to create tsunami of any significance, but not all will do so
• Largest credible earthquake in the next 100-200 years is M 8.5
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Tsunami modeling
• Back analyses of the 2004 event has given good match to observations
• A future M 8.5 earthquake will as an extreme cause 1.5-2.0 m inundationlevel
Extent of Dec.2004 seabed movements
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Calculated tsunami Dec.2004 at t=1 hr 20 min
-8-6-4-202468
10
0 1 2 3 4 5Time [hours]
Sur
face
ele
vatio
n [m
]
BangNiangPatong
Calculated tsunami Dec. 2004
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Seabed displacements for M 8.5 scenario
-1,5-1,0-0,50,00,51,01,52,0
1,5 2,0 2,5 3,0Time [hrs]
Sur
face
ele
vatio
n [m
]
H = 15.7mH = 27.2m
Calculated tsunami for M 8.5 event
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Future human risk in Thailand
1 10 1002 5 20 50 200 500Years after 26 December 2004
1E-006
1E-005
0.0001
0.001
0.01
0.1
1
10
100
Ris
k to
Hum
an L
ife
Acceptable
Tolerable
Unacceptable
Conservative risk estimate
Average risk estimate
Low risk estimate
Conclusions from risk assessment
• Within next 50-100 years maximum credible earthquake affecting Thailand is M 8.5 giving inundation level +2.5 to +3.0 at high tide.
Such tsunamis will give small consequences in ThailandNo immediate mitigation measures strictly necessary, but increased public awareness is desirable
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Conclusions from risk assessment• The potential for a new megathrust M 9+ event
will after 100-200 years give highly unacceptable risk
Potential for very large consequences, possibly even worse than 2004It should be the responsibility and duty of present generations to take steps to minimize consequences of such long term events
Qualifcations regarding other parts of the region
• A short to medium M 8.5 earthuake event couldhave worse consequences for Indonesia, Sri Lanka and India than for the west coast ofThailand
• The potential for M 9+ events on the subductionzone southwards from Banda Aceh represents a larger threat in short to medium term for Sumatra and areas further south
• Similar risk studies as carried out for Thailand are highly recommended
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Mitigation measures• The following types of measures have
been considered– enhanced public awareness– land use planning– site planning (elevating land, escape
routes)– improved building codes and design– physical barriers
• Warning systems are not specifically dealt with in this project
Specific recommendations for Thailand
• Within next few years implement measures to ensure lasting long term awareness
• Within next 5-10 years implement at leastsome physical measures to reduceconsequences of future tsunamis.
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How to ensure lasting awareness is a key issue
Case Patong City- masterplan
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Case - Bang Niang Resort-example of proposed site plan
Cross section- Bang Niang resort
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Modern version of Thai style house
Case Nam Khem fishing village
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Thank you for your attention!
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