Experience in Nicaragua on the develpment of a Tsunami Warning System
Wilfried Strauch (Instituto Nicaragüense de Estudios Territoriales)
On september 2, 1992, around 8 PM local time, 4 to 10 m high tsunami waves killed at least 170 people all along the Pacific Coast of Nicaragua. The earthquake which caused the Nicaraguan tsunami, had the speciality that the seismic effects were very small though the magnitude of the event was around 7.6. It was a so called slow earthquake which generates most of its energy in the long period range, on slow oscillations. So, the seismic shaking could not serve as a early warning for the people on the coast.
In 1992, there was no seismic network in Nicaragua, no communications facilities with the towns and villages at the Pacific Coast, no trained personnel, and people in Nicaragua before the disaster were not aware that the tsunami hazard exists. Our seismological department had not even telephone, fax or email to be able to receive or emit information. Nicaragua was not a member of the International Tsunami Warning System in the Pacific Ocean and would not receive warning messages from Hawaii Warning Center. So, a situation very similar to what we see now in South Asia.
After the 1992 tsunami we have, step by step, developed a National
Tsunami Warning System.
First we became member of the Pacific Tsunami Warning System. After 1992, Nicaragua participated in all regular meetings of ITSU. We receive regularly the tsunami warnings emitted by Pacific Tsunami Warning Center and observe the web sites of other centers of the system. In case of very strong earthquakes in the Pacific Basin, especially en relatively near distances as in Colombia or Mexico, Guatemala, El Salvador Costa Rica, we follow the News reports and use our own contacts to get informations about possible tsunamis to decide whether a tsunami warning is necessary or not. Contacts to the Radio amateurs are important, too.
Then we developed a conventional seismic network which is now the largest network in Central America. We did this in cooperation with Norwegian, Swedish, German, Swiss and American institutions and together with other countries in Central America. Later we got digital seismic equipment, especially seismic broad band stations, necessary to detect the long period seismic waves which are used to calculate the correct magnitude of very strong earthquakes. We have trained our staff for the seismic monitoring and the maintenance of the network. There is a well organized seismic service working around the clock. Any seismic event is processed immediately. We report the parameters of the seismic events in Nicaragua and Central America regularly within 15 minutes after occurrence. Small events are only reported in our web page http://webserver2.ineter.gob.ni/geofisica/sis/monitor.html. Notifications on stronger events are reported automatically via email and fax to about 70 institutions, mass media or persons in Nicaragua and Central America.This capacity to report seismic events very fast is important for the tsunami warning.
If we detect an earthquake with a magnitude above 7.0 which occurred near the Pacific coast of Nicaragua or Central America we would emit a tsunami warning to the Civil Defense Organization in Nicaragua. In the frame of a project on tsunami warning financed by Switzerland they installed in 1996 a radio communication system to connect the towns and villages on the Pacific coast. The radios are installed in the houses of members of the local administration. The local people have to inform their population by their own means, i.e. bells, loud speakers, cars. The tsunami warning message would also be distributed via the mass media and it can be hoped that a number of people have their radio on to hear the message.
Our system is certainly not yet perfect. Several years ago Civil Defense of Nicaragua elaborated a project proposal for the installation of sirens along the coast but could not get funding as the costs are rather high. We are executing in 2005 a pilot project with Civil Defense and CARE to test the use of sirens on a local scale. We are also aware that in the case of a very strong earthquake our personnel might fail to work well. Thus we are now developing seismic facilities and automatic computer procedures which would emit the warning messages. We are also seeking more regional cooperation. Then, after a time people will tend to forget the 1992 tsunami. So, education of the population, especially the young people, will have a high priority.
It should be mentioned that our tsunami warning system was installed using much infrastructure financed for other purposes and vice versa parts of the tsunami warning system are used for other things. The seismic network works as well for seismic and volcano monitoring, the radio communications system helps the local population in case of any other accident or problem. Thus it is easier to justify the costs. It is hard to get money for mitigation measures for a hazard which produces a possible disaster every 1000 years
We participated also in several projects to investigate the tsunami hazard for Nicaragua. Geophysical studies carried out with German and American Universities delivered bathymetric data important to study the propagation of tsunami waves. From these data we learned also that tsunamis can be caused in Nicragaua by giant submarine landslides in the Pacific Ocean off the coast of Nicaragua. Last year we started a project to make numerical simulations of tsunami and to generate tsunami hazard maps. This project is financed by the Japanese government and carried out together with Japanese consultants. After finishing this project we will be able to give the local authorities maps which indicate the most hazardous zones and save places.
Taking into account that Nicaragua is actually the second poorest country in the Americas I think we have done a lot to avoid the repetition of a tsunami disaster or at least to mitigate it. Funding was obtained from many national and international sources and we cooperate with institutions and scientists from allover the world.
We have also pushed the development of a regional tsunami warning system in Central America. Actually, the interest in the other countries of the region was not as high as in Nicaragua. Last year, and based on the experience in Nicaragua, INETER sent a proposal to the geosciences institutions in the region and CEPREDENAC (Center of Prevention and Reduction in Central America) to form a regional tsunami warning system. The proposal was also presented by representatives of Nicaragua and El Salvador to ITSU (International Coordination Group for the Tsunami Warning System in the Pacific) in the name of the region. The proposal was accepted and ITSU supports now the formation of a regional tsunami warning system in Central America.
We propose that each country develops its own national tsunami warning system, based on the existing infrastructure as seismic network communications systems, etc. These national systems interact, exchange experiences, make use of the different capacities of the neighboring countries, for instance each country can use data from seismic stations in the other countries. In case of a strong tsunami each national warning center emits its warning message and sends it to the other centers and the emergency commissions of all countries. From there the messages would be re transmitted over adequate channels to the population. That way there is a high degree of redundancy in the system which is necessary to overcome the impact of a very large natural phenomenon. If one national system fails there is hope that others in the region success to send their message to the people. There will be a regional meeting, in February 2005, to discuss the situation in Central America what concerns tsunami hazard and tsunami warning.