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Tsunamis can occur when an underwater earthquake rapidly displaces massive amounts of water, leading to a large, long wave that builds in intensity as it crosses the ocean. When it reaches land it ...
A 2021 map shows the impact of a tsunami hitting the San Fransisco area - and the devastation it could cause. The map was thrust back into the spotlight Thursday when a 7.0-magnitude earthquake ...
Diagram showing how earthquakes can generate a tsunami. Tsunamis in lakes can be generated by fault displacement beneath or around lake systems. Faulting shifts the ground in a vertical motion through reverse, normal or oblique strike slip faulting processes, this displaces the water above causing a tsunami (Figure 1).
While tsunamis travel at between 500 and 1,000 km/h (around 0.14 and 0.28 km/s) in open water, earthquakes can be detected almost at once as seismic waves travel with a typical speed of 4 km/s (around 14,400 km/h). This gives time for a possible tsunami forecast to be made and warnings to be issued to threatened areas, if warranted.
Smaller (M w 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can devastate stretches of coastline, but can do so in only a few minutes at a time. Landslides The Tauredunum event was a large tsunami on Lake Geneva in 563 CE, caused by sedimentary deposits destabilised by a landslide.
Both surface deformation and faulting and shaking-related geological effects (e.g., soil liquefaction, landslides) not only leave permanent imprints in the environment, but also dramatically affect human structures. Moreover, underwater fault ruptures and seismically triggered landslides can generate tsunami waves.
The thrust faults responsible for megathrust earthquakes often lie at the bottom of oceanic trenches; in such cases, the earthquakes can abruptly displace the sea floor over a large area. As a result, megathrust earthquakes often generate tsunamis that are considerably more destructive than the earthquakes themselves.
A tsunami earthquake can be defined as an undersea earthquake for which the surface-wave magnitude M s differs markedly from the moment magnitude M w, because the former is calculated from surface waves with a period of about 20 seconds, whereas the latter is a measure of the total energy release at all frequencies. [2]