sea l evel The height of the sea at a given time measured relative to some datum, such as mean sea level.

shallow water velocity or tsunami velocity The velocity of an ocean wave whose length is sufficiently large compared to the water depth (i.e., 25 or more times the depth) can be approximated by the following expression: c =Sqrt(gh) Where: c is the wave velocity g the acceleration of gravity h the water depth. Thus, the velocity of shallow-water waves is independent of wave length L. In water depths between ½L and 1/25 L it is necessary to use a more precise expression: c =Sqrt((gL/2π )[tanh(2 π h/L)]) Wave Height and Water Depth: in the open ocean a tsunami is less than afew feet high at the surface, but its wave height increases rapidly in shallow water. Tsunami wave energy extends from the surface to the bottom in the deepest waters. As the tsunami attacks the coastline, the wave energy is compressed into am much shorter distance creating destructive, life threatening waves.

Sieberg tsunami intensity scale A descriptive tsunami intensity scale which was later modified into the Sieberg-Ambraseys tsunami intensity scale described below (Ambraseys 1962).   Modified Sieberg Sea-wave Intensity Scale 1. Very light. Wave so weak as to be perceptible only on tide-gauge records. 2. Light. Wave noticed by those living along the shore and familiar with the sea. On very flat shores generally noticed. 3. Rather strong. Generally noticed. Flooding of gently sloping coasts. Light sailing vessels carried away on shore. Slight damage to light structures situated near the coasts. In estuaries reversal of the river flow some distance upstream. 4. Strong. Flooding of the shore to some depth. Light scouring on man-made ground. Embankments and dikes damaged. Light structures near the coasts damaged. Solid structures on the coast injured. Bid sailing vessels and small ships drifted inland or carried out to sea. Coasts littered with floating debris. 5. Very strong. General flooding of the shore to some depth. Quay-walls and solid structures near the sea damaged. Light structures destroyed. Severe scouring of cultivated land and littering of the coast with floating items and sea animals. With the exception of big ships all other type of vessels carried inland or out to sea. Big bores in estuary rivers. Harbor works damaged. People drowned. Wave accompanied by strong roar. 6. Disastrous. Partial or complete destruction of man-made structures for some distance from the shore. Flooding of coasts to great depths. Big ships severely damaged. Trees uprooted or broken. Many casualties.

significant wave height significant wave height The average height of the one-third highest waves of a given wave group. Note that the composition of the highest waves depends upon the extent to which the lower waves are considered. In wave record analysis, the average height of the highest one-third of a selected number of waves, this number being determined by dividing the time of record by the significant period. Also characteristic wave height.

spreading When reference is made to tsunami waves, it is the spreading of the wave energy over a wider geographical area as the waves propagate away from the source region. The reason for this geographical spreading and reduction of wave energy with distance traveled, is the sphericity of the earth. The tsunami energy will begin converging again at a distance of 90 degrees from the source. Ofcourse tsunami waves propagating across a large ocean undergo other changes in energy configuration due to refraction, primarily, but geographical spreading is also very important depending upon the orientation, dimensions and geometry of the tsunami source.