Tsunamis - Universitetet i oslo€¦ · Tsunamis are long waves (wavelength λ>> water depth h) Unidirectional motion implies constant wave period T Wave period T = λ/c ⇒λ~ c

Tsunamis

GEO 4180 - Mitigation for Geohazards, UiO, October 27, 2008

Bjørn Vidar Vangelsten

Contributions from:Finn Løvholt1,2

Carl Harbitz 1,2

Sylfest Glimsdal1,2

Geir Pedersen1,3

Kjell Karlsrud2

1 ICG – International Centre for Geohazards 2 NGI – Norwegian Geotechnical Institute3 UiO – University of Oslo, Dept. of Mathematics

Contents

1. Introduction and basics2. Historical events3. Tsunami wave theory4. Case studies and impact5. Mitigation6. Information sources Simulation of hypothetical wave

generated off Sumatra

1. Introduction and basics


What is a tsunami?Definition:• Unusually large wave in a harbour (Japanese)• Wave generated by huge and

sudden perturbation (e.g. earthquakes, slides, volcanoes, asteroids)

Characteristics:• Wave period: 2-200 minutes• Initial wave height:

• Submarine slides, earthquakes O(1-10 m)

• Rockslides O(10-100 m)

• Run-up heights spans from centimeters to hundreds of meters


Basics of tsunami waves


Wave propagation speed in different phenomena

• Light, 300000 km/s

• Sound(air) 340 m/s

• Sound(water) 500 m/s

• Seismic waves 100-7000 m/s

• Ocean waves < 315 m/s

Speed:Type:


A rough classification of different ocean waves

12-24 hours1000-10000 (km)15Tidal wave

6-12 hours500-2000 (km)5Storm surge

1-15 min1-100 (km)100Tsunami

13-30 s0.1-1 (km)8Swell

0.1-20 s0.1-500 (m)25Wind waves

PeriodWave lengthMax height (m)


Tsunami shoaling in the open sea typical data for the 2004 Indian Ocean Tsunami


2. Historical events

http://gogreece.about.com/library/blsantoriniphoto-1.htm

http://gogreece.about.com/library/blsantoriniphoto-1.htm

Tsunami deposits on Santorini


(courtesy, S. Tinti, Univ. of Bologna)

Examples of historical events in Europe 2. Historical even

> M 8.5M 8.0-8.5

M 7.5-8.0< M 7.5

Volcanoes +Landslides +Unknown/other

* No magnitude

Location of past tsunamigenic sources in South East Asia

Earthquakes, landslides and volcanoes


> 1000100-100050-100

1-50

Fatalities for past events in South East Asia (sourcelocations)


3. Tsunami wave theory

3. Tsunami Wave Theory

Tsunamis are long waves (wavelength λ >> water depth h)

Unidirectional motion implies constant wave period TWave period T = λ/c ⇒ λ ~ c ~h½

Wave energy ~ a2 λ ⇒ a ~ λ-½ ~ h-1/4

Volume flux over a wave period: QT~ uhT ~ aλ ⇒ u ~ h-3/4

c

h

a

u

Height increases and length decreases in shallow water Shoaling

Wave propagation speedc = (gh)1/2


Tsunami Wave Theory

Characteristic waveform during tsunami generation from an earthquake in a subduction zone – dip slip dominant in wave generation


Characteristic wave pattern generated by a submarine slide dipole

The observer will first see a withdrawal of the sea surface


c

h

a

u

Importance of depth on generation, earthquake versus slide

• Earthquake• Initial wave length independent of depth• Initial period• Waves steeper from deep to shallow water• Seabed displacement in deep water most dangerous

• Submarine slide• Wave speed higher in deep water• Less critical ⇒ initial wave heights smaller• Larger area for radial damping• Release in deep water least dangerous

2/1−∝hT


Shallow water approximation• Waves long compared to the depth (generally λ > 20 h)• In large depths small amplitude wave speed c = (gh)1/2

• Smaller depths steepening and eventually breaking• Most used approximation for tsunami modeling • Often valid for tsunamis generated by large earthquakes

c

h

a

u

λ


Courtesy:

Geir Pedersen, UiO

Full process, generation, propagation, dispersion, amplification and bore formation


Inundation and run-up


Inundation profiles and definitions –sketch from Thailand

Equilibrium water depth

Maximum waveMaximum inundation height

Maximum inundation height

Inundation length

Run-upheight

Typical feature for long waveRun-up < Maximum inundationFriction reduces the flow height

Flowheight


4. Selected case studies

4. Case studies and impact

1. The Storegga slide (Trigger: Sub marine slide)2. Tafjord 1934 (Trigger: Rock slide into fjord)3. Mjølnir (Trigger: Asteroid impact)4. The Indian Ocean tsunami 26 December 2004

(Trigger: Earthquake)

The tsunami from the 8200 BP Storegga slide, Western Norway

> 10 m

> 20 m

3-6 m

3-5 m

9-10 m10-12 m

6-7 m

Storegga tsunami deposits Run-up of tsunami deposits

StoreggaSlide

Fig. 1

Volume: 2400 km3

Max speed: 35 m/s

Run-out distance: 150 km


Numerical simulation of the tsunami generated by the Holocene Storegga slide, 8150 BP

Copyright 1995, University of Oslo, Dept. of Math.

NNorway

Iceland

Scotland


• Tafjord 1934, western Norway

• 2-3 mill. m3

• Max run-up 62 m• 41 perished

Rockslide impacts4. Case studies and impact

Copyright 1995, University of Oslo, Dept. of Math.


Mjølnir asteroidimpact

• Barents Sea (N73, E29)• 142 mill. years ago• Diameter of crater:

40 km• Assumed diameter of asteorid: 1.5

km• Impact velocity: 20 km/s• Sea depth: 400 m• Direction:

from south/south-east

Reconstruction of Paleo Barents Sea by Dypvik et al.


The 2004 Indian Ocean tsunami

From Krueger & Ohrnberger (2005)


M=9.3; t=60 minM=9.3; t=40 minM=9.3; t=80 minM=9.3; t=20 minM=9.3; t=100 minM=9.3; t=120 min

Back-calculations of the26. December 2004 M=9.3 event (LSW)


Impact of the 2004 Indian Ocean tsunami

• Devastated large areas along the coastlines of Indonesia, Thailand, Malaysia, Myanmar, Sri Lanka, India, the Maldives and even some parts of the east African coast.

• It caused of the order of 220,000 casualties,

• whereof about 8,000 along the coasts of Thailand.


Three example areas in Thailand

• Nam Khem fishing village:

• Bang Niang tourist resort area

• Patong City


Patong City4. Case studies and impact

• Located within a 3-4 km long and 3-4 km wide bay. • The number of casualties was 160 out of the approximately 20,000 people that were in

the city when the tsunami struck. Most casualties were caused by people who could not escape from the basement floor in a shopping store.

• Natural ground level typically + 3 m above sea level. • The tsunami inundation level was +5 m to +6 m• For buildings facing the sea/beachfront located typically 50 m from the sea, most brick

walls, plaster walls, windows and doors facing the sea were blown out by the tsunami wave.

• The buildings did not collapse because they had load carrying concrete columns that remained intact.

Bang Niang tourist resort area

• stretches about 12 km north of Khao Lak. • In this area the tsunami inundation level was generally around +10 m, but locally up to + 12

m near the beachfront. • The natural ground level behind the beachfront typically lies at +4 m to +5 m. The resorts

consisted mainly of 2 to 3 storey buildings. • The tsunami wave smashed through both the 1st and 2nd floors of the buildings, and on its

way blew out most brick and plaster walls both at front, back and the sides of most buildings within 500 m distance from the sea.

• Even in Bang Niang relatively few buildings collapsed completely because they had reinforced concrete columns that were able to carry the loads, though the walls were being blown out by the tsunami impact

• There were about 100 resorts in the Bang Niang area with about 15,000 present when the tsunami wave struck,

• About 3000 people lost their lives.


Nam Khem fishing village • Tsunami inundation level was +8 m. • The ground level in most of the village lies at +3

m to +6 m. • The houses consisted for the most part of rather

simple 1-2 storey brick structures without solid columns.

• 4800 people lived in the village whereof 3000, or approximately two-thirds of the population, lost their lives in the tsunami.’

• This is, relatively speaking much more than in the Bang Niang tourist resort area, which may be explained by the following factors:

• Many people were at the fishing harbour at the seafront, and were killed by debris from wharf structures and boats that were thrown around by the tsunami wave.

• Many buildings collapsed completely due to poor quality and lack of solid columns to support the structure.

• The main roads in the area were running more or less parallel to the waterfront giving long or difficult escape paths to safer high areas inland.

• A number of mining ponds are located in the village. These ponds in themselves represented a hazard when the tsunami hit, as people were flushed into these ponds where it was even more difficult to save oneself.


5. Mitigation

5. Mitigation

Critical elements of preparedness (Source: UNESCO-IOC, 2008, TsunamiTeacher)

5. Mitigation

High level advocacy ensures a sustained commitment to prepare for infrequent, high-fatality natural disasters such as tsunamis.High level advocacy8

Stakeholder coordination is the essential mechanism that facilities effective warning and emergency response actions. Clear designation of the national or local authority from which the public will receive emergency information is critical to avoid public confusion, which compromises public safety.

Stakeholder coordination

7

Strong buildings, safe structures and prudent landuse policies save lives and reduce property damage, when implemented as pre-disaster mitigations. Tall, reinforced- concrete buildings may be adequate places to which people can vertically evacuate if there is no time or too dense a population to reach higher ground inland. Long term planning to avoid placing critical infrastructure and lifeline support facilities in inundation zones will also reduce the time needed for services to be restored.

Strong buildings, safe structures, wise land use

6

Planning activities identify and create public safety procedures and products, and build capacity for people and organizations to respond quickly. It is necessary to create and widely disseminate tsunami evacuation and flooding maps, and instructions on when, where and how evacuate. Shelters and evacuation routes need to be clearly identified, and widely known by all segments of the coastal population.

Planning activities5

Preparedness activities educate and inform a wide populace, including government responders and people providing lifeline and critical infrastructure services, on the procedures and actions that must be taken to ensure public safety. Drills and exercises before an event, and proactive outreach and awareness activities, are essential to reducing tsunami impacts.

Preparednessactivities

4

Awareness activities enable ordinary citizens to recognize a tsunami and know what to do. Citizens should be able to recognize a tsunami’s natural warning signs and respond immediately. This is especially the case for local tsunamis, which may hit within minutes and before an official tsunami warning can reach communities.

Awareness activities3

Warning systems reliably inform vulnerable populations immediately and in an understandable, culturally appropriate way. A Warning Centre must be able to analyze and forecast the impact of a tsunami on coasts, ahead of its arrival. Local, regional and-or National Disaster Management Organizations must be able to immediately disseminate information on the threat, and to enable the evacuation of all vulnerable communities. Communications methods must be reliable and robust, and work closely with the mass media and telecommunications providers to get broadcasts out fast.

Warning systems2

Proper instruments enable the early detection of potentially harmful earthquakes and tsunamis. The data obtained by these instruments must be readily available to all nations continuously and in real-time to be effective.

Proper instruments1

ExplanationElement ofpreparedness

No

Designing for tsunamis: seven principles for planning and designing for tsunami hazards (Source: Eisner 2005: National Tsunami Hazard Mitigation Program)

Plan for evacuation7

Take special precautions in locating and designing infrastructure and critical facilities to minimize tsunami damage

6

Protect existing development from tsunami losses through redevelopment, retrofit, and land reuse plans and projects

5

Design and construct new buildings to minimize tsunami damage4

Locate and configure new development that occurs in tsunami run-up areas to minimize future tsunami losses

3

Avoid new development in tsunami run-up areas to minimize future tsunami losses2

Know your community’s tsunami risk, hazard, vulnerability and exposure1

PrinciplePrinciple No

5. Mitigation

Goals for a tsunami resistant community(Source: Dengler, 1998: Strategic Implementation Plan for Tsunami Mitigation Projects from the National Tsunami Hazard Mitigation Program)

• Understands the nature of the tsunami hazard1. Tsunami inundation map guidance. 2. Guidance for regions without inundation maps. 3. Knowledge of the past impact of tsunami events.

• Has the tools it needs to mitigate the tsunami risk1. Identify needed mitigation tools. 2. Tool Development. 3. Dissemination.

• Disseminates information about the tsunami hazard1. Identify vulnerable populations. 2. Materials for identified populations. 3. Dissemination mechanism.

• Exchanges information with other at-risk areas1. Resource Center for tsunami mitigation. 2. Workshops and meetings. 3. Annual Report of Mitigation Projects.

• Institutionalizes planning for a tsunami disaster.1. Identify existing hazard mitigation programs. 2. Establish state and/or local tsunami work groups. 3. Develop state tsunami mitigation plans. 4. Reward innovation in tsunami mitigation.

5. Mitigation

Situation on the ground:During 2005, assessments of 16 countries in the Indian Ocean were conducted by teams of national and international experts to identify capacity building needs and support requirements for developing a tsunami warning system. The team’s comprehensive investigations found, in summary, that overall in the region much progress had been made – but much also remained to be done:

1. Disaster management laws specifically addressing tsunami coordination: Most countries had established or strengthened disaster management laws, national platforms, and coordination mechanisms to guide all-hazard disaster risk reduction. Not all had specifically addressed the tsunami coordination aspect.

2. Few countries able to receive or provide real-time seismic or sea level data: All countries except Somalia were receiving tsunami advisories and watch alerts on an interim basis from warning systems in the United States and Japan, and most had facilities able to receive warnings around the clock. But few operated a national warning centre or were able to receive or provide real time seismic or sea level data.

3. Information needed to develop plans, yet to be collected: Few countries had developed tsunami emergency and evacuation plans and signage or tested response procedures for tsunamis or earthquakes. Much of the information needed to develop these plans, such as post-event surveys, inundation modeling, and tsunami hazard and vulnerability assessment, has yet to be collected.

4. Community education programmes developed but not in place: Many countries had assessed local government capacity for disaster preparedness and emergency response but not community preparedness. Community education and outreach programmes were being developed but were largely not in place.

5. Local planning activities carried out first in target areas rather than as comprehensive national programmes: Most countries had made progress developing policies, assessing technological needs, and setting up national coordination mechanisms for warning and mitigation. But local planning and preparedness activities were being carried out first in target areas, or cities and towns, rather than as comprehensive national programmes.

Source: TsunamiTeacher

5. Mitigation

DART Buoy

Courtesy – L. Iniss, Caribbean EWS

Tsunami warning system -The Dart system

5. Mitigation

Element No 1: Proper instruments

SEISMIC STATIONSTsunami warning system –Seismic monitoring stations

Source: TsunamiTeacher

5. Mitigation

Element No 1: Proper instruments

Tsunami warning systems (Source: TsunamiTeacher and Web-Page of GeoForschungsZentrum Potsdam)

• Existing warning systems: The development of the Pacific Tsunami Warning and Mitigation System, including technologies used for tsunami detection, and of the Japan National Tsunami Warning System as a warning system for local tsunamis.

• New warning systems: The evolving Indian Ocean Tsunami Warning and Mitigation System as an international warning system for basin-wide tsunamis, and the capacity needed to develop systems that cover all regions

• Development of a global warning system out of existing and emerging regional tsunami warning systems, and the necessary characteristics of sustainable tsunami detection, warning and operational centres

International efforts to mitigate the effect of tsunamis, coordinated through the UNESCO Intergovernmental Oceanographic Commission (IOC):

5. Mitigation

Element No 2: Warning systems

Tsunami warning systems (Source: TsunamiTeacher)

5. Mitigation

Element Nos 2, 3, 4: Warning systems, awareness activities, preparedness activities

Mobile artificial earthquake facility for awareness creationSource: Edward et. al. 2006)

5. Mitigation

Element No 3: Awareness activities

Oki beach and its vicinity, Japan, including the coastal forest.

Local hazard map - tsunami run-up – example from Åfjorden Western Norway

5. Mitigation

Element No 5: Planning activities

Inundation maps for different return periods• Robust numerical tools are now

becoming available• Empirical and statistical data

should also be considered

Example Oregon, US (Gonzales, 2005)• Wave propagation and inundation

modelling using nested grids • Detailed hazard maps for 100 and 500

year tsunamis were established

5. Mitigation

Element No 5: Planning activities

Old and new evacuation pathway in Kushimoto Town, Japan, shortening evacuation time from 15 to 6 minutes (ADRC, 2007)Source: Edward et. al. 2006)

5. Mitigation


Element Nos 5, 6: Planning activities, Strong buildings, safe structures, wise land use

Landscaping as means for improving tsunami safety5. Mitigation

Element Nos 5, 6: Planning activities, Strong buildings, safe structures, wise land use


Coastal forests to protect from storms and tsunamis Source: Edward et. al. 2006)

5. Mitigation

Element No 6: Strong buildings, safe structures, wise land use


Breakwater in Ofunato bay, Japan Source: Edward et. al. 2006)

5. Mitigation



Evacuation facility in Irino beach, Japan Source: Edward et. al. 2006)

5. Mitigation



6. Information sources on tsunami and mitigation

6. Information sources on tsunami and mitigation,1 of 2Andjelkovic, Ivan (2001): Guidelines on non-structural measures in urban flood management. IHP-V Techical Documents in Hydrology no.50, UNESCO Paris. http://www.wwf.pl/powodz/publikacje/UNESCO%20report.pdf

Asian Disaster Reduction Center, ADRC (2005): Total Disaster Risk Management - Good Practices 2005, http://www.adrc.or.jp/publications/TDRM2005/TDRM_Good_Practices/GP2005_e.html



Dengler, L. (1998): Strategic Implementation Plan for Tsunami Mitigation Projects, NOAA Technical MemorandumERL PMEL-113, October 1998, http://www.pmel.noaa.gov/pubs/PDF/deng2030/deng2030.pdf

Edward, J. K. P., Terazaki, M. and Yamaguchi M. (2006): The impact of tsunami in coastal areas: Coastal protection and disaster prevention measures—Experiences from Japanese coasts, Coastal Marine Science 30(2): 414–424, 2006, http://www.sdmri.org/reports/Impact%20of%20Tsunami%20in%20Coastal%20Areas%20-%20Coastal%20Protection%20and%20Disaster%20Prevention%20Measures.pdf

Eisner, R., K. (2005): Planning for Tsunami: Reducing Future Losses Through Mitigation, Natural Hazards (2005) 35: 155–162

Federal Emergency Management Agency (FEMA) (2000): Coastal Construction Manual – Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Building in Coastal Areas. 3rd ed., 3 vol. (FEMA 55), Washington D.C.

Government of India, Ministry of Home Affairs, National Disaster Management Division (2005): Prevention/Protection and Mitigation from Risk of Tsunami Disasters - A Concept Note, March 2005. http://www.reliefweb.int/rw/lib.nsf/db900sid/RMOI-6B99NU/$file/govind-ind-mar.pdf?openelement

6. Information sources on tsunami and mitigation

6. Information sources on tsunami and mitigation,2 of 2Govt of Japan (2008): Sharing Japan's Experience in Natural Disasters, http://www.adrc.or.jp/publications/Japan_Good_Practices/index.htm

MLIT (Ministry of Land, Infrastructure, Transport and Tourism, Ports and Harbours Bureau), 2006): Upgrades of protection functions against tsunami, storm surge, etc., http://www.mlit.go.jp/english/2006/k_port_and_harbors_bureau/09_tsunami/index.html

NSTC (National Science and Technology Council, December 2005): Tsunami risk reduction for the United States: A framework for action, http://nthmp.tsunami.gov/A_Framework_for_Action-2005-12-22.pdf

NTHMP (National Tsunami Hazard Mitigation Program, 2001a): Designing for Tsunamis. Seven Principles for Planning and Designing for Tsunami Hazards. http://www.oes.ca.gov/Operational/OESHome.nsf/PDF/Tsunamis,%20Designing%20for%20/$file/DesignForTsunamis.pdf

NTHMP (National Tsunami Hazard Mitigation Program, 2001b): Designing for Tsunamis. Background Papers.http://www.pmel.noaa.gov/tsunami-hazard/BackgroundPapersintrochpts1-2.pdf

NGI (2006): Tsunami Risk Reduction Measures with Focus on Land use and Rehabilitation, Main Report, NGI report 20051267-1, 14 January 2006

Ohta, Hideki, Thirapong Pipatpongsa and Tory Omori (2005): Public education of tsunami disaster mitigation and rehabilitation performed in Japanese primary schools. Paper to the International Conference on Geotechnical Engineering for Disaster Mitigation & RehabilitationUnited Nations Development Programme, UNDP (2008): Human Development Report 2007/2008, http://hdr.undp.org/en/reports/global/hdr2007-2008/

UN-ISDR (2002). Natural Disasters and Sustainable Development: understanding the links between development, environment and naturaldisasters, http://www.unisdr.org/ppew/whats-ew/pdf/wssdisdrdoc.pdf

UNESCO-IOC (2005). Intergovernmental Oceanographic Commision: Expert missions to Indian Ocean countries to assess requirements and capacity for an effective and durable national tsunami warning and mitigation system. Bangkok and Chiang Mai, 18-20 August 2005. Paris, UNESCO 2005. IOC Mission Report No. 27, 29 November 2005.

UNESCO-IOC (2008): TsunamiTeacher – Resource Kit. Intergovernmental Oceanographic Commission, UNESCO (2008), http://www.ioc-tsunami.org/