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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

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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!