Very Local Tsunami Warning System, Another Challenge of InaTEWS

8/6/2019 Very Local Tsunami Warning System, Another Challenge of InaTEWS

http://slidepdf.com/reader/full/very-local-tsunami-warning-system-another-challenge-of-inatews 1/9

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 theearthquake 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 tsunamigeneration 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

TimeDistance (km)

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 whetherthe 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 triedto 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 systems3. 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.



VERY LOCAL LOCAL DISTANCE

CULTURAL &

NATURAL SIGN

TECHNOLOGICAL

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 approachimplementation 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 Indonesiarequires 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 Disseminationsystem

The German Indonesia Tsunami Warning System (report), 2008

www.wikipedia.comMcAdoo, 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.

Very Local Tsunami Warning System, Another Challenge of InaTEWS

Documents

Transcript of Very Local Tsunami Warning System, Another Challenge of InaTEWS