M A S T E R P A G E
Tsunami Event Reports
2.4g
1.
On July 12, 1993, the Hokkaido-Nansei-Oki earthquake of magnitude 7.8 produced one of the largest seismic
sea waves in Japan’s history. The tsunami hit the Okushiri coast within five minutes after the main shock, causing
waves at the shoreline between 15 and 30 m high. The town of Aonae on the island of Okushiri suffered extensive
damage. At least 185 people were killed, with property damage estimated at $600 million.
2.
The Prince William Sound, or Anchorage, Alaska, earthquake of March 27, 1964, caused seismic sea waves
generated by an underwater landslide. At Valdez, the earthquake triggered a landslide that deepened the harbor by
as much as 100 m in one place and caused a tremendous tsunami. In addition, the earthquake uplifted the sea floor
by as much as 4 meters. The tsunami killed 119 people in Alaska, Hawaii, and California and caused over $282
million in damage.
3.
On April 1, 1946, at 53.5º north and 163º west, 130 km southeast of Unimak Island, Alaska, a large earthquake
occurred 4,000 m below the ocean surface in the Aleutian Trench, causing an undersea landslide. Four and one
half hours later, a tsunami reached Oahu, Hawaii, after traveling 3,600 km at 800 km/hr. Water rose 12 m above
the high tide line on Oahu and 18 m on Hawaii (the “Big Island”). This seismic sea wave demolished 488 homes
and damaged 936 others, with property loss estimated at $25 million and 173 people killed.
4.
An earthquake on the ocean floor may also cause a compressional wave that can severely damage ships close to
the epicenter of the event. Even though we consider fluids as non-compressional in systems like automobile
brakes, compressional waves can travel in seawater under the tremendous pressures and accelerations of the water
in underwater seismic events. Ships struck by these waves report an experience similar to running aground or
striking another vessel.
In 1969, a magnitude 8.0 earthquake west of Gibraltar caused compressional waves that struck the 32,500-ton
tanker
Ida Knudsen
, sailing in 4,900 m of water. The tanker was 35 km from the epicenter of the seaquake and
suffered so much damage that at first it was declared a total loss. The ship was later extensively rebuilt.
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