Tsunami and Coastal Disaster Risk Management in Indonesia

Taming the Impossible?! Tsunami and Coastal Disaster Risk Management in Indonesia

- Training Module -

by Eberhard Krain, Dewi Yanurita and Anne-Katrin Link Purwokerto 8th – 17th August 2006

Joint International Workshop cum Training Course “Coastal Ecosystems: Hazards Management and Rehabilitation”

General Soedirman University (UNSOED), Purwokerto Centre for Science & Technology of the Non-Aligned and Other Development Countries (NAM-Centre), New Delhi, India Center for Tropical Marine Ecology (ZMT), Bremen

List of Contents

1. INTRODUCTION ...... 4

2. CAUSES OF TSUNAMIS ...... 4

3. PHYSICAL PROPERTIES OF TSUNAMI WAVES ...... 7

3.1 What is a Wave? ...... 7

3.2 Tsunami Waves vs. Wind-generated Waves ...... 10

3.3 Energy Transformation ...... 12

3.4 Deep-water vs. Shallow-water Waves ...... 12

3.5 Definition of Shore Face Border ...... 15

3.6 Wave Refraction ...... 16

4. CHARACTERISTICS AND DIMENSIONS OF TSUNAMIS ...... 18

4.1 Tsunami Trough and Crest ...... 18

4.2 How Many Tsunami Waves Are Common? ...... 19

4.3 Size of Tsunamis...... 20

4.4 Where do Tsunamis Occur? ...... 20

5. THE TSUNAMI EARLY WARNING SYSTEMS (TEWS) ...... 22

5.1 Pacific Tsunami Warning Center (PTWC) ...... 22

5.2 Deep-ocean Tsunami Detection ...... 23

5.3 The German-Indian Ocean Tsunami Early Warning System (GITEWS) ...... 24

6. WHAT TO DO IF A TSUNAMI IS APPROACHING (SOURCE: NASA OBSERVATORIUM (1999)) ...... 26

7. NATURAL BUFFERS FOR COASTLINES ...... 26 1 7.1 Coral Reefs ...... 26

7.2 Mangroves ...... 27

7.3 Coastal Terrestrial Vegetation ...... 27

8. DISASTER MANAGEMENT IN INDONESIA ...... 27

8.2 Institutional Framework for Natural Disaster Management in Indonesia ...... 28 8.2.1 Decentralization Laws and Handling of Disasters ...... 28 8.2.2 Disaster Risk Management on National Level ...... 28 8.2.3 Disaster Risk Management on Regional and Local Level ...... 29 8.2.4 Problems in Disaster Risk Management ...... 29

8.3 The Relationship Between Coastal Disaster Risk Management and Integrated Coastal Zone Management ...... 29

8.4 People‘s Attitude...... 31

9. CONCLUSIONS ...... 32

10. GLOSSARY (SOURCE: NOAA/PMEL (2006)) ...... 34

11. SELECTED READINGS AND REFERENCES ...... 38

12. ANNEX: ANSWERS TO QUESTIONS ...... 41

2 List of Figures FIGURE 1A -1C) TSUNAMI GENERATION ...... 5 FIGURE 2A) WAVE PROPERTIES: WAVE PARAMETERS...... 7 FIGURE 3) THE FAMOUS KRAKATAU ERUPTION IN 1883: WAVE HEIGHT IN METERS AND RUN TIME OF THE TSUNAMI IN MINUTES. SOURCE: NIEDEK AND FRATER (2004:22)...... 9 FIGURE 4) MAP VIEW AND WAVE PROFILE OF WIND-GENERATED WAVES. SOURCE: PINET (1998:239) ...... 10 FIGURE 5A) WAVE TRAINS: MERGING OF 2 WAVE TRAINS. SOURCE: SCHWARZER (2006) ...... 11 FIGURE 6) WAVE ENERGY TRANSFORMATION AT THE SHORELINE, SOURCE SCHWARZER (2006)...... 12 FIGURE 7A) THE MOTION OF WATER PARTICLES BENEATH WAVES. WAVE MOTION WITH DEPTH ...... 13 FIGURE 8A) THE DISTORTION OF WATER-PARTICLES ORBITS IN SHALLOW WATER. DEEP- WATER WAVE ...... 14 FIGURE 9) THE SHORE FACE DEFINITION ...... 15 FIGURE 10A) WAVE REFRACTION IN SHALLOW WATER. CHANGE IN WAVE DIRECTION IN SHALLOW WATER. SOURCE: SCHWARZER (2006) ...... 16 FIGURE 11A) WAVE REFRACTION AT THE SHORELINE. WAVE REFRACTION IN BAYS. SOURCE: SCHWARZER (2006) ...... 17 FIGURE 12) MODEL OF WAVE CREST (RED) AND THROUGH (BLUE) OF THE INDIAN OCEAN TSUNAMI. SOURCE: RESEARCH CENTER FOR DISASTER REDUCTION SYSTEMS (2005) ...... 19 FIGURE 13) TSUNAMI THREATENED COASTLINES OF THE WORLD. SOURCE NIEDEK AND FRATER (2004:20)...... 21 FIGURE 14) TSUNAMI HAZARD MAP OF THE WORLD. SOURCE:OAK RIDGE NATIONAL LABORATORY IN NATIONAL GEOGRAPHIC (APRIL 2005) [INDONESIAN VERSION OF THE NATIONAL GEOGRAPHIC]...... 22 FIGURE 15) THE PACIFIC TSUNAMI WARNING CENTER (PTWC). SOURCE NIEDEK AND FRATER (2004:25) ...... 23 FIGURE 16) THE DEEP-OCEAN ASSESSMENT AND REPORTING OF TSUNAMIS (DART) SYSTEM. SOURCE: NOAA (N.P.) ...... 24 FIGURE 17) THE GERMAN INDIAN OCEAN TSUNAMI EARLY WARNING SYSTEM (GITEWS) AS PLANNED BY THE GFZ, SHOWING THE LOCATION OF THE PLANNED BUOY SYSTEMS, TERRESTRIAL AND COASTAL TIDE STATIONS. SOURCE: GEOFORSCHUNGSZENTRUM POTSDAM, WESER KURIER (2006)...... 25 FIGURE 18) ACTIVE AND POTENTIALLY ACTIVE VOLCANOES IN INDONESIA. SOURCE: EFFENDI ET.AL. (2004:7)...... 27 FIGURE 19) CONEPTUAL VIEW OF THE GEOHAZARD SYSTEM. SOURCE: EFFENDI ET.AL. (2004:9) ...... 28 List of Tables TABLE 1: DIFFERENT MANAGEMENT STYLES BY DISASTER PHASES 31

3 1. Introduction

Natural extreme events, such as floods, earthquakes or storms, can cause much damage to people, property, and nature. During the 26th December 2004 Tsunami off the coast of northern Sumatra, Indonesia, many coastal communities along the shores of the Indian Ocean were affected. In Indonesia more than 230,000 people died or remained missing and hundred thousands lost their homes. This reader will explain and summarize the physical characteristics of tsunamis and reflect the current state of tsunami risk management, particularly with respect to Indonesia where the authors gathered some insights, including risk perception of the communities and the legal framework. This reader shall equip students and practitioners in coastal management initiatives with an in-depth understanding of tsunamis and provide them with some hands-on guidance for preparing coastal disaster risk management plans or to incorporate these into broader coastal zone management plans and initiatives.

2. Causes of Tsunamis

Tsunamis are caused by earthquakes, landslides (above or underwater), volcanic eruptions, or nuclear explosions. Even impacts from outer space (meteorites, asteroids, and comets) or portions of icebergs breaking into the water (so-called “fjord tsunamis”) in a fjord, a narrow ocean inlet surrounded by cliffs, can generate tsunamis. But the most frequent cause for tsunami generation is an earthquake. In the following text and diagrams the scenarios of the plate tectonics before, during and after an earthquake in Indonesia, resulting in a tsunami wave, will be described similar to the December 26th, 2004, tsunami in the Indian Ocean off Aceh, Indonesia. At the start of the earthquake, the Indian-Australian plate moved against and underneath the Eurasian plate (figure 1). Then the Indian-Australian plate flexed down, by which it was warped spring-like due to the built up tension, resulting in a rise of the coastal zone (figure 1b). When the tension was too high, the plate “snapped” at the plate boundary. Hereby, the nose of the overriding plate pushed out and moved the water body lying above it virtually triggering the tsunami. After the tension was released, the coastal area was lowered again (figure 1c).

4

figure 1a -1c) Tsunami generation

figure 1b)

figure 1c)

Figure 1a-c Tsunami generation. (1) The Australian plate moves against and underneath the Eurasian plate. (1b) the Indian-Australian plate flexes down, and is warped spring-like, resulting in a rise of the costal zone. (1c) The nose of the overriding plate pushes out and moves the water body lying above it, and the coastal area is lowered again. Source: SOEST (2006).

This was the “birth” of the tsunami: the water body above the plate was lifted up by the snapped plate (figure 1d). After about ten minutes waves radiated and progressed outwards from the center of the earthquake. Firstly; a depression occurred at the earthquake center (figure 1e). After a short while, the propagating movement of the wave uplifted the water body in the center again, and the radiating waves propagated towards the coastline (figure 1f).

5 figure 1d) Tsunami generation

figure 1e)

figure 1f)

Figure 1d-1f: Tsunami generation. (1d) The water body above the plate is lifted up by the snapped plate. (1e) A depression occurs at the earthquake center. (1f) The water body in the center is uplifted again, and the waves propagate towards the coastline. Source: SOEST (2006).

Questions/Tasks:

1) What are the main important causes to generate a tsunami 2) What is the most common cause for a tsunami and what happens?

6 3. Physical Properties of Tsunami Waves

3.1 What is a Wave?

In general we can say that a wave is any periodic, vertical displacement of a surface. Waves are produced by a generating force and a restoring force; it then propagates away from the source of disturbance. Figure 7 shows a vertical profile of an idealized ocean wave.

figure 2a) Wave properties: Wave parameters.

figure 2b) Idealized wave spectra

Figure 2a-2b: Wave properties. (2a) Wave parameters: regular, symmetrical waves are described by their height, wavelength and period (the time one wavelength takes to pass a fixed point). (2b) Idealised wave spectrum: waves are classified according to their wave period.

7 The scales of wave height and wave period are not linear, but logarithmic, being based on the power of 10. Source: Pinet (1998: 229).

Regular, symmetrical waves can be described by their parameters, which are

• Wave height, which is the distance from trough to crest • Wave length, which is the distance from crest to crest or trough to trough and the

• Wave period. The wave period is the time span which is needed for one complete wavelength to pass through a fixed point.

Waves can be classified according to their wave period (figure 8). A tsunami is a series of ocean waves of extremely long wave length and long period generated in a body of water by an impulsive disturbance that displaces the water. Tsunami waves usually have a wave speed of 500 - 600 mph (800 -1000 km per hour), a wave period of 10 minutes to 2 hours apart and a wave length of 60 - 300 miles apart (100 - 500 km apart). The anatomy of a tsunami wave is similar to that of a wind-generated wave, which usually has a wave speed of 5-60 mph (8 -100 km per hour), a wave period of 5-20 seconds apart and a wave length of 300-600 feet apart (100 - 200 meters apart) (http://library.thinkquest.org/04oct/01797/dynamics/birth.html). The velocity of a wave depends on the depth of the ocean. The deeper the ocean is, the faster the wave travels! Figure 9 shows the propagation of a tsunami wave during the famous eruption of the Krakatau in 1883 in the Sunda Strait (the strait between Java and Sumatra).

8 Run time of the Wave height in meters tsunami in minutes figure 3) The famous Krakatau eruption in 1883: wave height in meters and run time of the tsunami in minutes. Source: Niedek and Frater (2004:22).

Questions/Tasks:

3) Look at figure 3. How long did it take the tsunami to reach the various cities (Banten, Jakarta, Balimbing, Katimbang, Kotaagung, Sumur, Anyar)? How high are the waves? Which factors do you think are important to make predictions about when a tsunami will reach a certain coastline and how high the waves will be? 4) Tsunamis reach a speed up to 500 miles per hour. What would account for such high velocities? 5) How fast can tsunamis travel? (Source: Bigelow Laboratory for Ocean Sciences (2006)). Speed of propagation is V = square-root of (g * h) V is the velocity in meters per second g is the acceleration of gravity, 9.8 meters per (second) h is water depth in meters

6) Calculate: 9 a) If the water depth is 3000 meters, what is the velocity of the wave? b) If the water depth is only 50 meters, what is the velocity of the wave? c) If the velocity is 15 meters per second, what is the depth of the water?

3.2 Tsunami Waves vs. Wind-generated Waves

Most of the waves present on the ocean’s surface are wind-generated waves. Size and type of wind-generated waves are controlled by: • wind velocity, • wind duration, • fetch, and • the original state of the sea surface.

As wind velocity increases, wave length, period and height increase (but only with sufficient wind duration and fetch!). Where waves are generated, e.g. within a storm or very windy area, waves with many periods and heights and lengths are present. Due to the wave interference the seas are irregular within the fetch area (figure 10). Outside of the fetch area ocean swells develop as they sort themselves. With distance from the storm the length of the wave crest increases, and swells lose their energy very slowly, and can even travel the entire length of the Pacific, from the Antarctic to Alaska! The significant wave height is the average wave height of the highest 1/3 of the waves present and is a good indicator of potential for wave damage.

figure 4) Map view and wave profile of wind-generated waves. Source: Pinet (1998:239)

10 As a matter of fact, two wave trains (frequency of wave) can merge (shown in red and blue) (figure 11) of slightly different wave lengths (but the same amplitudes), to form wave groups (figure 12).

figure 5a) Wave trains: Merging of 2 wave trains. Source: Schwarzer (2006)

figure 5b) Wave group formation of wave groups.

Tsunami waves are characterized by

• long wave lengths (> 150 km), • small wave heights (0.5-1m), and • high velocities (700-900 km/hour).

They may cross an entire ocean within 24 hours. In contrast to that, wind-generated waves have shorter wave lengths.

Questions/Tasks:

7) What is a wave? 8) How can a wave be described and classified? 9) What are wind generated waves controlled by? 10) What is the difference between wind-generated waves and a tsunami wave in the open sea with respect to wave properties?

11 3.3 Energy Transformation

Waves moves through the open ocean. As the waves encounter water depths smaller than 1/2 wavelength, friction removes energy, wave length decreases and wave height increases. The wave period stays constant (figure 6). The waves decrease in height relative to width and become longer on the top than on the bottom. This results in greater net motion of the water in the direction of the wave. The period of the wave stays the same, but length and speed decrease. The wave becomes steeper/higher (since steepness is height/length) and when steepness is >1/8 it breaks. Breaking releases the wave's energy and leads to a transport of water and sediment. If the water is very shallow compared to the wavelength (D/L<1/20), then the speed of a wave is strongly determined by the water depth.

figure 6) Wave energy transformation at the shoreline, Source Schwarzer (2006).

3.4 Deep-water vs. Shallow-water Waves

Deep-water waves are defined as waves moving through water that is deeper than its own wave base, which is one half its wave length. Intermediate-water waves travels through water depths that are between one half and one twentieth the wave length, whereas shallow water waves occur in water less than one 20th of the wave length. In deep-water waves, wave motion is not detectable at depths deeper than half a wave length. This border is called „wave base“. In figure 7a, the blue arrows symbolise the motion of water particles beneath the waves. As one wave length

12 passes, a water particle at the surface moves through a circular orbit with a diameter equal to the height of the wave. Particles below the surface also move through orbits with the passage of a wave. The orbital diameter decreases with depth (figure 7b). The orbits beneath the waves are slightly open, which results in a net displacement of water (mass transport), which also allows the drifting of water particles (figure 7c). This shows that the wave energy, not the water particles, travel across and through the water!

figure 7a) The motion of water particles beneath waves. Wave motion with depth

figure 7b) Orbits of water figure7c) Stokes drift

Figure 7a-7c) The motion of water particles beneath waves. (7a) Wave motion with depth: the arrows at the sea surface denote the motion of water particles beneath waves. With the passage of one wavelength, a water particle at the sea surface describes a circular orbit with a diameter equal to the wave’s height. Water particles below the sea surface also describe orbits with the passage of each wave, as indicated by the back-and-forth motion of seaweed attached to the ocean floor. (7b) Orbits of water particles: the orbital diameters described by water particles beneath waves decrease rapidly with distance below the surface. Wave-induced water motion essentially ceases at depth (wave base) that is equal to one half of the wavelength. (7c) 13 Stokes drift: the orbits described by water particles beneath waves are not closed, but slightly open. This results in a net displacement of water, called mass transport (Stokes drift), in the direction of the wave advance. Source: Pinet (1998:233).

Questions/Tasks:

11) Discuss why a tsunami in open water is barely perceptible but can reach great heights as it approaches land.

Figure 8a shows that the particle orbits in deep-water waves are in circles and decrease in diameters with depth. In opposite to that, shallow-water wave orbits are compressed vertically into elongated ellipses and progressively flatten their orbits towards the sea-bed (figure 8b). When a wave enters shallow water, it is slowed down by friction. .This causes the orbits, especially in the lower part of the wave, to become elliptical. BUT: the speed of these elliptical movements does not decrease with water depth as in deep water waves.

figure 8a) The distortion of water-particles orbits in shallow water. Deep-water wave

figure8b: Shallow-water wave

14 Figure 8a-8b: The distortion of water-particle orbits in shallow water. (17) Deep-water wave: for deep-water waves, the orbits described by water particles beneath waves are circular. (18) Shallow-water wave: for shallow-water waves, the orbits of water particles are greatly compressed vertically into elongated ellipses. Source: Pinet (1998: 235).

Questions/Tasks:

12) Calculate whether a tsunami wave is a deep-water wave or a shallow water wave. For the calculation use a minimum tsunami wave length of 150 km. 13) Can you think of a reason why it could be important whether a tsunami wave IS a shallow water wave? 14) What happens when a wave approaches the coastline? 15) What are wave trains? How can you apply this to tsunamis?

3.5 Definition of Shore Face Border

Johnson defined the border of the shore face border as the point where the wave base first meets the seafloor, and where the energy transformation starts (figure 9). For tsunami disaster management it is important to consider the local geomorphology, as it affects the behavior of the wave onshore.

figure 9) The shore face definition 15

Figure 9: The shore face as defined (a) explicitly by Johnson (1919). (b) loosely by Niederoda & Swift (1991) and (c) by Cowell et al. (1999) by extending Johnson’s definition in relation to the natural geodynamic continuum. The curve at the bottom schematically depicts the relationship between time scale and scale of morphological change. (from Cowell et al., 1999). Source: Schwarzer (2006).

Questions/Tasks:

16) What implications does Johnson’s definition of the shore face border have for natural hazard management issues? Hint: In case of a tsunami wave, where do you think would the shore face border be?

3.6 Wave Refraction

Wave behavior changes when they approach shallow water. They start to bend when they propagate towards the coastline (figure 10a). Waves travel more slowly in shallow water (shallower than the wave base) than in deeper water. This causes the wave front to bend so it is more parallel to shore (figure 10b).

figure 10a) Wave refraction in shallow water. Change in wave direction in shallow water. Source: Schwarzer (2006)

16 figure 10b) Change in velocity in shallow water.

Refraction causes waves to approach the shoreline at low angles. In bays energy is spread out by refraction (figure 11a). At headlands the wave energy is concentrated by refraction (figure 11b).

figure 11a) Wave refraction at the shoreline. Wave refraction in bays. Source: Schwarzer (2006)

figure 11b: Wave refraction at headlands

17 However, what happens when (like in the case of a tsunami) the wave travels on shore? On gently sloping coasts a giant tsunami can develop, and on sudden steep coasts a tsunami can be blocked towards the coast. In addition to that, the morphology of a coastline affects the height of the approaching wave in such a way, that in bays the waves get higher due to the funnel-like shape of the coast, while on headland the waves are diverted and get smaller.

4. Characteristics and Dimensions of Tsunamis

4.1 Tsunami Trough and Crest

In many reports on tsunamis it is described that a wave trough was visible first. During the 26th December 2004 tsunami the trough arrived at the coast of Sumatra first; but contrary to that, on the Lankan/Indian coastline the crest arrived first. In a simulation (figure 12) it can become visible how the wave crest (red) might have propagated towards India, whereas the wave trough (blue) moved towards the Indonesian coastline. It depends on the plate tectonic how a tsunami is generated and whether a wave crest or wave trough will arrive first at the coast. Off Sumatra usually first a trough arrives and it takes about 20-30 minutes until the wave crest reaches. This gives people about 10 to 20 minutes to run to higher grounds after noticing a wave trough.

18 figure 12) Model of wave crest (red) and through (blue) of the Indian Ocean Tsunami. Source: Research Center for Disaster Reduction Systems (2005)

Questions/Tasks:

17) We know now that it is never certain whether a wave crest or a wave trough would arrive at the coast first. What would this mean for management implications? 18) According to what you just read, what precautious advise could you give to people living very near to the coast?

4.2 How Many Tsunami Waves Are Common?

It is a common belief that the first tsunami wave is the worst and strongest. This belief can be fatal. There can be several waves, and according to records in Hawaii even up to 12! During the 26th December 2004 Tsunami wave no. 4 was the most destructive, and in one of the tsunamis striking Hawaii it was wave no. 8.

19 Questions/Tasks: 19) You were to give advise to people living near to the coast, how to behave after the first wave has passed. What would you advise?

4.3 Size of Tsunamis

The size of a tsunami depends on the size of the trigger (most commonly: earthquakes), the morphology (bathymetry) and the substrate and vegetation (coral reefs/mangroves present?) of the shoreline. On the sea it is very hard to “see” a tsunami wave, unless a tsunami early warning system detects it. Commonly the wave crest is only about 0.5 to 1 m high in the open ocean and does not differ much to the other wind-generated waves around it. Approaching the land, water walls („bore”) can emerge which can be up to 30 – 40 m high. Tsunamis can be very destructive due to water walls/flooding, but also due to the back-flow of the flood pulling back into the sea, which might be loaded with items from the coastline (cars, trees, etc.).

Questions/Tasks: 20) Imagine you have a well-functioning early warning system, you know when the wave will arrive and have a few hours to go until the wave arrives. Which advise could you give to ship owners who have their ships anchored in the harbor?

4.4 Where do Tsunamis Occur?

Potentially threatened coastlines worldwide are displayed in figure 13. According to records, 80% of all tsunamis strike in the Pacific Ocean, and have affected countries along the western coastline of the American continent, South-East Asia and the Pacific island groups. Due to the high frequency of earthquakes, the Indian Ocean is also at high risk. There are regions of the Mediterranean Sea and New Zealand, both with regions of high volcanic activity, who also have a higher tsunami risk. Predictions were made for “Cumbre Vieja”, an active volcano of the Spanish Canary Islands, from which 500 km³ of rock might slide into the sea at any time in the future. This is indeed a potentially very dangerous tsunami generator to the Atlantic Ocean, and waves could even reach distant areas such as the USA!

20 Tsunami threatened coastlines of the figure 13) Tsunami threatened coastlines of the world. Source Niedek and Frater (2004:20).

The “Tsunamis hazard map of the world” shows the potential tsunami risk for different regions in the world (figure14). Indonesia has the greatest potential risk from all regions, in particular Padang, West Sumatra. But vulnerability is also high for the South Java coast.

21 Padang, West Sumatra

Cilacap, South Java

figure 14) Tsunami hazard map of the world. Source:Oak Ridge National Laboratory in National Geographic (April 2005) [Indonesian version of the National Geographic].

5. The Tsunami Early Warning Systems (TEWS)

5.1 Pacific Tsunami Warning Center (PTWC)

The Pacific Tsunami Warning Center (PTWC) is operated by the National Oceanic and Atmospheric Administration (NOAA) in the USA. It is a tsunami warning system which can give international tsunami predictions and issue warnings for the Pacific Ocean region. This center was established after Aleutian Island earthquake and a tsunami, which resulted in 165 losses of human lives in Hawaii and Alaska in 1946. The PTWC uses seismic data to start with, but also accounts oceanographic data, provided by tide gauges in the area of the earthquake (figure 14). These can assure whether a tsunami wave is formed or not.

22 Seismographic stations Run-time of a tsunami in Tide gauges hours figure 15) The Pacific Tsunami Warning Center (PTWC). Source Niedek and Frater (2004:25)

5.2 Deep-ocean Tsunami Detection

In 1995, NOAA started with the development of the “Deep-ocean Assessment and Reporting of Tsunamis” (DART) system. The DART system consists of seafloor bottom pressure recorder (BPR), and a surface buoy. Data from the BPR on the seafloor is transmitted to the surface buoy by an acoustic signal. Then the data is transmitted to ground stations via satellite, where the data then can be analyzed and possible threats detected (figure 16). Up to 2001 only six stations had been deployed. The advantage of this system is that buoys can give information on the tsunami wave while it is still far out in the ocean, providing more time for evacuation and other measures. After the Indian Ocean Tsunami, plans were made to extend the number of DART buoys by 32 until 2007.

23 figure 16) The Deep-ocean Assessment and Reporting of Tsunamis (DART) system. Source: NOAA (n.p.)

5.3 The German-Indian Ocean Tsunami Early Warning System (GITEWS)

The GITEWS (German-Indonesian Tsunami Early Warning System) project, funded by the BMBF (Bundesministerium für Bildung und Forschung), aims to establish an effective Tsunami Early Warning System for Indonesia and the Indian Ocean, and to enhance capacity building in Indonesia. The project is coordinated by the GFZ- Potsdam (Geo-Research Center Potsdam), which facilitates studies on tsunami detection measures, including ground-based or space-borne radar sensors. In addition to that it conducts research by modeling, investigating for example earthquakes as tsunami triggers, wave propagation in deep & shallow waters, and wave propagation on coast. Figure 17 shows the planned setup of the GITEWS.

24 Buoy System Terrestrial station Coastal tide stations figure 17) The German Indian Ocean Tsunami Early Warning System (GITEWS) as planned by the GFZ, showing the location of the planned buoy systems, terrestrial and coastal tide stations. Source: Geoforschungszentrum Potsdam, Weser Kurier (2006).

The project faces tremendous technical and management challenges. Many places along Sumatra or Java only have about 5 – 15 minutes for early warning (while there are about 2-3 hours for India and Sri Lanka and half a day for countries along the East African shores). The safety of the buoys cannot be taken for granted. There might be pirates and ordinary fishermen taking the equipment. The maintenance cost are also high (abut 1 million Euro per year). Indian Ocean nations could not agree (yet) on establishing a central warning agency comparable to the Pacific Tsunami Warning System in Hawaii. However, national warning centers around the Indian Ocean shall be established and coordinated by UNESCO. In 2008 the German- Indonesian Tsunami Early Warning System shall be operational technically.

Questions/Tasks:

21) Look at figure 29. Discuss the locations of the planned stations and buoys.

25 6. What to Do if a Tsunami is Approaching (Source: NASA Observatorium (1999))

“If you are in a dangerous area, immediately turn off the water, gas, and electricity and quickly move to higher ground. Remember, once a Tsunami Warning is issued, it could be a matter of minutes, or even seconds, before the wave hits. If a Tsunami Warning is issued, NEVER go down to the beach to watch the waves come in; you won't live to tell the story. Remember also that a tsunami is a series of waves. Often the first wave may be the least dangerous. The waves may get progressively worse as time goes by. Listen to a portable radio to learn when it is safe to return home. After a tsunami has hit, all food and water should be tested for contamination before it is eaten. All buildings should be checked for gas leaks and electrical shorts before anyone enters. Administer first aid only if you know what to do. Stay tuned to local radio and TV stations, especially NOAA Weather Radio, for evacuation orders if a Tsunami Warning has been issued. Do NOT return to low-lying areas until the tsunami threat has passed and the "all clear" is announced.”

7. Natural buffers for coastlines

7.1 Coral Reefs

Coral reefs are the first buffer in front of the coastline, and are said to provide a significant protection by breaking the force of a tsunami in- and under-water before the waves hit the shoreline. It is assumed that the buffer is functioning more effectively the healthier the reefs are; and pre-damaged reefs appear to provide much less shore protection. For instance, mined corals reefs in Sri Lanka showed that the tsunami found gaps through the reefs and hit the coast much more forceful: where there were no corridors the Tsunami only went up to 50 meters on the coast; in one instance with a corridor (from coral mining) the Tsunami went 1.5 km inland and hit a passenger train killing 1.700 people!

26 7.2 Mangroves

Mangrove forests give the best natural coastal protection due to the special anatomy of their roots (stilt, prop-roots and pneumatophores), which break the waves and can take out a high amount of the tsunami wave’s energy. According to Mazda et al. (1997) a mangrove forest may reduce a tsunami wave by 20 cm every 100 m. Moreover, it may save people’s lives. When the wave recedes it might prevent them from getting swept into the sea.

7.3 Coastal Terrestrial Vegetation

Trees, tree crops, and plantations (oil palms and coconuts) may also provide a significant buffer to some extent. Less effective are annual or seasonal crops, and rather ineffective is bare land or shrimp ponds.

8. Disaster Management in Indonesia

On average, 200-300 disasters occur in Indonesia each and every year, by which 300-400 people lose their lives, thousands of people get homeless, and millions of $ are lost due to losses to the sea, and damage to properties. Indonesia is at high risk of natural disasters as it is located in an area where three tectonic plates border. With 190 volcanoes Indonesia is the country with the highest amount of volcanoes world- wide (figure 18), and earthquakes and natural disasters happen quite frequently.

figure 18) Active and potentially active volcanoes in Indonesia. Source: Effendi et.al. (2004:7)

27

figure 19) Coneptual view of the geohazard system. Source: Effendi et.al. (2004:9)

With assistance of the German-Indonesian GeoRisk project various types of disasters were systematically investigated and analyzed with respect to the causes, the vulnerability and interlinkages.

8.2 Institutional Framework for Natural Disaster Management in Indonesia

8.2.1 Decentralization Laws and Handling of Disasters

With promulgation of the laws on decentralization (No. 22/1999 and 25/2001 on Regional Autonomy), disaster management became the task of local governments. The law intends an increasing public participation at all levels of political decision making. Disasters that cross the border of a district (kabupaten) are then following under the jurisdiction of the province. If a natural disaster happens, several provinces central government will become responsible.

8.2.2 Disaster Risk Management on National Level

The “National Coordination Board for Natural Disaster Management” (BAKORNAS PBP) was created by decentralization law and Presidential Decrease 3 and 11 of 28 2001. It was first a non-structural body and since December 2005 a structural body (having their own staff and budget) to work out, coordinate, guide, monitor, and standardize the national approach for disaster management. It is also responsible for internally displaced persons (IDP) and refugees, and guides and monitors actions directed against man-made hazards. It is placed under the Vice-President of Indonesia; and a secretariat of the board has been established under the Ministry of Social Welfare. The board integrates key ministries like Finance, Health, Home Affairs, Social Welfare, Public Works, the provincial governments and representatives of the military and the police.

8.2.3 Disaster Risk Management on Regional and Local Level

SATKORLAK PBP, the Provincial Unit for Coordination of Disaster Risk Management, is responsible on provincial level and is chaired by the provincial governor. On district or municipal level, SATLAK PBP (District Unit for Implementation of Disaster Risk Management), chaired by the head of the district (“Bupati”), becomes responsible. SATGAS, the Task Force for Disaster Risk Management works on local, sub-district level.

8.2.4 Problems in Disaster Risk Management

A big problem that has become evident is that a conducive and coherent legal framework for natural disaster management in Indonesia is missing so far. Laws and presidential decrees stipulating functions of bodies and ministries are often contradicting and/or overlapping, and there is a heavily fragmented line of responsibilities which makes a coherent handling of emergencies difficult. Most local governments are neither technically, administratively, nor financially capable to comply with the tasks of disaster management, plus there is a general lack of specific disaster mitigation knowledge, skills and information. Up to today, a reactive rather than a preventive disaster approach is taken. Budgets in annual planning documents are usually missing for disaster management.

8.3 The Relationship Between Coastal Disaster Risk Management and Integrated Coastal Zone Management

It is usually said that coastal disaster risk management should be made part of integrated coastal zone management. However, in Indonesia (and possibly in many

29 other countries, too) there is a divide between these two functions and there is also a divide on how the management of disasters and regional development should be approached.

With respect to the organizational divide: Integrated coastal zone management is part of the functions of the national or regional development planning agencies (in Indonesia: BAPPENAS and BAPPEDA), while disaster risk management is executed by the Vice President and the Minister for Social Welfare on national level and Governor/Bupati and an agency directly subordinated to him on provincial or district level, respectively. Thus for an effective disaster risk management these different organizations have to work closely together (and often they don’t).

With respect to the management approach divide: Integrated coastal zone management should usually work in a participatory manner involving all stakeholders. This is usually a lengthy matter. However, once a disaster has struck, fast action and a command-like approach is needed. Thus these two functions (integrated coastal zone management and disaster risk management) appear to need be tackled in fundamentally different ways!

Though these two functions appear difficult to be reconciled, this is not so drastic when one attempts to differentiate between the different phases of good disaster risk management, as can be seen in the following compilation:

30

Phases of a Disaster Management Styles/Mechanisms 1. Before a disaster: disaster Usually enough time available to analyze preparedness problems and to come to agreement between all stakeholders, government and non-government agencies. A participatory management style can be well employed. 2. At a disaster: organizing relief Usually very little time is available to save measures human lives and prevent further damages to infrastructure. A fast and commando-like style is necessary. 3. After a disaster: Rehabilitation and Here usually there is again time to reconstructionr involve stakeholders properly and to coordinate between the various government and non-government agencies. Here a participatory management style can be employed again. Table 1: Different Management Styles by Disaster Phases

8.4 People‘s Attitude

Attempts were made to find out more about the attitude towards natural disasters of people living in areas that are at risk of a tsunami. So far there is only scattered anecdotal evidence.

Makassar, South Sulawesi, Provincial Government While organizationally regional development planning and management appeared strong (BAPPEDA), disaster risk management appeared rather weak. In Makassar, at the South Sulawesi Provincial Government no strategy, vision or plan was in place for disaster risk management, while this was the case for regional development planning.

31 Makassar, Barrang Lompo Island (near Makassar, South Sulawesi) Little need to prepare for disasters could be noticed at Barrang Lompo Island: the general attitude of people is that „disasters cannot be predicted and prevented“and/or that „it is God‘s punishment“. General problems on livelihood are in the fore ground, such as having enough income and food, to be healthy and to be educated.

Maumere, Flores In Maumere, Flores the overall attitude seems to be that disasters are up to God and good faith can give protection. Many people still do not know much about natural disasters because of their relatively low level of education. Even if people know of natural disasters, many continue life like before (near the coast), because of their tradition and customs. To some fishermen adjustments would mean more transport cost if they had to move to higher grounds. Moreover, some do not want to leave because there are also their places of worship and burial.

Padang, Sumatra At Padang high awareness and interest of the society and local government in natural disasters is evident. People in this area are psychologically traumatized by catastrophes, with more than 200 earthquakes in 2005. Development of risk maps, evacuation routes, and evacuation routines to some extent are already prepared to some extent.

9. Conclusions

Indonesia is one of the most disaster prone areas in the world. The current disaster risk technology and management is far from being able to respond adequately to disasters, and disaster risk management had played a rather small role in the minds of many people and government/s on national as well as regional and local levels. This, however, has changed since the 26th December 2004 Tsunami. A Tsunami Early Warning System shall now be established with international assistance. An early warning system will, however, remain a big problem on the west coast of Sumatra or the south coast of Java since there is a very short warning time (less than 15 minutes) (in contrast to Hawaii, where it usually takes several hours until the island is hit by a tsunami). Apart from tremendous technical challenges, a lot of work is also needed to link to and organize coastal people. It is recommended that

32 preparation for disasters at the coast should be part of future management plans. However, management structures in Indonesia follow partly very different organizational lines (disaster risk management is in a different body than regional development planning), which complicates implementation. In conclusion: a lot of work still remains to be done!

33 10. Glossary (Source: NOAA/PMEL (2006))

Amplitude: The rise above or drop below the ambient water level as read on a tide gage. Arrival time: Time of arrival, usually of the first wave, of the first wave of the tsunami at a particular location. Bore: Traveling wave with an abrupt vertical front or wall of water. Under certain conditions, the leading edge of a tsunami wave may form a bore as it approaches and runs onshore. A bore may also be formed when a tsunami wave enters a river channel, and may travel upstream penetrating to a greater distance inland than the general inundation. CREST: Consolidated Reporting of Earthquakes and Tsunamis, a project funded through the Tsunami Hazard Mitigation Federal/State Working Group to upgrade regional seismic networks in AK, WA, OR, CA, and HI and provide real-time seismic information from these networks and the USNSN to the tsunami warning centers. ETA: Estimated Time of Arrival. Computed arrival time of the first tsunami wave at coastal communities after a specific earthquake has occurred. First motion: Initial motion of the first wave, a rise in the water level is denoted by R, a fall by F. Free field offshore profile: A profile of the wave measured far enough offshore so that it is unaffected by interference from harbor and shoreline effects. Harbor resonance: The continued reflection and interference of waves from the edge of a harbor or narrow bay which can cause amplification of the wave heights, and extend the duration of wave activity from a tsunami. Horizontal inundation distance: The distance that a tsunami wave penetrates onto the shore, measured horizontally from the mean sea level position of the water's edge. Usually measured as the maximum distance for a particular segment of the coast. ICG/ITSU: The International Coordination Group for the Tsunami Warning System in the Pacific, a United Nations organization under UNESCO responsible for international tsunami cooperation. IDNDR: International Decade for Natural Disaster Reduction, a United Nations sponsored program for the 1990's.

34 Inundation: The depth, relative to a stated reference level, to which a particular location is covered by water. Inundation area: An area that is flooded with water. Inundation line (limit): The inland limit of wetting measured horizontally from the edge of the coast defined by mean sea level. ITIC: International Tsunami Information Center established in 1965. Monitors international activities of the Pacific Tsunami Warning Center and assists with many of the activities of ICG/ITSU. Leading-depression wave: Initial tsunami wave is a trough, causing a draw down of water level. Leading-positive wave: Initial tsunami wave is a crest, causing a rise in water level. Also called a leading-elevation wave. Local/regional tsunami: Source of the tsunami within 1000 km of the area of interest. Local or near-field tsunami has a very short travel time (30 minutes or less); mid-field or regional tsunami waves have travel times on the order of 30 minutes to 2 hours. Note: „Local" tsunami is sometimes used to refer to a tsunami of landslide origin. Maremoto: Spanish term for tsunami. Marigram: Tide gage recording showing wave height as a function of time. Marigraph: The instrument which records wave height. Mean Lower Low Water (MLLW): The average low tide water elevation often used as a reference to measure run-up. Ms: Surface Wave Magnitude. Magnitude of an earthquake as measured from the amplitude of seismic surface waves. Often referred to by the media as "Richter" magnitude. Mw: Moment Magnitude. Magnitude based on the size and characteristics of the fault rupture, and determined from long-period seismic waves. It is a better measure of earthquake size than surface wave magnitude, especially for very large earthquakes. Calibrated to agree on average with surface wave magnitudes for earthquakes less than magnitude 7.5. NOAA: National Oceanic and Atmospheric Administration, the federal agency responsible for tsunami warnings and monitoring. Part of the Department of Commerce.

35 NWS: National Weather Service, the branch of NOAA which operates the tsunami warning centers and disseminates warnings. Normal earthquake: An earthquake caused by slip along a sloping fault where the rock above the fault moves downwards relative to the rock below. Pacific Disaster Center (PDC): An information processing center to support emergency managers in the Pacific region. Funded by the U.S. Department of Defense. PTWC: Pacific Tsunami Warning Center. Originally established in 1948 as the SSWWS, located in Ewa Beach near Honolulu. Responsible for issuing warnings to Hawaii, to U.S. interests in the Pacific other than the west coast and Alaska, and to countries located throughout the Pacific. Period: The length of time between two successive peaks or troughs. May vary due to complex interference of waves. Tsunami periods generally range from 5 to 60 minutes. Run-up: Maximum height of the water onshore observed above a reference sea level. Usually measured at the horizontal inundation limit. Seiche: A standing wave oscillating in a partially or fully enclosed body of water. May be initiated by long period seismic waves, wind and water waves, or a tsunami. Strike-slip earthquake: An earthquake caused by horizontal slip along a fault. SSWWS: Seismic Sea Wave Warning System, the original tsunami warning center established in 1948 after the April 1, 1946 tsunami killed 159 people in Hawaii. Teletsunami: Source of the tsunami more than 1000 km away from area of interest. Also called a distant-source or far-field tsunami. THRUST: The project for Tsunami Hazard Reduction Using System Technology, sponsored by the Office for U.S. Foreign Disaster Assistance/Agency for International Development. A comprehensive program to mitigate tsunami hazards in developing countries. Thrust earthquake: An earthquake caused by slip along a gently sloping fault where the rock above the fault is pushed upwards relative to the rock below. The most common type of earthquake source of damaging tsunamis. Tidal wave: Common term for tsunami used in older literature, historical descriptions and popular accounts. Tides, caused by the gravitational attractions of the sun and moon, may increase or decrease the impact of a tsunami, but have nothing to do with their generation or propagation. However, most tsunamis (initially) give the

36 appearance of a fast-rising tide or fast-ebbing as they approach shore and only rarely as a near-vertical wall of water. TIME: The Center for the Tsunami Inundation Mapping Effort, to assist the Pacific states in developing tsunami inundation maps. Travel time: Time (usually measured in hours and tenths of hours) that it takes a tsunami to travel from the source to a particular location. Tsunami: A Japanese term derived from the characters "tsu" meaning harbour and "nami" meaning wave. Now generally accepted by the international scientific community to describe a series of travelling waves in water produced by the displacement of the sea floor associated with submarine earthquakes, volcanic eruptions, or landslides. Tsunami earthquake: A tsunamigenic earthquake which produces a much larger tsunami than expected for its magnitude. Tsunamigenic earthquake: Any earthquake which produces a measureable tsunami. Tsunami magnitude: A number which characterizes the strength of a tsunami based on the tsunami wave amplitudes. Several different tsunami magnitude determination methods have been proposed. TWS: Tsunami Warning System, organization of 26 Pacific Member States which coordinates international monitoring and warning dissemination. Operates through ICG/ITSU USNSN: United States National Seismic Network, operated by the USGS. Monitors, in real-time, magnitude (M)>5 earthquake activity worldwide and M>3 in conterminous US.UTC Universal Coordinated Time, international common time system, formerly GMT (Greenwich Mean Time). UTC: Universal Coordinated Time, international common time system (formerly GMT, Greenwich Mean Time). WC/ATWC: West Coast/ Alaska Tsunami Warning Center, established in 1967 originally to issue warnings to Alaska of local tsunami events. WC/ATWC is now responsible for issuing warnings for any event likely to impact either Alaska, the west coast of the US, or the Pacific coast of Canada. WCM: Warning Coordination Meteorologist, regional weather service person responsible for providing information on the tsunami warning system to local agencies.

37 11. Selected Readings and References

Bernard, P. (2005) Tsunamis im Mittelmeer? Spektrum der Wissenschaft, 4/2005.

Bigelow Laboratory for Ocean Sciences (2006) Tsunami experiment- crosscurricular ideas. http://www.bigelow.org/virtual/handson/tsunami.html#glossary

Dudley, Walter C.; Min Lee. (1998) Tsunami! 2nd ed. University of Hawaii Press.

Effendi, A.; Nasution, A.; Djarwoto, A.; Murdohardono, D.; Kertapati, E.; Hermawan; Hidajat, R.; Sutawidjaja, I.S.; Jäger, St.; Manhart, A.; Ranke, U.; Rehmann, T.; Dalimin, R.; Sugalang; Weiland, L. (2004) Mitigation of Geohazards in Indonesia, Status Report on the Project “Civil-society and Inter-municipal Cooperation for Better Urban Services / Mitigation of Geohazards. GeoRisk Project, Bandung.

Hwang, D.J. (2005) Hawaii Coastal Hazard Mitigation Handbook. School of Ocean and Earth Science and Technology, University of Hawaii, Hawaii.

Tomascik, T-; Mah, A.J.; Nontji, A.; Kasim Moosa, M. (1997) Tsunamis. In Coral Reefs: Natural Disturbances, The Ecology of the Indonesian Seas, Vol. VII, Part I, Oxford University Press, Chapter 11.

ISORI-ICSARD, BPPT (2005) Tsunami Effect on Coastal Zone of Nanggroe Aceh Darussalam and North Sumatra Provinces (Draft).

Krumme, Uwe. (2005) Die südasiatische Tsunami-Katastrophe – Ökologische Aspekte des Desasters und der Folgenbewältigung [The Southeastasian Tsunami Catastrophe – Ecological Aspects of a Disaster and Coping with Its Impact], Presentation on 8th June 2005 at the Bundesamt für Seeschifffahrt, Hamburg,. Center for Tropical Marine Ecology (ZMT), Bremen.

Mazda, Yoshihiro, Magi, Michimasa, Kogo, Motohiko and Phan Nguyen Hong (1997) Mangroves as a coastal protection from waves in the Tong King delta, Vietnam, Mangroves and Salt Marhes 1: 127-136.

38

NASA Observatorium (1999) What to do when they hit. Accessed on 1.3.2006. http://observe.arc.nasa.gov/nasa/exhibits/tsunami/tsun_hit2.html

Niedek, I.; Frater, H. (Eds) (2004) Naturkatastrophen, Springer Verlag, Berlin.

NOAA: DART 2 System. Accessed on 20.4.2006. http://nctr.pmel.noaa.gov /Dart/Jpg/DART_II_metric-page.jpg, n.p.

NOAA/PMEL: Tsunami terminology. Accessed on 15.3.2006. http://www.pmel.noaa.gov/tsunami-hazard/terms.html

Oak Ridge National Laboratory (2005) Tsunami Hazard Map of the World. National Geographic: 4/2005.

Patlis, J.M. The Role of Law and Legal Institutions in Determining the Sustainability of Integrated Coastal Management Projects in Indonesia

Patlis, J.M.; Knight, M.; Benoit, J. (2003) Integrated Coastal Management in Decentralizing Developing Countries: The General Paradigm, the U.S. Model, and the Indonesian Example. Ocean Yearbook 17: 380-416.

Pinet, P. (1998) Invitation to Oceanography. Web Enhanced edition. Jones & Bartlett.

Research Center for Disaster Reduction Systems: December 26, 2004 Earthquake Tsunami Disaster of Indian Ocean. Accessed on 21. March 2006. http://www. drs.dpri.kyoto-u.ac.jp/sumatradrs, 2005

Roberts, E. (2005) Prepare for the Worst: It’s Going to Happen, Marine Scientist No. 10 (1): 20-23.

Schwarzer, K. (2006) ISATEC Lecture 1: Introduction.

39 SOEST: How is a Tsunami Generated? 1. By an Earthquake. Accessed on 21. March 2006. http://www.soest.hawaii.edu/tsunami/tsugen.html, 2006

Weserkurier. Nr. 59, 2006

Wood, E. (2005) Tsunami und Korallenriffe, Koralle 6(2), Heft 32, April/May, 72-76.

40 12. Annex: Answers to Questions

1) Earthquakes, landslides (above or underwater), volcanic eruptions, nuclear explosions, impacts from outer space or portions of icebergs breaking into the water can generate tsunamis.

2) The most frequent cause for tsunami generation is an earthquake. In the case of the 26th December 2004 Tsunami off the coast of northern Sumatra, Indonesia, the Indian-Australian plate moved against and underneath the Eurasian tectonic plate. Over time, the Indian-Australian plate flexed down, by which it was warped spring-like due to the built up tension, resulting in a rise of the coastal zone. When the tension was too high, the plate “snapped” at the plate boundary, and an earthquake occurred. Hereby, the nose of the overriding plate pushed out and moved the water body lying above it. After the tension was released, the coastal area was lowered again. The water body above the plate was lifted up by the snapped plate. Waves radiated and progressed outwards from the center of the earthquake. Firstly; a depression occurred at the earthquake center. After a short while, the propagating movement of the wave uplifted the water body in the center again, and the radiating waves propagated towards the coastline.

3) Banten: 90 min, 1.8m Jakarta: >110 min, 1.8m Balimbing: 60 min, 15m Katimbang: 40 min, 24m Telukbettung: >60 min, 36m Kotaagung: >60min Sumur: 60 min Anyar: 40 min, 41m Characteristics and depth of the seabed, morphology of coastline (bay or headland), land or island that gets in the way of the wave.

41 4) Impulsive disturbance that displaces the whole water body locally. The velocity of a wave depends also on the depth of the ocean.

5) If the wave depth is 3000 meters, what is the velocity? 171, 46 m/s (617 km/h) If the water depth is only 50 meters, what is the velocity? 22.14 m/s (80 km/h) If the velocity is 15 meters per second (54 km/h), what is the depth of the water? 22.96m

7) In general we can say that a wave is any periodic, vertical displacement of a surface. Waves are produced by a generating force and a restoring force; it then propagates away from the source of disturbance. [Trainer to demonstrate a wave generation with a rope or a spring balance].

8) Waves can be described by: Wave height, wave length and wave period. Waves can be classified according to their wave period.

9) Wind velocity, wind duration, fetch, and the original state of the sea surface.

10) Wind-generated waves are slower, have a shorter period, have much shorter wave lengths but are usually higher in wave height. Most striking is the difference in wave length and this will drastically reflect in a difference of wave base depth.

Wave type Speed Period Wave length Wave height Tsunami 800 – 1000 10 min – 2 h 100 – 500 km 100 – 500 km waves km/h Wind waves 8 – 10 km/h 5 – 20 sec 0.1 – 0.2 km 0.01 – 15 m

11) In the open sea tsunami wave are hardly perceivable: the wave height is not more than 0.5 – 1 m and it takes 10 minutes to 2 hours from one wave crest to the next! When approaching the coast, however, there is a huge energy transformation because of the tremendous depth of the wave base causing early and strong friction between wave and sea/coast bottom.

42 12) We know that the wave length of a tsunami is defined to be more than 150 km. For this case, we calculate how deep the sea would need to be so that a tsunami wave is a deep-water wave. As previously mentioned, for a deep-water wave the water depth needs to be larger than half of the wave length. This would mean that the wave base would be 150 km /2= 75 km! As a matter of fact, the average ocean depth is 3000- 4000 meters, and even the maximum depth of the deepest trench in our oceans does not exceed 11 km. Therefore tsunamis are in no way deep-water waves!

For assessing if a tsunami wave is a shallow water wave we divide 150 km by 20 = 7.5 km. This is still much larger than the average ocean depth of 3000 – 4000 meters (admittedly there are some trenches in the ocean that are deeper than 7.5 km). For most cases we can conclude that even in the open ocean the tsunami wave is a shallow water wave.

13) Modeling approaches of tsunamis for early warning systems, the characteristics of the seafloor need to be integrated into the model.

14) Waves move through the open ocean. As the waves encounter water depths smaller than 1/2 wavelength, friction removes energy, wave length decreases and wave height increases. The wave period stays constant. The waves decrease in height relative to width and become longer on the top than on the bottom. This results in greater net motion of the water in the direction of the wave. The period of the wave stays the same, but length and speed decrease. The wave becomes steeper/higher (since steepness is height/length) and when steepness is >1/8 it breaks. Breaking releases the wave's energy and leads to a transport of water and sediment. If the water is very shallow compared to the wavelength (D/L<1/20), then the speed of a wave is determined by the water depth.

15) Wave frequencies that can team up and become wave groups. This could explain why the first wave does not necessarily need to be the most destructive wave.

43 16) The shore face border is defined to be where the wave base meets the seafloor. In case of the tsunami wave, which is a shallow water wave, a tsunami meets its shore face border right after having been generated, already in the open ocean. Thus for a tsunami the coast literally starts right in the middle of the ocean. This fact is important for the propagation of the tsunami wave and more importantly for the forecasting of the propagation in propagation models. Thus typically propagation models for tsunamis have to start already far from the coast.

17) Management should consider both possible scenarios, and should inform their communities. They should be able to recognizing the threat and act correspondingly.

18) Watch the sea and how it changes. Pay special attention to the sea after an earthquake. If you see the tide going out more than usually, quickly look for a high spot where you will be save from the wave.

19) Don’t return to your house, as the first wave is not necessarily the most destructive wave. Wait for at least 2 hours and until the threat is over. Wait for an official announcement that it is safe to return.

20) Leave the harbor and near coast, move out into the sea. Wait there until the threat is over.

21) Buoys mainly located at the coastlines, therefore detection is only possible when the wave already approaches the coast; not much time will be left to alarm the local communities and to act. Countries that are further away benefit rather than countries closer to the tsunami generation zone.

44