Tsunami Dynamics

types of waves: displacement

waves in an ocean/lake that result from a displacement of water caused by shifts in basin floor, may be seismogenic, heights up to/over 100 km when subaerial/submarine landslides are involved, and wavelength of 1000s of meters when caused by seismicity (tsunamis)

types of waves: tidal

waves resulting from the gravitational force between Earth & Moon/Sun, period of two waves per day, heights of 17m in Bay of Fundy, water is being pulled

types of waves: wind-generated

waves during storm surges, short periods, lower amplitudes and displacements

types of waves: tsunamis

large body wave generated in ocean/large late, long wavelength, high speed, low amplitudes in deep water but increase towards the shore, periods of 10-60 mins which can shorten near shore

wave speed

sqrt(gravity x depth), good for shallow (< 1 km) water

seismogenic tsunamis

larger movement causes larger tsunamis; however, this isn't always the amplification of wave height

causes for wave height amplification

shoaling, focusing, resonance

shoaling

as wave approaches decreasing water depths, the leading wave will slow, but water behind will build up and increase wave height

focusing

as wave enters shallowing bathymetry along an irregular coast, the wave front bends due to refraction of the waves, and they converge onto each other

resonance

if period of the oscillation is in phase with tsunami wave, a larger amplitude will result

triggers of displacement waves

seismogenic, submarine/subaerial landslides, submarine volcanic eruption, meteorite impact

dampening

a reduction of amplitude over time resulting from friction, inversely proportional to wavelength

longer wavelengths mean...

higher water for longer periods

why do tsunamis maintain energy over long distances?

because they have long wavelengths

countermeasures against tsunamis (2011 Japan)

offshore and onshore tsunami barriers, natural planted tree barriers, vertical evacuation buildings, periodic evacuation training