Tsunamis and Tsunami Warning Systems

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HYDRAULIC STRUCTURES, EQUIPMENT AND WATER DATA ACQUISITION SYSTEMS – Tsunamis and Tsunami Warning Systems - William Mansfield Adams, Sr. , Jan Malan Jordaan, Jr.

TSUNAMIS AND TSUNAMI WARNING SYSTEMS William Mansfield Adams, Sr. Hawaii Institute of Geophysics, University of Hawaii, and 3682 Prevost Way, Ferndale WA 98248-9004 USA. Jan Malan Jordaan, Jr. Pr. Eng., (retired). , Arcadia 0007, Pretoria, South Africa Keywords: Tsunami, seismic sea wave, earthquake, seismic disturbance, wave generation, wave runup, wave refraction, wave dispersion, energy dissipation, warning systems, shoreline, ocean energy, continental shelf, tidal wave, bathymetry Contents 1. Overview 2. The Tsunami Phenomenon 3. Generation Mechanics 4. Parameters of the Source of a Tsunami 5. Theory and Measurements 6. Division of Tsunami Energy at a Typical Continental Shelf Edge 7. Tsunami Runup onto Land 8. Solving the Tsunami Problem for Actual Geometries: Numerical Modeling 9. The Third Dimension: The Shape of the Coastline 10. Warning Systems for Tsunamis 11. Concluding Remarks Appendix Glossary Bibliography Biographical Sketches To cite this chapter Summary This article describes the source mechanism, generation, and transmission of seismic sea waves (tsunami) across the global ocean surface. The dispersion, refraction, and transformation by the continental shelf of these potentially disastrous “tidal” waves are described, as well as alarm systems to provide early warning for evasive action and evacuation strategies to be implemented in a timely manner. Prototype and model data are also discussed and theoretical relationships presented. The article covers in detail the origins of tsunami from deep-seated seismic disturbances on the ocean floor, seen in historic perspective. The theory of tsunami generation, propagation across the global oceans, and terminal effects on shorelines around the world is presented. This includes source energy parameters, generation mechanics, energy redistribution at the continental shelves, and runup phenomena over coastal slopes. Because of the long periodicity and a wavelength several times the depth of the ocean traversed, a tsunami is effectively a shallow-water wave, and its progression and terminal effects can be described by shallow-water wave theory.

©Encyclopedia of Life Support Systems (EOLSS)

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The impact and threat of tsunami on coastal and inland populated areas have been severe in isolated cases in the past; nevertheless, the threat to circum-Pacific and other coastal localities is recognized, and tsunami warning system networks have been set up. Seismic observations, early warnings of tsunami generations, and estimated travel and arrival times are issued by the authorities involved. Numerical modeling analysis is carried out and confirmed by observations made during actual occurrences. 1. Overview The course of human civilization was changed abruptly by a tsunami, or seismic sea wave when, in 1450 BC, the volcano Santorini in the Aegean Sea erupted explosively and, in conjunction with caldera collapse and related faulting, sent out a series of waves that devastated the northern coast of Crete. The Minoan society, then the highest culture in the Western world, never recovered. Other disastrous tsunamis have occurred in Calabria and Sicily, and elsewhere in Europe, also in the Pacific Ocean: Chili, Alaska, Japan, Philippines, Indonesia (Krakatoa 1883) mostly in conjunction with earthquakes, but also as a result of volcanic explosions. The word tsunami is derived from Japanese, denoting port or harbor (tsu) and sea wave (nami) caused by seismic activity, which phenomenon along with earthquakes are well known to the people of Japan and Asia. This natural hazard is dreaded and respected whenever a major earthquake in the circum-Pacific volcanic belt is reported. With the earthquake source providing its energy, a tsunami propagates thousands of kilometers over the ocean to coastlines and shores, where it impacts with varying degrees of severity (see Nature of Earthquakes). Much more frequent than in Europe are the tsunamis in the Pacific Ocean, usually due to undersea tectonic dislocations, such as in geological faults along the deep ocean trenches. These tsunamis may have vertical motions at their source of more than 10 m (much more in a few rare cases). Because wave amplification may occur, the resulting tsunamis may have runup on adjacent coastlines of 20 m to 30 m amplitude—and as much as 10 m to 20 m runup on distant shorelines (see Plate Tectonics). As an introduction to the tsunami phenomenon and to tsunami-warning systems, first consider idealized cases of the generation of a tsunami, its propagation, and its runup onto a sloping beach. These cases are all so simple that theoretical analysis is possible, even though the runup problem is strongly disproportional. Concentration on elementary situations involves a few parameters and permits understanding of the relationships between the parameters. After grasping the fundamentals, more realistic conditions for models of the ocean-earth conditions are considered. These are treated by numerical methods—finite-difference or finite-element. All of the foregoing is done for a cross-section of the ocean, from the undersea generating source to the runup on the beach. This is a two-dimensional process, although sometimes called one-dimensional because an integration process eliminates the second dimension, the vertical dependence in deep water (more than 200 m). When the third dimension—that is laterally along the shoreline—becomes important, the possible extent of the effects of the additional dimension may also be evaluated (see Hydraulic Structures for Coastal Protection).


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Tsunami warning systems are much more complicated even than tsunamis themselves, because people and instruments are also involved. Six tsunami warning systems exist worldwide: French, Russian, Japanese, Hawaiian, Aleutian, and Pacific. These are also discussed below. 2. The Tsunami Phenomenon Like ancient Gaul, the tsunami phenomenon can be said to be divided into three parts. The beginning is the generation of the tsunami; the middle is the tsunami propagation across one or more oceans; and the end is the termination and runup of the tsunami onto a coastline. Certain features of the tsunami need to be known. These are called parameters, from which a predictive capability has to be developed. Some parameters can be measured directly, but others must be deduced from measurement of some of the different characteristics; so the interrelationships among these parameters are of continual concern in our study. 3. Generation Mechanics The typical tsunami is formed by an earthquake—a tectonic earthquake, which means that the crust of the earth, deep down, is deformed permanently or temporarily during the earthquake. The vertical component of the deformation, up or down, will lift or lower any overlying part of the ocean. If there is no ocean, there will be no tsunami. The earthquake represents the relatively sudden conversion of potential energy, in the form of crustal rocks strained on each side of a fault, into kinetic energy, which works, first, by moving the rock, including the emission of seismic waves; second, by lifting the overlying ocean; and third, by heating the fault interface, which is not of present interest. Lifting of the ocean occurs slowly, on the order of tens or hundreds of seconds, so the water does not fly off into space but simply temporarily forms a raised mound of water atop the vertically deformed crust. This mound of water has potential energy, because it is at a higher potential in the gravity field of the Earth than it was before being uplifted. And being in an unstable condition, this potential energy is immediately converted into kinetic energy. The water elevated in the mound, however, does not flow off the mound, as might be expected, but bears down on the water underneath, which then has to move sideways because it cannot pass into the underlying rock. Energy thereupon spreads out in the form of a water-wave system, as the mounded water area begins to oscillate up and down. Consider the generation situation schematically shown in Figure 1. The total potential energy of the mound of water is the density, times the area, times the mean rise (where ρ is the density, S is the area, and η is the mean rise, equal to one half the rise, ηtotal). The density may be approximated as unity, and the less significant kinetic energy that the earthquake directly puts into the water may for simplification be ignored.


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Figure 1. Cross-section of an ocean showing the generation process of a tsunami: the uplifted portion of the ocean floor raises the overlying ocean to form a mound of water

having potential energy 4. Parameters of the Source of a Tsunami Assume the source area is circular in plan and that the uplift is uniform over the source area. The area of uplift in a large earthquake—such as would generate a tsunami hazardous to humankind—has radial dimensions of hundreds of kilometers, as indicated by the distribution of aftershocks and other water evidence. This radial length determines the dominant wavelength of the radiated gravity-type water waves or tsunamis, and, most important, is more than an order of magnitude greater than the average depth of the ocean, which we take to be about 4 km. Water wave theory indicates that this is a special extreme case, called the shallow-water or long-wave approximation. This simplification is permissible, even though the ocean is not thought of as being “shallow.” The propagation velocity, V, for such long wavelengths, long compared to the depth, is independent of wavelength and depends only on the value of gravitational acceleration, g, and the depth of water, H: thus V = √


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(gH). The relationship of tsunamis to other types of waves such as ocean swell and tides is described in detail elsewhere. The uplift occurs in about one minute over the entire source region: there are some other interesting features dependent upon this rate of uplift and the properties of the fracturing material, but these are not relevant here. For larger earthquakes, greater than about Richter magnitude 7, the source area will be elongated along the strike of the fault, which usually lies parallel to the adjacent coastline. This, too, leads to important variations in the radiation pattern, which are not further discussed here. To keep the model simple, the uplift is assumed to occur due to a source area situated in the deep ocean; the effect of a tsunami being created in a coastal area is considered later. Because the driving cause of a tsunami is the potential energy due to uplift in a gravitational field, the tsunami is called a “gravity wave.” As the energy of the tsunami spreads out from the source, there are two different velocities involved, and understanding the difference is important. The rate propagation, at which the front of the wave spreads outward, is known as the wave velocity, or celerity, of the tsunami. For a water depth of 4 km and a gravitational acceleration field of 9.8 m/s2, this celerity is about 200 m/s—equal to about 720 km/h. This is the velocity of the energy propagation, not the velocity of the water itself. The particles of water move and interact in such a manner as to transfer the energy radially outward along the travel path of the tsunami. Both theory and observations indicate that this particle velocity is much lower, being only about 2 cm/s (72 m/h). This is the reason the passage of tsunamis in the deep ocean is not noticed by observers on ships at sea. The orbit of the particle of water during the passage of a tsunami is shown in Figure 2.

Figure 2. Cross section showing the particle motion at the ocean surface: the particle velocity has both vertical and horizontal components with the horizontal component

being dominant—about 10 times the vertical component The shape of a simulated tsunami, moving outward from an impulsive source across an ocean of constant depth, was determined theoretically, and is shown in Figures 3(a) and 3(b).


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Figure 3. (a) and (b) Cross section of the surface of the ocean with a propagating tsunami (and no tide or swell);

The vertical axis denotes the amplitude and the horizontal axis the distance. This is the theoretical prediction of what a tsunami would look like if the entire ocean were suddenly frozen and a vertical slice taken out along the path of the tsunami. We cannot do this, but we can look at Mare Orientalis on the Moon, which is partly visible through binoculars or telescope (Cherrington) and seen edge-on from the Earth on the last quarter limb of the waning Moon. This impressive feature is seen (on images from space) to be surrounded by concentric circular ridges and troughs, as is shown on the enclosed image taken from a Moon-orbiting spacecraft, Figure 3(c). This might be evidence of a “frozen” tsunami.


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Figure 3. (c) Mare Orientalis on the Moon, as seen from space, in a NASA image, possibly a “frozen tsunami”

In Figure 3 (a) and (b), each oscillation has the appearance of a sinusoid. The horizontal axis is distance. The beginning of the tsunami is abrupt and the decay is gradual. The distance between the peaks is the wavelength, and the height of the peaks above the mean is the amplitude. For upward motion of the ocean floor at the source, the first wave formed will also be upward from the mean sea level, and for a downward sea floor motion at the source the first wave will also be downward. Some sources have both downward and upward areas of sea floor motion, e.g., vertical faulting in deep water leading to an infinite variety of possible complications. The energy lost propagating across the deep ocean is negligible; passage over an archipelago, such as the Hawaiian Islands, however, causes significant transformation of the tsunami wave form, reduction of the amplitude, and possibly frequency modifications. 5. Theory and Measurements To check out the theory, it is necessary to know, first, the distance between the peaks (or troughs), and second, the amplitude of the peaks (or troughs). The problem is to derive such answers from what can be measured. Measurements of tsunamis in the ocean use the common tide recorder, which is located at a fixed distance from the source and records how the amplitude at that particular, single, radial distance varies with time as the tsunami passes the gauge; in other words, a time-record is obtained. A copy of such a recording of a tsunami is shown in Figure 4.


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Figure 4. Typical recording, at one spot, of the passage of a tsunami. The horizontal axis here is time; the time between consecutive peaks is the period; the height of the

peak above the mean is the amplitude. From this recording, one can determine, first, the periodicity of the oscillations, usually of the order of about 1000 s, and, second, the amplitude of the oscillations, usually up to about 1 m in the deep ocean. If measurements are obtained at two different radial distances from the source (and in nearly equal water depths) for the same tsunami, then one can determine the wave propagation velocity or celerity, V. (Already knowing the period, T, with the wave celerity, V, thus known, one can determine the wavelength, L, from the relationship: L = V × T.) This is how one derives what one wants to know from what one can measure. The loss of energy during propagation or attenuation is negligible compared with the energy loss upon reflection of the tsunami from a coastline; and the dispersion or radial spreading (due to the dependence of the velocity of propagation upon the wavelength, or period) is also negligible in the deep ocean, at least within the first few wavelengths away from the source region. There is one other complicating feature that needs to be understood. Propagation of a tsunami over the Earth's surface means the tsunami energy is spreading over the spherical Earth and not over an infinite flat plane. To simplify understanding, consider a planet uniformly covered with water: the amplitude (and energy density per unit area of surface) of a propagating tsunami will reduce as it spreads out to an angular displacement of 90° about its center (until it reaches an “equator” relative to its source). Because the same energy up to this point is being spread out over a greater perimeter, as shown in Figure 5, one can say that the energy is diverging and therefore being diluted.


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Figure 5. Propagation of a tsunami across a global ocean, such as the Pacific Ocean Then comes the complication: beyond 90° angular displacement from the source, because the tsunami is spreading out farther over a sphere, convergence of the energy resumes, and the amplitude gradually becomes larger again with increasing radial distance! Ignoring this (and tsunami history) was disastrous for Japan in May 1960 during the Chilean tsunami, which originated almost at Japan’s antipode on the spherical earth ocean. 6. Division of Tsunami Energy at a Typical Continental Shelf Edge A tsunami propagates across the deep ocean as a shallow-water gravity wave, with a wave celerity of about 700 km/h, much greater than the maximum particle velocity of about 70 m/h. In a few hours, the tsunami arrives at the edge of a continental shelf or an island, but first consider only the continental shelf edge. The typical cross-section is as shown in Figure 6 (note the vertical exaggeration). About 50% of the tsunami energy is reflected from the edge back into the ocean. However, as the tsunami enters the shoaling water, the wavelength shortens and the amplitude increases; the period remains constant (except at barrier reefs where amplitudes may decrease and wave frequencies may double)


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Figure 6. Cross section of a typical continental shelf edge. The continental shelf is about 1° in slope with the horizontal and the continental edge about 7° in slope. The width of the continental edge is about 25 km; this is much smaller than the wavelength (200 km) of the dominant wave period (1000 s) of the tsunami, so the continental edge can effectively be approximated as a step. For reasonable depths of the continental edge and the deep ocean, theoretical studies indicate that about 50% of the energy of the tsunami is reflected back into the ocean; the remaining 50% crosses the continental edge onto the continental shelf. On the continental shelf itself, the period of the dominant wave energy of the tsunami remains the same—about 1000 s, but because the wave propagation velocity is far lower than in the deep ocean, the wavelength now shortens to about 30 km, and the amplitude increases by a factor of about 10, from energy conservation principles. One assumes the simple case of the tsunami approaching (i.e. incident) at right angles to the continental edge; incidence at a lesser angle adds complication. Advancing over the continental shelf, the depth is continually shoaling—becoming shallower as the tsunami approaches the coast. The change of wave amplitude with shoaling water depth and due to wave refraction is given by Green’s Law, Eq. (1), which states:

1 14 2

C D D

D C C

A H BA H B

⎛ ⎞ ⎛ ⎞= ⋅⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

(1)

where A is the amplitude of the tsunami wave (measured from mean still-water level to a peak or trough); H is the depth of the water; B the refracted wave ray spacing, and subscripts C and D refer to coastal and deep water, respectively. (This can also be used in the opposite sense when the source is in a coastal area—for extrapolating the source amplitude outward into deep water. In that case, the amplitude becomes smaller. Approximation of the tsunami as a shallow-water wave is permissible only as long as the water depth is at least 10 times the amplitude of the tsunami. For shallower depths, one must restore the disproportionate terms to the theoretical equation and begin to consider the runup of the tsunami onto the land. In Table 1 the parameters of an idealized tsunami are compared for three locations. ©Encyclopedia of Life Support Systems (EOLSS)

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Deep Ocean

(depth 4 kilometers)

Continental

Edge (depth 200

meters)

Coast

(depth 10 meters)

Wave Period (Seconds)

1000

1000

1000

Wave Frequency (cps)

0.001

0.001

0.001

Wave Velocity (km/hr)

700

100

40

Particle Velocity orbital m/s (Vertical)

0.002

0.02

0.05

Particle orbital Velocity m/s (horizontal)

0.02

0.2

0.5

Wave Length (Kilometers)

200

30

12

Wave Amplitude and vertical particle motion (meters)

1

10

25

Horizontal particle Translation (meters)

10

100

250

Table 1. Comparative parameters of an idealized tsunami for three locations in the

ocean 7. Tsunami Runup onto Land The simplest termination case is the extreme situation of a vertical cliff, extending from the bottom of the ocean up past the water surface (similar to the east coast of Taiwan). Theory predicts that the tsunami amplitude at the cliff face (due to reflection upon itself) will be exactly twice the amplitude of the incident tsunami; the so-called standing wave case. This is confirmed by observations in laboratory experiments, and it should be acceptable intuitively, if the wave at the cliff is recognized as being the arithmetical addition of the reflected wave onto the incoming wave. The next case, a sloping beach, has been solved analytically for only two cases: the uniformly sloping beach and the inverted paraboloidal ocean island. The uniformly sloping beach is as depicted in Figure 7. Some general features can be observed for a typical vertical slope of 10°: the tsunami can be considered as a “fast tide,” i.e. one that takes only 15 min for rising or falling, instead of the customary 6.25 h (or 12.5 h in total tidal rise-fall-rise period). There are complications in the runup process, such as caused by an offshore reef. The case of a shallow barrier reef has been analyzed and is easily observed at many surfing sites. Each incoming oscillation changes into two (or more) waves—the wave transformation is also strongly nonlinear (i.e. disproportionate). Therefore such a barrier significantly reduces the maximum amplitude of the incident wave on the shore (and might double the frequency).


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Another case is known as tidal bores—if the slope of the bottom steepens, then the amplitude of the tidal wave continues to increase and the wavelength to decrease. Continuous breaking of the tidal wave or rolling, as in surf, begins to occur when the wavelength reduces to less than about seven times the amplitude as the wave steepens. For even steeper waves, it becomes what is known as a “tidal bore,” or a continuously rolling, breaking wave. The leading edge of the tsunami, in effect, behaves like this and becomes an advancing wall of water with a frontal slope of about 45 °. This is a far more dangerous condition than the unbroken “fast tide,” which occurs for flatter slopes of the shore. Fortunately, the occurrence of a tsunami-bore is relatively rare, so it will not be considered further here. The run-down phase following the run-up phase can be equally disastrous, or even more so. Several run-up and run-down phases can follow in succession, thus producing progressive devastation. Thus far, idealized conditions have been considered—simplified enough for analytical treatment to be possible. However, one would like to model complex situations that more closely resemble the earth-ocean system, and some indications thereof will be given next. 8. Solving the Tsunami Problem for Actual Geometries: Numerical Modeling The Earth’s surface is much more complicated than the simplified idealizations that have been considered; the purpose of that approach was pedagogical—to focus on the fundamental physics and to understand the primary effects. To include secondary effects, numerical modeling is resorted to, using finite differences or finite elements. These techniques are well known, hence only those aspects especially pertinent to the modeling of tsunamis are mentioned below. Because both tsunami generation and propagation are linear (i.e. proportionate) phenomena in the deep ocean, the application of numerical techniques to include the irregularities of the bathometry seems straightforward, but there is another problem. One cannot simply put in the bathometry (undersea topography) along the apparent direct ray-path, because if there is a seamount, for example, the tsunami will, in effect, go around it—along the fastest route (the energy going over it arriving later). Since tracing out enough propagation rays to detail tsunami behavior at a seamount is therefore not reasonable, the alternative approach that works well is to remove the high spatial frequency content of the bathometry by low-pass filtering. Perhaps one reason such filtering of the bathometry works well is that the bathometry is not accurately known everywhere in the ocean, in particular probably not everywhere where the tsunami energy happens to propagate between source and landfall. The usual technique for developing a chart of the ocean bathometry is to measure the depth at many points in the area of interest. Unfortunately, these points are usually concentrated along convenient paths and are not randomly distributed; hence may be strongly biased and not representative. Since the time for a tsunami to travel from source to landfall depends upon the propagation velocity, which in turn depends on the water depth (square root thereof), an average depth can be obtained by observing the travel time of a tsunami between known points. Indeed, this was the manner in which the first good estimate of the average depth of the ocean was actually obtained. Measurements of the travel time of a tsunami,


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done in 1856, showed the average ocean depth to be about 4 km, instead of the 18 km that had erroneously been assumed previously. The most important follow-up action is to verify the numerical model. This can be done by solving the same problem both analytically and numerically. For this reason, the two analytical solutions that exist for the runup problem were previously emphasized. Computer programs for tsunami modeling, which have not successfully solved such problems, i.e. obtained agreement with the analytical solutions, should therefore not be used. Perhaps the trickiest part in numerical modeling is determining the grid or mesh over which to do the computations. This is obviously dependent on the complexity of the bathometry and how well it is known. A less obvious problem is that the density of the grid is also dependent upon the highest frequency component of the tsunami wave form that one wishes to model. Many, perhaps most, modelers choose two points per wavelength, and blithely believe they are adhering to Shannon’s advice about avoiding aliasing. Unfortunately, Shannon said “at least” two points. In experiments, five points seem to be the minimum acceptable, with 20 definitely being preferred. Much numerical modeling, not just for tsunamis, is unacceptable, therefore, for reasons of not adhering to this strict requirement. Running the model for a tsunami reflecting back and forth in a parabolic basin for (say) 100 laps illustrates the anomalous results that would result with an inadequate modeling technique. 9. The Third Dimension: The Shape of the Coastline Seamounts and inlets: Offshore topography can “focus” energy. If each path or “ray” of the tsunami energy is considered analogous to a ray of light, then one will intuitively know what would happen for a tsunami passing over a seamount, as the path in the middle is traversed slower than the paths off-center (i.e. acting as a convex lens would do in optical theory). As shown in Figure 7 at (a), focusing occurs and the amplification can therefore be greater than twice. Likewise, the amplification along the irregular coastline is not at all uniform. Funneling in a valley: After the tsunami has run up onto dry land and moves like a tidal bore into a valley, the amplitude of the wave (or tsunami bore) will further increase as the valley narrows, because of energy concentration, as shown in Figure 7 at (b). This is a dominant amplification factor for ria coastlines, which are tectonically sinking valleys and slowly drowning the mouths of the rivers; the Sanriku coastline on the northeast part of the island of Honshu, Japan, is the archetype area for ria effects on tsunamis.


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Figure 7. Schematic map of (a) offshore mound and (b) onshore valley. The mound acts like a lens—to focus the tsunami energy—and the valley geometrically funnels the energy, further increasing the amplitudes of the tsunami waves. The runup observed

along a coastline varies by a factor of almost 10. Other special effects: As in most hydrodynamics problems, there are other special situations, such as Mach-stem reflections, and other wave phenomena. However, these are not further considered in this introductory exposition. Graphic account of tsunami and post-tsunami destruction: Tudor gives the following firsthand account of the effects of the Alaskan Good Friday Earthquake of March 27, 1964 based on eyewitness evidence and post-event personal observation at the sites (on Kodiak Island, Alaska, near the epicenter; and at Crescent City, California, the nearest landfall across the Pacific Ocean, some 2500 km away) of the aftereffects of a large earthquake and its accompanying tsunami: • At Kodiak, the series of six seismic sea waves (tsunami) had crests ranging from 4.5

m to 7.2 m above mean lower low water (MLLW) and periods from 27 min to 90 min.

• At Crescent City, the largest wave reached 6.3 m above MLLW and had a period of 55 min.

• A survey of water-wave damage to waterfront facilities at Kodiak, Alaska, and Crescent City, California, made about one week after the March 27, 1964, Alaskan earthquake of about 8.3 Richter scale magnitude, indicated light to moderate damage from 1.2-m to 3-m inundations and heavy damage from impact by wave-driven ships and debris. Piers with moored ships had decking damage; piers with adequate deck to piling connections did not have decking uplifted.


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In a study on hurricane wave forces on a pier at Ventnor City, New Jersey, on the other hand, Tudor found that damage was mainly caused not by the waves directly, but by impacts from floating objects and debris. Tudor recommended that defense or protection should be considered for all low-lying sections of coastal cities and ports in known tsunami-prone environments (see Protection Against Deterioration of Materials and Structures in the Ocean Environment). Runup. Tests at NCEL, Port Hueneme, California, by Jones, Jordaan and Wang showed that wave amplitudes and water motions due to dispersive water waves (such as those generated by rapid displacements and impacts and by underwater or overwater nuclear blasts) are modified because of dispersive effects, thus deviating slightly from the customary Green’s Law predictions (Eq. 1.) for shallow water wave shoaling and refraction cases. The shoreward proceeding wave amplitude for dispersive waves radiating from a point source is inversely proportional to:

• the square root of the orthogonal spacing, • the fourth root of the water depth, and • the square root of the radial travel distance.

The last term accounts for the dispersion effects of the impulsively generated water waves: the waves decay in the radial direction of travel (so-called modified Green’s Law), as compared with the absence of that term for the case of a nondispersive continuous wave train (Green’s Law). Figure 8 (b) illustrates the above concepts as observed in model tests done in a wave basin. These observations for radiating dispersive (shallow-water) waves may to some extent be applicable to tsunami, radiating from a local source and dispersing radially over a global ocean.


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Figure 8. Laboratory experimental data on shore runup of impulsively generated dispersive water waves

10. Warning Systems for Tsunamis A study of warning systems for natural hazards makes one realize that politicians are like some farmers—they lock the barn door after the horse has been stolen. That is warning systems are created soon after a catastrophic event, not before. For example,


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formation of the Pacific Tsunami Warning Center was prompted by the extremely unusual 1946 Aleutian earthquake-tsunami events. The purpose of a warning system should be twofold: first, the long-term objective of zoning hazardous coastal areas to prevent intensive investment or occupation in their most dangerous zones; and second, the short-term objective of warning, in real-time, the occupants of hazardous inundation zones when and where to evacuate. Tsunami-warning systems are of two types: some operate in or adjacent to areas that are sources of tsunamis, so decisions must be rapid, based only on early seismic data (such as the Japanese, Russian, and Aleutians systems in Alaska); others, such as the Hawaiian, Pacific or French systems, are so far removed from most source areas that decision-makers can reasonably anticipate receiving some observations of the water waves in addition to the seismic data. Unfortunately, a significant amount of the information received can be either wrong or ambiguous, leading to uncertainties, possible erroneous warnings, and lack of confidence. There is great variety among the six above-named existing tsunami-warning systems. Tsunami-warning systems are indeed much more complicated than the tsunamis themselves—because people are involved: politicians, public officials, the media, and citizens. Computer simulation of tsunami-warning systems has been informative. The high level of technology available for sensing, processing, transmitting, analyzing, and communicating should ideally therefore make such a warning-system straightforward. 11. Concluding Remarks The phenomena of tsunamis, their origin, generation, travel, and terminal effects have been described. As these life-threatening oceanic processes are being better understood, so precautionary methods and warning systems are being developed. There still remains a great deal of uncertainty as to whether any major tsunami would result from a large earthquake near the coast. The possible arrival time at distant locations can readily be predicted, whereas the degree of danger it might present would not be predictable with certainty. In efforts to provide timely warnings, quite often the very effects warned against might not happen at all. This, coupled with the unpredictability of major earthquakes, has led the public to distrust and even be callous toward tsunami-warning systems. Nevertheless, these phenomena do occur, creating intensive widespread damage, and inhabitants of exposed coastal regions can never be totally immune to tsunami attack. For this reason, time and money devoted to developing and maintaining global tsunami-warning systems are to be considered well spent. However, many factors still make the operation of such systems difficult, such as the following: • Politicians do not want to approve expenditures when benefits are indefinite. • Purchase of instruments is easier than purchase of intangibles, such as education

or training.


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• After a disastrous tsunami, governments may allocate more funding than can be expended wisely in a short time.

• Most people do not think about a hazard until it occurs, and then it is often too late (either to learn at that moment, or to refresh one’s memory about that hazard) to act appropriately towards mitigating the effects.

• Natural scientists know how things work; social scientists know how people operate. Unfortunately, constructive interaction of these two types of scientists seems rare—as rare as tsunamis!

Operating a warning system, especially for events as rare as tsunamis, remains therefore an extraordinarily difficult task. Appendix Appendix 1. Coastal Protection Structures J.M. Jordaan, Pretoria, South Africa 1. Introductory Overview Since the theme of Hydraulic Structures, Equipment and Water Data Acquisition Systems addresses the area of water mainly in the sense of fresh water supply, and not water in the oceans, which cover more than 70% of the earth's surface area, nor fresh water locked up in glaciers and Antarctic ice, which accounts for 90% of the earth's fresh water, it leaves one with a predicament. Should coastal protection structures be included in this theme, or not? Should not snow-melt, ice and glaciers also be dealt with? Hydraulic Structures certainly should include harbors, docks and coastal defense works, breakwaters, piers, jetties, seawalls and groynes. Not even to mention sea outfalls, undersea tunnels, ship canals and locks, which most definitely are hydraulic structures in their own right. That description also applies to floating and anchored offshore oil rigs and undersea pipelines. Many of these examples are life-support systems and do feature prominently in global economics, involving trade routes and fossil-fuel exploitation. Cooling plants for nuclear reactors, and desalination establishments, with their sea-water intakes and brine disposal systems, are definitely hydraulic structures, too. Fresh water lakes, created beside the ocean, by damming arms of the sea at river mouths, exist, as do communication cables crossing ocean floors. Likewise, Water Data Acquisition systems could include ocean-related activities of a meteorological nature (hurricane-watch, storm-surge prediction, tsunami-warning) and coastal-process monitoring (beach erosion and renourishment, intra-coastal waterways, tidal barriers, inland navigation). In this Theme only a few of these aspects are lightly touched on, as very comprehensive treatments of these subjects exist in handbooks, conference proceedings, journals and trade literature. Harbor and dock engineering, the dredging profession, tunnelling, coastal-protection structures, and offshore-oil recovery, are vast well-documented


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disciplines, each represented by several professional societies and their proceedings, and many textbooks. Therefore, this Appendix will merely aim to present some highlights of the endeavours of humankind to enhance and protect coastal living areas, which are of great social and economic importance, and consider some hydraulic works and data collection programs involved. The main article, to which this Appendix is annexed, deals more fully with the tsunami- or seismic-sea-wave problem, and its monitoring and warning systems. To complement that, this article briefly deals with: storm waves and ocean swell, and protection works; tides and tidal barriers; storm surge and coastal protection; weather-watch data collection and prediction. 2. Storm Waves and Ocean Swell Short-period storm waves and long-period ocean swell are generated by sustained wind action anywhere over the global ocean surface. Predictions of waves and swell are made on a regular basis, from satellite observations and generated weather maps, world-wide. The progress of waves and swell across the oceans depends on bathymetry, as they approach coastlines and refract, diffract, reflect, interact and attenuate, due to underwater topography; and also on a number of local shoreline factors such as beaches and estuaries. Wind, weather and wave data are collected for coastlines by local authorities and national agencies such as the US Weather Bureau and the Coastal Engineering Research Center in the USA. The history of protecting and improving coastlines against wave attack, beach erosion and effluent pollution goes a long way back—centuries even, millennia, considering port cities such as Alexandria, Cadiz, Hong Kong, New York, Rotterdam, and Yokohama, to name a few. Harbors protected by breakwaters against storm waves and ocean swell, groynes protecting beaches from erosion, docks, loading terminals and offshore moorings, have to be well-designed to withstand wave action (see Hydraulic Structures for Coastal Protection). The publications of the CERC, mentioned above, deal with the obtaining of data, the theory of wave motion and the design and engineering of protective structures, from breakwaters to sea-walls; and detailed construction techniques, such as sheet-piling, interlocking revetment blocks and dredging. Examples of such works are readily seen world-wide, notably on the Dutch shorelines in the North Sea and the Yssel Meer reconstructions; the eastern shores of the USA, and the California coastline. 3. Tides and Tidal Barriers In the context of protecting coastlines against high tides, both ordinary tides and storm-surges will be considered here. Tides will be dealt with first, then tidal protection, and finally storm surges. 3.1. Tides Tidal action (excluding meteorological storm tides) is caused by the gravitational influence of the sun and moon on the earth's hydrosphere, that body of water surrounding the globe, and known collectively as the world-ocean. Tides are variable ©Encyclopedia of Life Support Systems (EOLSS)

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from location to location along the continental coastlines; but regular in time and predictable by means of tide tables, issued world-wide, giving the dates and times of high- and low-water, and the tidal range, for practically every coastal location on earth. Daily tide ranges differ according to location, from diurnal to semi-diurnal, and monthly tides vary from springs to neaps. Equinoctial spring tide ranges are larger at those times of the year, and solsticial tide ranges smaller. There are many other minor, but regular, variations associated with the astronomical constants of the sun-moon-earth gravitational-dynamic system. Tides can be considered as very long-period gravity waves circling the earth, following the sun and moon's apparent passage around the earth. However, due to the irregular shape of the continental coastlines, rotations and reflections of the tide-wave systems around amphidromic points, are produced, giving rise to very complex, but repetitive, behaviour patterns. These are well charted and tabulated in tidal ephemerides for the harbors of the world. Maintenance dredging goes on continuously, to maintain draft at harbor inlets, principally for low-tide conditions (see Dredging in Rivers and Estuaries). At locations where the tidal range is very high, up to ten or more meters, such as in the Bay of Fundy, Canada, and the Rance estuary, France, hydropower generation has been developed or at least considered. At other locations, such as some of the coastlines around the Mediterranean Sea, the tidal ranges are so low (less than 0.5 meter) as to be almost inconsequential. Elsewhere, the normal mean tide range lies around 1 meter and up to 2 meters, and in a few locations around the world can be as high as seven to ten or even more meters (Gulf of St. Malo, Rance Estuary, Bay of Fundy, etc). 3.2. Tidal Barriers Where tidal barriers are built, they are mainly designed to accommodate and exclude abnormally high tides due to meteorological influence, better known as Storm Tides. In 1953 a prolonged storm system in the north-eastern Atlantic, English Channel and North Sea caused abnormally high tides along the Dutch Coast, coupled with storm waves. Dikes that formed sea-defense works around low-lying areas or polders (which lie beneath mean sea level) were breached in numerous locations, causing widespread flooding damage and a loss of life of 1835 persons, mainly over the province of Zeeland, comprising several interconnected islands. The Dutch Delta-Plan was conceived and built, to put an end to storm-tide threats to these areas. A number of the large river outlet channels forming the Dutch Delta area, the rivers Rhine, Meuse and Eastern Scheldt estuaries around these islands, were closed off by elaborate gated-closure dams. Parts of these inland waters, thus created, became essentially stagnant saline or fresh-water lakes, with some gates normally kept open for passage of ship traffic and others only opened or closed when necessary to exclude high storm tides. One of these estuaries, the Western Scheldt, was for environmental reasons not closed off, but smaller protection works around its inner perimeter were substituted, instead of building a complete tidal barrier there. ©Encyclopedia of Life Support Systems (EOLSS)

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In the Thames estuary, England, a tidal barrier against high storm tides was also built, consisting of a number of rotating horizontal axis sector gates, to allow ships to pass to London docks; but when rotated to the closed position these large gates will exclude storm tides from flooding central London. The Barking tide barrier, near there, is another structure built for the same purpose, and consists of an elevated beam-type gate, rising between towers to the open position, and which can be lowered to close off the tributary against ingress of high storm tides. For Venice, Italy, a system of tide gates is also being considered, so as to avoid very frequent abnormal tidal ingressions. These are a few examples of the most important tidal barriers in existence. The Zuyder Zee's Afsluitdijk (Barrier dam), 30 kilometers in length, completed in 1932, is an example of an arm of the sea having been closed off, for the purpose of freshening it and reclaiming land from the sea (for living and agricultural purposes). Similar closing-off works exist in Hong Kong, where once there was ocean, for creating fresh-water collection reservoirs. 4. Storm Surge and Coastal Defense Storm surges are caused by meteorological conditions, such as typhoons, hurricanes and tropical cyclones. The water level rise is due to low pressure, winds and shoaling effects near coastlines. Superimposed on normal high tides, storm surges give rise to what is commonly called abnormally high tides. 4.1. Storm Surges In hurricane- and cyclone-prone coastal areas, notably the US East and Gulf Coasts, the Philippine Islands, Japan and South-East Asia, a major threat to some very populous coastal habitations is the sea-level rise due to such storm systems. Rises of several meters occur in the low pressure eyes of hurricanes, which when coupled with storm waves and high winds, result in great damage to property, threat to life and inconvenience. 4.2. Coastal Defense Works In areas such as Florida and Louisiana, and Narragansett Bay, Rhode Island (all USA), coastal protection works mitigate to some extent against minor damage. Yet they cannot cope exclusively with major hurricane-onslaughts, which occur nearly on an annual basis, but in different places each time. Nevertheless, the art of beach protection by groynes, sea-walls, and beach renourishment schemes, has been perfected to a high degree, and is well documented, for example in the US Army Corps of Engineers' records of protection works. All over Europe, especially in the Low Countries, such beach protecting works are in evidence. The US Coast Guard, and Weather Bureau, among many world-wide entities of the same kind, maintain observation stations, collect data, and do satellite surveying of weather systems. They issue bulletins and storm warnings to ships at sea and for harbors around the world. Data is published, and daily and weekly weather predictions are made, to issue alerts against potential storm damage, and to report on the progress of ©Encyclopedia of Life Support Systems (EOLSS)

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storm systems. The above considerations are important in the discussion of Tsunamis and Tsunami Warning Systems, as the existing structures built for other purposes of sea protection works may have a bearing on also creating some protection, but not necessarily always, against tsunami hazards. Glossary Aliasing: The possibility of fitting more than one curve (erroneously)

through sampling points lying too far apart. Bathometry: The underwater topography (depth contours or values on a chart,

also known as a hydrographic chart), also spelled bathymetry. Celerity: The speed of advance (propagation velocity) of a particular

wave-form or -shape (not the water particle velocity). Dispersion: Spatial and temporal dilution of energy strength of waves

traveling across the global oceans. Energy: The kinetic and potential ability to do work of a displaced water

mass or of the source of disturbance, interrelated in a complex way.

Group velocity: The speed of advance of a parcel or train of waves (slower than the celerity of the individual waves).

Refraction: Bending of wave rays due to shoaling and slowing down. Richter (scale): Conventional rating of energy of an earthquake at its epicenter

(logarithmic scale). Ria: A Portuguese term denoting a drowned valley-type river mouth

or bay-inlet. Seismic: Pertaining to tremors and motions (earthquakes) originating in

the earth’s crust or below the crust. Sinusoid: A surface of revolution (three-dimensional) of the trigonometric

sine-function. Tsunami: A seismic sea wave. Tsunami warning: A system that is based on advanced indication (earthquake

epicenter location and magnitude) that a tsunami might be expected. Also based on past event data records.

Wave characteristic:

The space-time plot of the advance of a wave feature (crest or trough).

Wave ray: The path of travel of a wave crest in a direction normal to its alignment.

Bibliography

Adams W.M. and Jordaan J.M. (1968). Model Study of Tsunami Amplification around the Island of Oahu, Hawaii. 58pp. Honolulu HI, U.S.A.: Center for Engineering Research, University of Hawaii. [Analysis of experimental studies made, on a vertically-distorted model in the large laboratory wave basin, of a typical tsunami’s terminal amplification around the island’s perimeter, for various incident directions associated with four historic events; which led to positive reproducibility of the observed phenomena in the real case.]

Adams W.M., ed. (1969). Tsunamis in the Pacific Ocean, 513 pp. Proceedings of the International Symposium on Tsunamis and Tsunami Research. Honolulu, Hawaii, US: East-West Center Press.


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[Compendium of papers dealing with tsunami phenomena; (see also the A.W Nekrasov., and the J.A. Williams with J.M. Jordaan entries below).]

Adams W.M. (1972). Simulation of a Tsunami Warning System with a Digital Computer, 187–195. Contributions of the Geophysical Institute No. 12. Kyoto, Japan: Kyoto University. [Practical “hands-on” guide to the application of theory behind a tsunami warning system.]

Ball F.K. (1964). An Exact Theory of Simple Finite Shallow-Water Oscillations on a Rotating Earth. Proceedings of the First Australian Conference of Hydraulics and Fluid Mechanics. New York: Pergamon Press; also in R.R. Silvester, ed. Hydraulics and Fluid Mechanics pp. 293-305, New York: MacMillan. [Basic theory, very useful to tsunami researchers.]

Binder D. (1998). The Duty to Disclose Geological Hazards in Real Estate Transactions, 56 pp. Anaheim, CA, US: Chapman Law Review. [Also relates to possible latent threats of tsunami-generating earthquakes to shore areas prone thereto.]

Braddock. R.D. (1959). Tsunami Propagation over Large Distances 285-302 in: Adams W.M., ed. Tsunamis in the Pacific Ocean, 513 pp. Proceedings of the International Symposium on Tsunamis and Tsunami Research. Honolulu, Hawaii, US: East-West Center Press. [Explains the grid-refinement technique of studying the propagation of tsunamis across great ocean depths and distances; also gives ray-tracks of some major tsunamis.]

Butler J.P. (1967). Double-Humped Waves on a Sloping Beach, Report No. HIG-67-16. Honolulu, Hawaii: University of Hawaii. [Explains how long-period waves are transformed by offshore reefs into multiple waves.]

Carrier G.E. and Greenspan H.P. (1958). Water waves of finite amplitude on a sloping beach. Journal of Fluid Mechanics 4, 97–109. [Basic theoretical treatment of the subject of wave shoaling and runup.]

Cherrington E.H., Jr. (1969). Exploring the Moon Through Binoculars, 181 pp. New York: McGraw-Hill. [Examines a lunar feature (Mare Orientalis) that shows resemblance to a “frozen” tsunami on earth.]

Federal Emergency Management Agency (1997). Guidance on Estimating Substantial Damage: Using the National Flood Insurance Program Residential Substantial Damage Estimator. Washington, DC, US: FEMA. [Practical guidelines, also useful for tsunami damage estimation purposes.]

Glasstone S. (1964). The Effects of Nuclear Weapons, 730 pp. Washington, D.C., US: US Atomic Energy Commission. [Relates the wave-making properties of above-water and underwater disturbances to the energy distribution field at the source. The results of such disturbances are also similar to tsunami-generating effects.]

Hammack J.L. and Segur H. (1978) Modelling Critera for Long Water Waves. Journal of Fluid Mechanics 84 Part II pp 359-373. [Careful review of standard numerical modeling techniques at the time, useful for avoiding such modeling pitfalls as aliasing; and applying the Courant criterion for ensuring stability.]

Hyde M.O. (1969). The Earth in Action, 128 pp. London and Glasgow: Collins. (p49-51 and p87-88). [Description of the 1964 Alaskan earthquake and tsunami; and the major tsunami effects associated with the volcanic explosion and earthquake that devastated, and partly removed, the island Krakatoa in Indonesia in 1883; as well as the historic seismic event at Thera (Santorini) near Crete about 3500 years ago, revealing what might have been the lost city of Atlantis.]

Jones D.B. (1968). Wave Basin Study of Run-up on Beaches from Simulated Underwater Explosions Near Shore, 55 pp. US Civil Engineering Laboratory (Port Hueneme, California) Technical Report R604. Washington, DC, US: Superintendent of Documents. [Continuation of the experimental (physical scale-modeling in a wave basin) and theoretical work on impulsive water waves started by Jordaan, Tudor, and Wang; q.v. entries below.]

Jordaan J.M. (1964). Run-up by Impulsively Generated Water Waves, 73 pp. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Report R330. Washington, DC, US: Superintendent of Documents. [Experimental (using physical scale-models) and theoretical studies of dispersing wave systems, that are similar in certain respects to tsunami.]

Jordaan J.M. (1965). Feasibility of Modeling Run-up Effects of Dispersive Water Waves, 25 pp. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Note N691. Washington, DC,


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US: Superintendent of Documents. [Experimental studies, by means of physical scale-models in a wave basin, of the shoreline runup of wave systems similar to tsunami.]

Jordaan J.M. (1966). Laboratory Simulation of Waves Generated by Underwater Nuclear Explosions, 37 pp. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Report R424. Washington, DC, US: Superintendent of Documents. [Experimentally generated dispersing waves (in a laboratory wave basin) that are similar in certain respects to tsunami, compared well with the properties of dispersing wave systems as predicted by theory.]

Jordaan J.M. (1972). Impulsive Waves: Model and Prototype Correlations. Advances in Hydroscience Vol. 8, 261-304. New York and London: Academic Press. [Describes the generation of impulsive water waves by sudden release of energy, such as from surface water or underwater disturbances, of seismic or explosive origin. Wave propagation and terminal effects were also studied by means of a hydraulic simulation model.]

Kawata Y. (1999). Tsunami in Papua New Guinea was as Intense as First Thought. EOS. American Geophysical Union. [A case history.]

Kranzer H.C. and Keller J.B. (1959). Water waves produced by explosions. Journal of Applied Physics 30 (3), 398–407. [Classical theoretical treatment of explosion-generated water waves, also applicable in certain respects to tsunami.]

Michener J.A. (1969). Hawaii, p. 1012 in Corgi Book Edition. London: Transworld Publishers Ltd. [Graphic description of a tsunami’s devastation wrought on the shores of Oahu, Hawaii.]

Murty T.S. (1977). Seismic Sea Waves: Tsunamis. Ottawa, Canada: Fisheries and Marine Service. [Basic descriptive treatise.]

Nakano M. (1978) Path of Propagation of Tsunami Waves, Marine Geodesy 1 No. 4, pp.331-346. [Explanatory treatment of the wave ray method of tracing the progress of tsunamis across the global oceans.]

Nekrasov A.V. (1970). Transformation of Tsunamis on the Continental Shelf. Tsunamis in the Pacific Ocean (Proceedings of a conference), ed. W.M. Adams, 337–350. Honolulu, Hawaii: East-West Center Press. [The process of amplitude increase of a tsunami approaching a continent.]

Thacker W.C. (1981). Some Exact Solutions to the Nonlinear Shallow-water Wave Equations. Journal of Fluid Mechanics 107, 499–508. [A mathematical and theoretical treatise.]

Tudor W.J. (1964). Tsunami Damage at Kodiak, Alaska, and Crescent City, California, from the Alaskan Earthquake of March 27, 1964, 131 pp. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Note N644. Washington, DC, US: Superintendent of Documents. [Thorough engineering study of after-earthquake tsunami damage to naval waterfront and civilian harbor structures.]

Tudor W.J. (1965). Tsunami Damage. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Note N622. Washington, DC, US: Superintendent of Documents. [A useful review for the practicing ocean engineer.]

Tudor W.J. (1965). Uplift Under A Pier Deck. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Note N668. Washington, DC, US: Superintendent of Documents, [Deals with forces generated by severe waves impacting under a level surface raised above the still water line.]

Tudor W.J. (1965). Ventnor Pier Forces. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Note N578. Washington, DC, US: Superintendent of Documents. [Deals with hurricane wave forces and the resulting damage on a shore facility; it may have an analogy with tsunami wave forces in some aspects of damage assessment.],

Van Dorn W.G. (1968). Tsunamis on the Moon. Nature 220, 1102–1107. [Speculative view that a peculiar concentric lunar feature (Mare Orientalis, observable on the trailing edge of the moon and also from space images) could resemble a “frozen” tsunami on earth.]

Wang H. (1966). Water Waves from Underwater Explosions in Shallow Water, Part I. A Mathematical Model for Waves in Constant Depth and in Shoaling Water, 38 pp. US Naval Civil Engineering Laboratory (Port Hueneme, California) Technical Note N824. Washington, DC, US: Superintendent of Documents. [Describes theoretical numerical modeling of the impulsively generated water-wave systems that were previously investigated experimentally in a laboratory wave basin.]


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Weber D.M., Jones S.J. and Martin D. (1992). Advances in Gas Cloud Dispersion Modeling: Heavy Clouds on Sloping Ground. Major Hazards Onshore and Offshore, p. 351. Institute of Chemical Engineers. [An interesting analogy between water waves and atmospheric shock waves is demonstrated.]

Williams J. A. and Jordaan J.M. Jr. (1969) A Laboratory Model of a Double-Humped Wave Impingent on a Plane, Sloping Beach. 367-376, in: Adams W.M., ed. (1969). Tsunamis in the Pacific Ocean, 513 pp. Proceedings of the International Symposium on Tsunamis and Tsunami Research. Honolulu, Hawaii, US: East-West Center Press. [Experimental and theoretical study of double-humped water waves and their shoaling, as observed for surf and applicable to understanding some observed terminal effects of tsunami.]

Wilson B.W. and Torum A. (1968). The Tsunami of the Alaskan Earthquake, 1964: Engineering Evaluation. Text +16pp. (Appx. C and D). Technical Memorandum No. 25. Vicksburg MI, U.S.A.: U.S. Army Corps of Engineers, Coastal Engineering Research Center. [Engineering exposition of the observed effects of the tsunami; as well as two appendices on the terminal effects of tsunami, such as surge run-up on evenly sloping beaches, including breaking waves, and their damage potential; and presenting practical equations for determining the theoretical flow and force fields of tsunami waves.] Biographical Sketches William Mansfield Adams, Sr., is a retired professor of geophysics and ocean engineering, University of Hawaii, and former director of tsunami research, Hawaiian Institute of Geophysics, Honolulu, Hawaii, USA. He is a seismologist and has earned the degrees of B.A. (University of Chicago), B.S. (University of California at Berkeley), M.B.A. (Santa Clara University), and M.S. and Ph.D. (St. Louis University). He has written two books, edited two more books (one on tsunamis in the Pacific Ocean), and is author of more than 100 scientific articles. He received a Gulf fellowship (at St. Louis University) and a Fullbright grant (to Italy) and holds four US patents related to environmental issues. His experience includes duties performed in Ottawa, Canada (scientific officer), Naples Italy (Fullbright grantee), Moscow (Lomonosov University), Tokyo (UNESCO seismology expert), and in USA: Laramie, Wyoming (chief seismologist), Livermore, California (test director), Honolulu, Hawaii (professor at the University of Hawaii and director of the Tsunami Research Group, Hawaii Institute of Geophysics), and at Indiana University, University of Colorado, and Western Washington University (exchange professor on sabbatical leave). He is at present a consultant and has traveled extensively in Europe, Africa, Asia (including New Zealand and Australia), and Alaska. Jan Malan Jordaan Jr. is a retired civil engineer with experience in hydraulics, principally physical modeling of water-wave phenomena, but also design and modeling of hydraulic structures and investigation of fluvial hydraulic problems. He has earned the degrees of B.Sc. Eng. (Witwatersrand), M.S. (Wisconsin), C.E. and Sc.D. in civil engineering hydraulics (MIT). His professional career includes 28 years with the Department of Water Affairs and Forestry, RSA, and in Namibia, 4 years with the Council of Scientific and Industrial Research, Pretoria, and 4 years in total as associate professor in civil and oceanographic engineering, first at the University of Hawaii and then at the University of Delaware. Prior to that, he helped to create a test facility, and as a research engineer, performed experiments on impulsive waves at the US Naval Civil Engineering Laboratory, Port Hueneme, California. He was responsible for extending the Look Oceanographic Engineering Laboratory of the University of Hawaii, Honolulu, Hawaii, USA, under a National Science Foundation grant, and for establishing hydraulic laboratories at Pretoria, South Africa, and at Windhoek, Namibia, for the Department of Water (and Environment) Affairs and Forestry of South Africa. For the 10 years up to and including 1998, he has been part-time professor of hydraulics at the University of Pretoria, South Africa, and was involved for a total period of one year with assessment of water projects in Bolivia and France. He also visited on official duty other water projects and attended international conferences in Europe, China and South America. He served as a member on advisory committees for the South African Water Research Commission and the South African Institution of Civil Engineers (retired Fellow); and was on the fluid mechanics journal editorial review board of the International Association for Hydraulic Engineering and Research (IAHR), of which he was a member for over forty years. To cite this chapter William Mansfield Adams, Sr. and Jan Malan Jordaan, Jr., (2005), TSUNAMIS AND TSUNAMI WARNING SYSTEMS, in Hydraulic Structures, Equipment and Water Data Acquisition Systems, [Eds.


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Jan Malan Jordaan, and Alexander Bell], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net]
