Introduction to Tsunamis
A tsunami, which is sometimes incorrectly referred to as a tidal wave, is a series of large waves created when either nearshore or undersea earthquakes occur causing sudden movement of the seafloor. The seafloor's movement generates a sudden impulse that causes the water column to displace vertically. The result is a large train of waves. As the wave approaches shallow water, it slows down, but the energy of the wave remains constant. This action causes the wave to increase in height, as high as 30.5 meters (100 feet), in some instances.
Tsunamis . . . How Are They Affecting People?
There is a very short time span for people to evacuate following an earthquake or tsunami warning. Tsunami events affecting the U.S. and its territories have been responsible for almost 470 fatalities and hundreds of millions of dollars in property, infrastructure, transportation, and lifeline damage. The U.S. has not experienced a major tsunami since the Great Alaskan Earthquake at Prince William Sound on March 28, 1964. That event killed 10 people and caused more than $7 million in property damage in Crescent City, California. It caused 106 fatalities and more than $84 million in damage in Alaska.
The Pacific Northwest is vulnerable to tsunamis generated by local and distant earthquakes throughout the Pacific Ocean basin. The greatest tsunami threat for the Pacific Northwest results from earthquakes generated along the Cascadia Subduction Zone (CSZ).
The last major tsunami event in the Cascadia region was the 1964 Alaskan earthquake mentioned above, which produced waves of more than 4 meters (13 feet) at several locations along the west coast. Since that time, several earthquakes in the Pacific Basin have resulted in tsunami warnings and/or measurable events along the west coast, including the April 1992 Cape Mendocino earthquake.
While none of these events have resulted in major damage, the great increase in coastal development in recent decades warrants attention and mitigation for tsunami hazards.
 |
| Newport, Oregon, in 1939 and 2000 |
Tsunami Wave Height Modeling
Researchers have been developing models to show the size of tsunami waves from various earthquake magnitudes.
One model of a large earthquake (magnitude 8.8) along the Cascadia Subduction Zone generated maximum tsunami
wave heights (at 10 meters or 33 feet offshore) of about 6 meters or 20 feet directly adjacent to
the earthquake epicenter, decreasing north and south. Maximum currents
were 3.5 meters per second (m/s) which is about 8 miles per hour.
Recent research at the Oregon Graduate Institute of Science and Technology (OGI) Center for Coastal and Land-Margin Research (CCLMR) and at the National Oceanic and Atmospheric Administration Pacific Marine Environmental Laboratory (NOAA/PMEL) Center for Tsunami Inundation Mapping Efforts (TIME) have both focused on modeling tsunami generation and propagation within the Pacific Northwest. Scenario inundation and propagation maps for the Pacific Northwest and selected coastal communities are available on-line from both research groups. Click on the image below for an animation of computer-modeled tsunami inundation (10.1 MB). The movies can be viewed using QuickTimeŽ with MoviePlayerŽ.
Computer-Generated Inundation Models Showing
Maximum Height of Tsunami Waves for Newport, Oregon
Source: Animations are from Pacific Marine Environmental Laboratory (PMEL).