Examples of Tsunamis generated by Earthquakes

April 1, 1946 - A magnitude  7.3  earthquake occurred near Unimak Island in the Aleutian Islands west of Alaska, near the Alaska Trench.  Sediment accumulating in the trench slumped into the trench and generated a tsunami.  A lighthouse at Scotch Gap built of steel reinforced concrete was located on shore at an elevation of 14 m above mean low water.  The first wave of the tsunami hit the Scotch Gap area 20 minutes after the earthquake, had a run-up 30 m and completely destroyed the lighthouse.  4.5 hours later the same tsunami reached the Hawaiian Islands after traveling at an average speed of 659 km/hr.  As it approached the city of Hilo on the Big Island, it slowed to about 47 km/hr (note that even the fastest human cannot run faster than about 35 km/hr) and had a run-up of 18 m above normal high tide. It killed 159 people (90 in Hilo) and caused $25 million in property damage.

May 22, 1960 - A magnitude 8.6 earthquake occurred  along the subduction zone off South America.  Because the population of Chile (movie clip) is familiar with earthquakes and potential tsunamis, most people along the coast moved to higher ground.  15 minutes after the earthquake, a tsunami with a run-up of 4.5 m hit the coast.  The first wave then retreated, dragging broken houses and boats back into the ocean.  Many people saw this smooth retreat of the sea as a sign they could ride their boats out to sea and recover some of the property swept away by the first wave.  But, about 1 hour later, the second wave traveling at a velocity of 166 km/hr crashed in with a run-up of 8 m.  This wave crushed boats along the coast and destroyed coastal buildings. This was followed by a third wave traveling at only 83 km/hr that crashed in later with a run-up of 11 m, destroying all that was left of coastal villages.  The resulting causalities listed 909 dead with 834 missing.  In Hawaii, a tsunami warning system was in place and the tsunami was expected to arrive at 9:57 AM.  It hit at 9:58 AM and 61 people died, mostly sightseers that wanted to watch the wave roll in at close range (obviously they were too close).  The tsunami continued across the Pacific Ocean, eventually reaching Japan where it killed an additional 185 people.  March 27, 1964 - The Good Friday Earthquake in Alaska had a magnitude of 8.5 on the Richter Scale.  This earthquake also occurred along the subduction zone, and as we saw in our study of earthquakes, caused deformation of the crust where huge blocks where dropped down as much as 2.3  m.  Because the coastline of Alaska is sparsely populated, only 122 people died from the tsunami in Alaska.  With a tsunami warning system in place in Crescent City, California, all the townspeople moved to higher ground.  After watching four successive waves destroy their town, many people returned to the low lying areas to assess the damage to their property.  The fifth wave had the largest run-up of 6.3 m and killed 12 people. September 2, 1992 - A magnitude 7 earthquake off the coast of Nicaragua in Central America occurred along the subduction zone below the Middle America Trench. The earthquake was barely felt by the residents of Nicaragua and was somewhat unusual.  A 100 km-long segment of the oceanic lithosphere moved 1 m further below the over riding plate over a period of two minutes.  Much energy was released but the ground did not shake very much.  Seawater apparently absorbed some of the energy and sent a tsunami onto the coast.  Residents had little warning, 150 people died and 13,000 people were left homeless.