Tsunami

Causes:

• A tsunami can be generated when convergent or destructive plate boundaries abruptly move and vertically displace the overlying water. It is very unlikely that they can form at divergent or constructive plate boundaries.. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of all tsunamis.
• Tsunamis caused by these mechanisms,unlike the trans-oceanic tsunami, may dissipate quickly and rarely affect distant coastlines due to the small sea area affected. These events can gives rise to much larger local shock waves, such as the landslides at the head of Lituya Bay 1958,which produced a wave with an initial surge estimated at 524 metres. However,an extremely large landslide might generate a megatsunami that can travel trans-oceanic distances, although there is no geological evidence to support this hypotesis.

Warning and prediction:

• A tsunami cannot be precisely predicted even if the right magnitude of an earthquake occurs in the right location. However, there are some warning signs of an impending tsunami and automated systems can provide warnings immediately after an earthquake in time to save lives. One of the most successful systems uses bottom pressure sensors that are attached to bouys. The sensors constantly monitor the pressure of the overlying water column.
• Regions with a high tsunami risk typically use tsunami warning systems to warn the population before the wave reaches land. On the west coast of the United States, which is prone to Pacific Ocean tsunami warning signs indicate evacuation routes.