VERY LOCAL TSUNAMI WARNING SYSTEM ANOTHER CHALLENGE OF INATEWS Masturyono1, Bambang Sunardi2, Suci Dewi Anugrah3 1) Instrumentation, Engineering, and Calibration Centre 2) Research and Development Centre 3) Earthquake and Tsunami Centre ABSTRACT The establishment of the tsunami warning system is based on the fact, that the seismic waves propagate faster then tsunami wave. The tsunami wave arrive in the shore line after the earthquake parameters can be determined, so that there is time left to evaluate the earthquake, whether the earthquake is tsunamigenic or not, disseminated the information or warning to the target area, and finally to do evacuation if necessary. For the tele-tsunami, in which the tsunami will arrive in the beach more then one hour after the origin time of earthquake, generally there is enough time to do all of those processes, so that the warning can be disseminate in 100 % confidence level. For local tsunami, in which the tsunami will arrive in the beach less then one hour, the warning is disseminated in the lower the confidence level. For example, Indonesia Tsunami Warning System (InaTEWS) is designed for local tsunami warning for Indonesian region. Any tsunami-genic earthquake occurs in the Indian Ocean plate boundary, the tsunami wave will sweep the closest shore line within 20-40 minutes after the origin time of the earthquake. The warning is determined just only based on the evaluation of the earthquake parameters and tsunami modeling. It is difficult to add sea level data to increase the confidence level of he warning. Although the confidence level is lower, the tsunami warning could be disseminated. In some cases, especially for the eastern of Indonesia, the tsunami can be generated within inner sea, such as Flores sea, Banda sea, Ceram sea, Maluku sea, and any others. In that cases, tsunami wave will reach the closest shore line within 10 minutes or less. This tsunami may be called as very local tsunami. By evaluating the time line for issuing the tsunami warning, it is clear that very critical to disseminate tsunami warning based on the available technology recently. The effectiveness of the warning is very small, therefore another possibility warning for very local tsunami should be designed. In this presentation, we propose to use natural signs as the warning. As we might know that in general tsunami can be generated by large earthquake. This kind earthquake could be felt strongly by most peoples. This natural sign could be applied as a tsunami warning. The other possibility is to use rather simple technology, as compliment to the natural warning. A very local tsunami warning system can be designed as the following. The warning system consist of two devices, those are a three component broadband seismograph and a local siren. The seismograph can be used to monitor and estimate the magnitude of the local earthquake and the siren can be used to warn the people if the earthquake is possible to generate tsunami. Although, the natural signs and the simple technology could be combine to establish the very local tsunami warning system, the important is to educate people so that they understand the earthquake, tsunami, and how they can save from those disasters. Key word: Tsunami, InaTEWS, Tsunami Preparedness 1. Introduction A tsunami early warning system (TEWS) is a tool for public preparedness in tsunami hazard mitigation. The system should be able to provide the possibility of tsunami generation and disseminate a warning to the society in order to prevent loss of casualties and property. It consists of two components: a network of sensors to detect and predict tsunamis as a half work of the system, and an equal importance of communications infrastructure to issue warning to permit evacuation of dangerous coastal areas as a half one. The TEWS are based on the fact that seismic waves propagate faster then tsunami wave. In the open ocean the wave propagation velocity of tsunamis is about 500 to 1,000 km/h (around 0.14 and 0.28 km/s) while earthquakes has a typical wave speed of 4 km/s (around 14,400 km/h). It’s mean that there is a left time to predict the arriving of tsunami wave into the shore line after the earthquake parameters can be determined. Table 1. The comparison of Tsunami and Earthquake Travel Distance Distance (km) Time Tsunami Earthquake 0 0 0 30 390 12000 60 780 24000 90 1170 36000 The earthquake parameters such as epicenter, hypocenters, magnitude, and also geometrical parameter of the earthquake (slip, strike, dip), become a basic analysis whether the earthquake is a tsunamigenic or not, and whether the system has to issue a warning to the people in the coastal area. Unfortunately, it is not easy to detect a tsunami based on earthquake parameters only. This approach often produces many more false alarms than verified warnings. In the current operational paradigm, the seismic alerts are used to send out the watches and warnings. Then, data from observed sea level height (either shore- based tide gauges or DART buoys) are used to verify the existence of a tsunami. At least, there are 3 kinds of Tsunami due to its arrival time: Distance Tsunami, Local Tsunami and Very Local Tsunami. A far field tsunami or a distance tsunami is referred to the tsunami event of the very far away source to the coastal effected by tsunami. In this case the tsunami wave will come to beach in 1 hour later even more, and still have enough time to verify the high wave based on the dart buoy and even the tide gauge as we can see in the Distant Tsunami Warning Chain. Figure 1. Distance tsunami modeling Figure 2. Diagram of distant tsunami warning chain The unique position of Indonesia geologically causes the system has to be designed as a local Tsunami Early Warning System. The subduction zone of Indonesian area extends from the north western corner of Sumatra to Flores the eastern part of Indonesia. Should a tsunami occur in the off coast of Indonesia, the waves will reach the coast within 20 minutes even least than it. This situation makes the system has to issue warning not more than 10 -15 minutes, in order to give a little time for people to evacuate the dangerous area. A new approach of the fast and reliable determination of strong earthquakes has been tried to be applied into the InaTEWS. The InaTEWS is an aggregate system of all of sensor monitoring systems and the numerical modeling of tsunamis which can be seen in the situation assessment of the GUI system. All of the information obtained from all sensor monitoring networks are collected by a system, known as Decision Support system (DSS).Unfortunately, The InaTEWS is not an easy system practically. The direct incorporation of abroad variety of different sensors for a more precise determination of a tsunami to reduce a false alarm is a big challenge. Figure 3. Local tsunami modeling a) b) Figure 4. Diagram of local tsunami warning chain Due to the generating of earthquake tsunamigenic, the eastern part of Indonesia is a very unique geological situation. The fault positions in that area forms a very complicated formation that the tsunami can be generated within inner sea, such as Flores sea, Banda sea, Ceram sea, Maluku sea, and any other. This situation makes tsunami wave will reach the closest shore line within 10 minutes or less as a very local tsunami event. Meanwhile the performance of InaTEWS has no capability to process a very quick tsunami warning less than 5 minutes. It is purposed to use the natural signs for people in that area to evacuate themselves. Therefore the role of tsunami preparedness education is an importance factor to build a community preparedness of tsunami hazard 2. The Progress of InaTEWS The big catastrophic tsunami 2004 Sumatra event is one of the motivations to develop the Indonesia Tsunami Early warning System (InaTEWS) that is officially handed over to BMKG (Meteorological Climatological and Geophysical Agency of Indonesia).The establishment of InaTEWS is still far away from the final design. The earthquake monitoring sensor network is the first system to assess the Tsunami even. But, not every earthquake generates a tsunami. For this reason it must be determined at sea whether or not an earthquake has actually triggered the deadly wave. For this purpose underwater measuring units are usually used where a pressure gauge is employed to record a tsunami. Nowadays, tsunami early warning information in Indonesia is mainly based from earthquake monitoring which is controlled from the InaTEWS seismic network, located at BMKG Headquarters, Jakarta. It is difficult to add sea level data to increase the confidence level of the warning. Although the confidence level is lower, the tsunami warning could be disseminated. The full sensor configuration of InaTEWS will consist of 160 broadband seismographs and 500 accellerographs for seismic observation, 40 GPS, 80 tide gauges and 23 Dart-buoy for observing sea-waves. In 2007, it was the first time for the Indonesian tsunami early warning, InaTEWS, successfully provided early warning on the occurrence of tsunami at Bengkulu on 12 September 2007, however, the performance of InaTEWS is not gratified yet. During 2007 to January 2009, The InaTEWS had already issued 21 warnings, but only 5 warnings can be categorized as a true warning. It means that most of the warnings are categories as a false warning. Figure 5. Numbers of warning issued since January 2007-January 2009 (Fauzi, 2009). 3. The Examples of Very Local Tsunami in Indonesia The Flores Tsunami (1992) is one of the examples of a very local tsunami event in Indonesia, particularly in the eastern part of Indonesia. The simulation shows that the wave reach the closest shoreline area about 5 minutes later after the earthquake happened. According to the seismicity map of North Sulawesi and its surrounding area, the earthquake sources are dominantly located in the inner part of the seas. Those condition makes the sources are surrounded by many coastal areas of some islands in a very close distance. In addition most of those source locations are the earthquake sources that may be predicted as a tsunamigenic earthquake with M>5.0 and D<60 km. . Therefore, it is understood that most of tsunami events in this area are categorized as a very local tsunami. Figure 6. Flores tsunami modelling Figure 7. Seismicity map of North Sulawesi Figure 8. Seismicity map of eastern part of Indonesia with M>5.0;D<60km Figure 9. Tsunami modelling of 12th February 2009 earthquake One of the recent example of a local tsunami event in the eastern part of Indonesia is an earthquake that occurred on February 12th 2009. The location is taken a part in the northwest sea of Halmahera. This earthquake is predicted as a tsunamigenic earthquake. The simulation shows that the tsunami wave will reach the closest beach in 5 minutes after the earthquake. 4. The Role of Tsunami Preparedness Education Tsunami preparedness means all preparation activities regarding a tsunami hazard event to improve a community’s capabilities to respond to and recover from tsunami. In the term of the subject who involved, Preparedness has a little difference from mitigation activities. Preparedness usually is a result of individual organizations while mitigation projects tend to be jurisdictional policies. The activities of Tsunami preparedness education include: 1. Training programs for response personnel 2. Tsunami detection and warning systems 3. Identification of evacuation routes and shelters 4. Public education The public education might be considered as a key of those activities. Education programs are the only way to prepare community members to evacuate when they observe natural warning signs. The goal of public outreach programs is not only to share basic information about when, how and where to evacuate but also to have people recognize tsunamis Due to the very local tsunami event that mostly occurred in the eastern part of Indonesia, it is quite difficult to rely on the capability of InaTEWS only. The portion of education approach of tsunami preparedness in order to inform the sign of tsunami hazard event has to be maximized than technological approach of InaTEWS. The diagram of Solution Approach shows the resolving of all kinds of tsunami event using a combination of technological approach and cultural and natural sign approach in different portion. For the very local tsunami it is suggested that using cultural approach is more reliable than using technological approach. Therefore it is advised that the people should evacuate themselves as soon as they recognize the natural sign without waiting for a warning issued by TEWS. TECHNOLOGICAL CULTURAL & NATURAL SIGN VERY LOCAL LOCAL DISTANCE Figure 10. Solution approach Figure 11. Diagram of very local tsunami Warning Chain People in Simeuleu island of Banda Aceh is one of the best example of cultural approach implementation when the tsunami 2004 occurred as a local tsunami. A number coastal villages in that area evacuated and survived themselves because of the cultural tradition of their communities which emphasized immediately running to high ground after feeling a strong earthquake. The first tsunami wave arrived at Simeulue Island only 8 minutes after the earthquake, destroying every structure in the community. No casualties in the village because everyone understood the natural sign and knew to grab their children and help the elderly to a predetermined area on high. 5. Understanding of Natural Signs The lack of facilities of tsunami preparedness activities in the eastern part of Indonesia requires the tsunami natural sign understanding as an aspect that has to be stressed in the term of tsunami preparedness education. Some information regarding the tsunami natural sign that should be informed to the society are: 1. A big earthquake will shake strongly, that can be felt by many people. This sign should be accept as a tsunami warning that can be used to start doing self evacuation by staying away from the coastal area. 2. If earthquake felt and or nothing felt but the sea level draw seaward abnormally, is also indicate the tsunami will come. People may start to move away from the coastal area. 6. Conclusion 1. The INATEWS is designed for local tsunami, therefore the implementation for eastern Indonesia should be modified. 2. The eastern Indonesia region, mostly will deal with be deal with the very local tsunami, therefore the community preparedness programs by stressing on the understanding of natural signs should be started. 3. To make the system more effective, there are more tsunami mitigation programs using cultural approach should be done consistently. References Fauzi, 2009, Interoperability of Indonesia Tsunami Early Warning and Dissemination system The German Indonesia Tsunami Warning System (report), 2008 www.wikipedia.com McAdoo, Dengler, Prasetya, and Titov. Smong: How an Oral History Saved Thousands on Indonesia’s Simeulue Island during the December 2004 and March 2005 Tsunamis. (English). Natural Tsunami Warning, Course material of Tsunami Science and Preparedness Training, 2007, Seattle.