Seiches

A seiche is a standing wave in an enclosed or partly enclosed body of water. Seiches are normally caused by earthquake activity, and can affect harbors, bays, lakes, rivers and canals. In the majority of instances, earthquake-induced seiches do not occur close to the epicenter of an earthquake, but hundreds of miles away. This is due to the fact that earthquake shock waves close to the epicenter consist of high-frequency vibrations, while those at much greater distances are of lower frequency which can enhance the rhythmic movement in a body of water. The biggest seiches develop when the period of the ground shaking matches the frequency of oscillation of the waterbody.

Vulnerability

Large lakes have many water craft, houseboats, docks, piers, houses and buildings located on or close to their waterfronts. Floating bridges may also be damaged by a seiche. Additional vulnerabilities include water storage tanks, and containers of liquid hazardous materials which are also affected by the rhythmic motion.

Effects

Seiches create a "sloshing" effect on bodies of water and liquids in containers. This primary effect can cause damage to moored boats, piers and facilities close to the water. Secondary problems, including landslides and floods, are related to accelerated water movements and elevated water levels.

Conclusions

Seiches have the potential to cause property damage, and casualties. Public education on seiches is normally included in disaster preparedness classes as a subset of earthquake damage. Although much work has been done on disaster preparedness for the public, local governments, emergency planners, and the citizenry need to recognize the dangers and effects of seiches as an important component of the earthquake hazard.