Foundation, Concrete and Earthquake Engineering

Causes of Tsunami

In 1950s it was hypothesized that larger tsunamis than had previously believed possible may be caused by landslides, explosive volcanic action and impact events when they contact water.

These phenomenons rapidly displace large volume of water, as energy from falling debris or expansion is transferred to the water into which the debris falls at a rate faster than the ocean water can absorbed it. These have been named by people as Mega Tsunami”. But such 

Figure. (Top) Location and parameters of a Norfolk Canyon Slide. Thirty-seven, 10 x10 km simple slides comprise this model. (Panels 2, 3 and 4) Tsunami after 1/2, 1, and 2 hours. Note how long it takes for the waves to traverse the shallow continental shelf.

mechanism may produce a tsunami which is unlike trans-oceanic tsunami caused by some earthquakes due to dissipation of energy and rarely affect coastlines at a large distant due small sea area impact. Sometimes this mechanism can give rise to much larger local shock waves (solitons), like the land slide at Litya Bay 1958, which produce a wave with an initial surge estimated at 524 m. However, an extremely gravitational landslide might generate a so called Mega Tsunami which can have the ability to travel oceanic distances.

The most common and strong cause of tsunami is earthquake. It is not possible that it can generate from movement of Divergent (Constructive) or Conservative Plate Boundaries. This is due to vertical displacement of the water column is impossible on such movements. Tsunami can be generated when Convergent or Destructive Plate Boundaries abruptly move and vertical displacement of overlying water takes place. Earthquake related to subduction zone generate the majority of all tsunami.


Convergent Boundaries

The example includes Storegga during the Neolithic era, Grand Banks 1929, Papua New Guinea 1998.

Subduction Zone

On April 1, 1946 a magnitude 7.8 (Richter scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai’i with a 14 m high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting under Alaska.

Some earthquakes cause sediments to become unstable and subsequently fail. These slumped and as they flowed down slope a tsunami was generated. Another causes of disturbance of sediments may include as a release of gas hydrates ( Methane etc.)

Sometimes Mega thrust earthquakes generates tsunami which can cross the oceans.


1) The Great Chilean Earthquake (19:11 hrs UTC) May 22, 1960 (9.5 Mw)

2) The Good Friday Earthquake, March 27, 1964, Alaska (9.2 Mw)

3) The Great Sumatra-Andaman Earthquake (00:58:53 UTC) December 26, 2004 (9.2 Mw)

But, smaller ( 4.2 Mw) earthquakes in japan can trigger tsunami that can devastate nearby coasts within 15 minutes or less.

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