Tsunami warning systems

Australia's earthquake monitors are used to detect events which may result in a tsunami on Australia's coast and the south west Pacific Ocean. If such an earthquake occurs, Geoscience Australia seismologists immediately notify the Australian Bureau of Meteorology and Emergency Management Australia which subsequently notify other Australian emergency authorities.

Most tsunami occur in the Pacific and Indian Oceans because its boundary, known as the Pacific Ring of Fire, experiences frequent earthquakes and hosts explosive volcanoes.

The Pacific Tsunami Warning System is a network of seismic monitoring stations and sea-level gauges which detects earthquakes and abnormal changes in sea level. Designated centres operate in Hawaii, Alaska and Japan to issue warnings for potential tsunami in the Pacific Ocean.

If a tsunami is detected, coastal areas lying in the predicted path are warned of its approach and expected arrival time which is determined with the use of tsunami travel-time maps. For coastlines particularly prone to tsunami, risk assessments are performed long before a tsunami occurs. An area which may be vulnerable to tsunami is assessed by:

• the likelihood of an event that may cause a tsunami;
• the expected location and size of an event;
• the shape of the seafloor where an event may take place;
• the shape of the coastal land which may be affected by a resulting tsunami; and
• the presence of any headlands or harbours in the region which could cause a tsunami to change direction.

This information is used to predict the potential speed, direction, height and destructiveness of any tsunami that may reach the area. Often, coastal areas that are at risk are part of a funnel-shaped bay or harbour.

Other factors which influence how destructive a tsunami may be include the effect of backwashing from a wave onto a following wave and whether there are any valleys or canyons on the continental shelf.