Earthquakes & Tsunami

Indonesia with its complicated tectonic setting, crossed by the boundaries of three tectonic plates is highly endangered by earthquakes. The destructive powers of this hazard are well known to the public:
The shaking ground can cause buildings and bridges to collapse and disrupt gas, electric, and phone services. Especially in Indonesia earthquakes also trigger landslides and huge, destructive ocean waves called tsunami. The following overview about some resent disasters gives an impression about Indonesia's exposure to earthquakes:

What is a Tsunami?

The word "Tsunami" is derived from Japanese. Literally translated it means "great harbor wave". This is because Tsunami waves can reach heights of around 40 m when they proceed to coastal areas with lower water depths. The term contains a suitable description for one of the most threatening rapid onset natural hazards in the world.
Tsunami can be classified in local and distant (teleseismic) Tsunami according to the distance from the point of origin to the affected areas. But only a few major Tsunami traveled across the whole Pacific Ocean damaging distant areas hours after the initial event took place.

What triggers a Tsunami?

All these effects cause a disturbance of the whole water column above the original place of action (for example above the Earthquake zone). The disturbance is propagating like a wave in all directions but with a speed of up to 800 km/h. In contrast to wind generated waves the Tsunami affects the whole water column transporting a high amount of energy. On the surface of deep oceans Tsunami waves have only the dimensions of normal wind waves (e.g. around 1 m wave height). But as they approach the continental shelf and finally coastal areas where the water depth is rapidly decreasing, the wave can reach heights of up to 30 m.

What are the potential effects of Tsunami?

On the surface of deep oceans Tsunami have almost no effects, as their wave height is similar to wind waves. The crew of a ship will not be able to recognize a Tsunami in the open sea.
In coastal areas the energy of the Tsunami wave is forced into lower water depths, which may result in up to 40 m high wave crests. This huge wave can dislocate coral reef parts weighing more than 100 tons and take ships hundreds of meters inland. The initial force of the Tsunami can uproot trees and destroy all kinds of structures on land (like houses, bridges, streets…). An additional effect is that the Wave can take up lots debris from coastal areas, which is then smashed to inland areas with an immense power, turning for example tree branches into perilous projectiles. Another effect is the strong water current induced by the oncoming wave as well as the receding water. This can tear objects and people to the sea and cause heavy erosion in the affected areas. In addition to that it is characteristic for Tsunami to occur in wave cycles, which means it is possibly not finished after the first devastating wave. Smaller or even more powerful waves may proceed to the coast in the following hours after the first wave arrived.

Where do Tsunami occur?

Worldwide around 82 % of all Tsunami are triggered by earthquakes. This has a major effect on the distribution of Tsunami around the world. Tsunamis are usually bound to the vicinity of active continental plates where most of the Earthquakes are initiated. This leads to a characteristic distribution of Tsunami around the so called "Pacific Ring of Fire" covering the circumpacific coasts from South to North America, Northeast to Southeast Asia up to Northern Australia and Northern parts of New Zealand.
Indonesia with its complicated tectonic setting (including the active boundaries of three tectonic plates) and its vast coastal areas has also a high susceptibility to Tsunami. According to BRYANT (2001) 12% of all Tsunami in the Pacific Region during the last 200 years hit the coasts of Indonesia. In fact Indonesia is ranked second behind Japan in the list of countries with a high frequency of Tsunami in the Pacific.

When and where did Indonesia experience major Tsunami in the last decade?

What can be done to mitigate potential Tsunami effects in communities?

Education
Dissemination of information about Tsunami in primary and secondary school 
contributes to the understanding  of  the    phenomenon.  This  should  have
positive effects to a growing public awareness about Tsunami.

Planning
Guidelines   can  prevent people  from settling  in   endangered   areas. The 
application  of building codes can protect people and their belongings   from 
potential damage.

Risk  mapping identifies areas of potential loss and  damage    concerning a 
given Tsunami event. It helps to keep sensitive structures e.g. for emergency
response out of the threatened areas.

Early warning systems can provide crucial information for the evacuation  of 
threatened areas.

Preparedness
A prepared local community will be less vulnerable to Tsunami effects as the
people will know what to do if there are any signs or precursors of a Tsunami 
(for example: Move to higher ground after severe ground shaking    due to an 
Earthquake).

Which are the project activities related to Tsunami?

The Project "Mitigation of Geohazards" is dealing with the tsunami risk in the project area of Maumere (Kabupaten Sikka), Flores , where a major Tsunami occurred in 1992. It is planned to map the tsunami threatened areas, assess the potential economic damage as well as to develop and implement guidelines for the prevention of future tsunami effects.
So far a fact-finding mission to Maumere was conducted in Mai contacting the related local decision makers and institutions