possibility of implementing natural coastal fortress in sulawesi island

8/6/2019 Possibility of Implementing Natural Coastal Fortress in Sulawesi Island

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ASCOT Research International Journal, Volume 3, December 2010

1

Possibility of implementing Natural Coastal Fortress in Sulawesi Island

Due to Tsunami Impact

Achmad Yasir Baeda1

and Karuniawan Puji Wicaksono

ABSTRACTSulawesi Island which surrounded by several large tectonic plates and

several small ones, has been struck 270 times by earthquakes with magnitude

more than 5.0 over the past 33 years. This number of earthquake occurrences

tends to become higher due to the rising activity of Sunda fault after the big

earthquake on December 26th

2004.

The goal of this study is to analyze the possibility of implementing natural

coastal forest as a fortress on Sulawesi Island to mitigate tsunami impact. Data

was collected from Global CMT and several previous research projects. Method

used for the analysis was based on intersection of both hazards characteristics,

which were earthquakes and tsunami, with coastal forest as the most possible

countermeasures. The authors suggest that the connection function for the

possibility analysis of implementation would be strongly correlated with

dimension of the coastal forest, especially the length of the shore line. In the case

of Sulawesi Island, the authors found that there still a small percentage of coastal

forest existed with the width minimum. It means that there was a possibility of

implementing natural coastal forest as fortresses from tsunami impact, basic on

the existing forest; but will not cover all the tsunami prone areas in the island,without any strong efforts of extending reforestation activities.

Keywords: earthquake, tsunami, coastal forest

INTRODUCTION

Situated in the South East Asia tectonic regimen, Indonesia is well known

as the most seismically active country in the world (Aydan, 2008). It surrounded

by Indo-Australian plate in the southern part which subduct beneath the Eurasian

plate, with five big islands and several peninsulas, Indonesia has experienced

thousands of earthquakes and hundreds of tsunamis over the past four hundred

years. Sumatera and Jawa are two of the most vulnerable islands due to tsunami

impact since their position which directly in front of the subduction zone of Indo-

Australian Plate. Papua and Sulawesi had also experienced several tsunamis, even

though were not as often as those first two. But in the case of potential area for


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earthquake and tsunami occurrence, Sulawesi is in the most susceptible to all. Not

only because of its complex faults system but also because these last few years

there were very small amount of sea quakes occurred in the region, making it the

most potential area of earthquakes and tsunamis occurrences after Jawa and

Sumatera.

Geographically, Sulawesi Island lays on 5.36N-7.48S and 117.02-125.74E is one of the most secure islands of ocean hazards in Indonesian

archipelago due to its indirect position from two oceans, the Pacific and the

Indian. Sulawesi which divided into six provinces has several small archipelagos,

making it one of the big islands in Indonesian archipelago that had very long

shoreline. Unfortunately, this also means that Sulawesi is vulnerable to sea

hazards events, such as big waves or tsunami.

Thus, Sulawesi urgently needs some kind of prevention for protecting its

coast. There are several options for protection scheme, i.e. early warning system,

sea walls, breakwaters and coastal forest. In the case of natural environment

issues, the most reasonable scheme is to establish coastal forest. But before it was

implemented, there should be a prior analysis of it. The goal of this study is

finding the main reason and why the coastal forest can be implemented as

protection against tsunami on Sulawesis coasts.

MATERIALS AND METHODS

For the analysis, several data sources were utilized, i.e. Sulawesis fault

system, earthquakes and tsunami records, coastal vegetations, and others. All ofthe data will be taken into account for reaching the goal.

Overview of Sulawesis Fault System

Geologically, in the beginning, Miocene era Sulawesi was formed from

two islands, one lied at magmatic arc of Mindanao and the other was at the

subduction zone of Caroline Plate to Eurasian Plate. From that era until this time,

the first island was forming North and South Arm (Fig. 1). Meanwhile, the other

one from the subduction zone was forming Southeastern Arm and East Arm.

Since then until late Pliocene era, the Pacific plate pushed them towards

Kalimantan Island, making them joined together in central part of Sulawesi. But

at Quartenary until now, the forming island drifted away from Kalimantan Island

due to sea-floor that spreading along the east-west Paternoster fault. This

formation process makes Sulawesi as an island that had a complicated fault


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Fig. 1. Sulawesi Island with four parts

system, with several types of faults connected with each other literally and

sometimes can produce big quakes (Katili, 1978).

There are at least 7 faults which actively interact to each other in Sulawesi

(Fig. 2), i.e. Paternoster, Walanae, Palu-Koro A and B, Matano A and B, Balantak

and several small faults from small plates (Guntoro, 1999). The earthquakes also

produce by the movement of several small thrust, especially from east to westpart. In a contrary, there are also movements from three spreading-center at

Makassar Basin; two in the North part and the other in the South part (Prasetya et

al, 2001).

The Paternoster fault which divides Makassar

Basin into South and North part is a strike-slip

transform fault. It also an extension of the Walanae

faults. Meanwhile, Walanae started at the south end

of South Arm and goes up until it reached

Rantekambolas peak at Toraja, where it met thePaternoster fault. Even though these faults are strike-

slips which have small percentage of producing big

quakes, statistically Paternoster and Walanae have

produced more tsunami than other fault in Sulawesi

geologic system. It means that Paternoster and

Fig. 2. The 7 faults attached in Sulawesi along with

all the epicenter of earthquakes from 1976-2009

Figure 3.Simplified geological sketh

map (Villeneuve et al)


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Walanae still have to be taking in to account, regarding earthquakes and tsunamis.

The Palu-Koro fault, which is also transform fault, contains two sub-fault;

A and B. Palu-Koro A goes from the center of the island straight to the west (to

Kalimantan) and divides Kutai Basin into two part. Palu-Koro B goes from the

center of the island up to the north and divides Palu. Meanwhile, the Matano A

goes from the edge of Southeast Arm until it reaches the center of Sulawesi. Littleto the south, there is Matano B, which also known as the Hamilton fault, goes to

the same point as Matano A. These two sets of faults combined with the North

Sulawesi Subduction Zone and spreading center at North Makassar Basin, have

also generated several earthquakes which had produced several tsunamis.

At the upper east part of Sulawesi, there is the Balantak fault, with several

subduction zones. It goes west from Halmahera Arc and Sorong fault, and then

after reaching the end of East Arm, goes straight up to the North Arm and parallel

with the Palu-Koro B (Guntoro, 1999, and Prasetya et al, 2001).

There are also several small faults, such as Batui, Sula, Ampana and Toli;

and trenches such as Sangihe and Tolo. Meanwhile the boundary of each

geological block of Sulawesi, especially the boundary of South (1) and Center (2)

is rapidly making movements; with the highest values occurred on the Gulf of

Bone and the Gulf of Gorontalo (Fig. 3).

Earthquakes and Tsunami in Sulawesi

All the big plates that surrounds Indonesia such as Indo-Australian,

Pacific, Caroline and Eurasia, are connected and attached to all of the 7 faults onSulawesi that mentioned earlier. This condition makes Sulawesi very vulnerable

of rapidly quakes, even though probably it would not produce a strong one.

From Global CMT, there are records of 270 earthquakes that occurred and

produced from these 7 faults during July 1976 to October 2009, with magnitude

more than 5.0.

Figure 4 shows that during all three periods from 1976 to 2009, it almost

has a linier trend of increasing total of occurrences. From the 1st

period (1976-

1987) increased 100% in the 2nd

period (1988-1998), and increased again to

almost 64% in the 3rd period (1999-2009). But in terms of the epicenter location,

which divided into land and sea, the trends are not being linier. The data showed

that the percentage of sea epicenter was increased almost 28% until late 2nd

period, but decreased about 9.45% at the end of 3rd

period. For the land epicenter,

it has the same pattern, but in the opposite value.


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Fig. 4. Trend of number of earthquakes occurrences during 1976-2009

These data give two possibilities of reoccurrence trend. First, in the next

period, 2010-2020, the number of seismic activity will tend to increase almost26.1%. Secondly, there is 50% chances that total number of sea epicenter will

become higher again, since the last period tend to go down. This assumption has

to be proven in detail at future research, since there are not enough data to use at

this present time.

Seismic prone areas are also founded from the Global CMT data. The author

classified seismic prone areas into three big areas (Fig. 5). They are:

1. Region A; bounded from North Sulawesi trench in the north and the EastArm in the south. It showed that the northern sea of North Arm, which

also called Celebes Sea, was the most active area. This area had a

subduction zone, where small plates being pushed below the Eurasian

Plate by Philippines, Caroline, Bismarck and Indo-Australia Plate, making

the North Sulawesi Trench. Below the North Arm, there is the Gulf of

Gorontalo, which contains the Una-una archipelago. These two areas,


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Fig. 5. Sulawesi Seismic Prone Areas Fig. 6. Sulawesi Seismic Gaps

produced almost 60% of the total earthquakes occurred during all the three

periods. All of these earthquakes are produced by Palu-Koro fault, North

Sulawesi Trench, Balantak fault, Sangihe trench and several other small

faults near the area.

2. Region B; bounded from East Arm in the north to the Southeastern Arm.Earthquakes on this area were influenced from several faults, i.e. Balantakfault, Sorong fault, Sula trust, South Sula-Sorong trust, Matano (A & B)

fault and Tolo trench. This region produced second largest amount of

earthquakes during the three periods.

3. Region C; bounded from the edge of the east side of Southeastern Arm upto Palu and covered all West Sulawesi and South Sulawesi Province.

Earthquakes at this area were influenced by the Paternoster, Walanae,

Matano B and Palu-Koro A. Even though this region had produced small

amounts of earthquakes comparing the two previous regions, but

unfortunately records three of tsunami events.

Based on these seismic prone areas, it will also show the seismic gap of the

entire area. Seismic gap is an area within a known active earthquake region or

zone which no significant earthquakes have been recorded. Figure 6 shows three

of the possible seismic gap, SG. They are:

1. SG A, positioning at the East Coast of North Arm. This area did not haveany record of earthquakes even though it situated just right at the Sangihe

Trench.

2. SG B; positioning at the West Coast of South Arm. This area did not haveany record of earthquakes even though it bound between Paternoster fault


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and Palu-Koro B fault and also strongly affected by the two spreading

centers in the North Makassar Basin.

3. SG C; positioning at the West, South and and East Coast of the southernpart of the South Arm. This area also did not have any record of

earthquakes even though it situated just right at Walanae fault and the

spreading center at blocks boundary of (1) and (2).

These three areas are well known to be potential area of seaquakes. There are

also evidence that even though the area had just strike-slip faults, still capable to

generate enough magnitude to produce tsunami.

Since its complexity, a special attention has to be conduct in Region A. Table

1 shows the average focal depth of the quakes, magnitude, and number of

occurrences in two part of sea in Region A. The first part is the Celebes Sea and

the second one is the Gulf of Gorontalo. At the first part, even though in the third

period (2001-2009) the number of event due to total occurrences in the relevant

periods and their magnitudes tend to go down comparing to other periods, the

Celebes Sea still having a high potential of strong quakes due to south and

southeast movement of Eurasian plate at the subduction zone on North Sulawesi

trench. At the second part, there is significant increasing on the number of event

due to the occurrences in the relevant periods, even though magnitudes tend to go

down slowly. But because of a lot of faults affecting the area from several

directions, as the first part, there is also a big potential of strong quakes can be

produce in this area.

Table. 1. Tsunami generated by earthquakes in Sulawesi

# Location DateEpicenter Depth

(km)Magnitude

Max Run

Up (m)Lat. Lon.

1 Makassar Strait 12/1/1927 -0.75 119.7 NA 6.3 15 (app)

2 Makassar Strait 4/11/1967 -3.3 119.4 20 6.3 8 (app)

3 Celebes Sea 8/14/1968 0.7 119.8 25 7.4 10

4 Makassar Strait 2/23/1969 -3.1 118.5 13 6.1 10

5 Makassar Strait 1/8/1984 -2.77 118.72 14.8 6.7 NA6 Celebes Sea 1/1/1996 0.74 119.93 15 7.9 3.4

7 Peleng Island 5/4/2000 -1.29 123.59 18.6 7.5 6


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During the last four hundred years (1692-2000), Sulawesi had been struck

24 times by tsunami (Latief et al, 2000, and Lander et al, 2003). Unfortunately,

not all of these data has been proven and connected with historical data of

earthquakes that generated them. From those 24 data, there were only 7 data of

tsunami impact can be retrieve and truly connected with the earthquake events asshown in Table 2.

These 7 events had several strong connection to each other, they are:

All were generated by shallow earthquakes, the focal depths (verticaldistance from hypocenter to epicenter) not more than 25km. Even though

the 1927 event did not have any record of depth, most of the experts said

that it definitely a shallow one.

Moment magnitudes of the quakes were moderate to large with magnitudeof 6.1 to 7.9. The magnitudes level was based on Scawthorn (2003)

categorization.

The entire epicenters were very close to the shore line; it measured notmore than 50km.

But besides those strong connections, these 7 events also contain several unusual

facts, they are:

Three of them were situated on the center of Makassar Strait, which is alsoon the lowest seismic prone area (Region C). They are 1967, 1969 and

1984 event. All of them were generated by shallow quakes produced byPaternoster fault and spreading center at the Makassar Basin, with depth

below 20km.

Only two of them were on the Region A, which is the highest seismicprone area. All happens in 1968 and 1996 event. All of them are also

Table. 2. Numbers and location of tsunami generated by earthquakes in Sulawesi

every 33years

Period events Locations

1910-1942 1 Makassar Strait (1927)

1943-1975 3 Two at Makassar Strait (1967,1969) and one at Celebes Sea(1968)

1976-2009 3One at Makassar Strait (1984), one at Celebes Sea (1996) and

one at Peleng Strait (2000)


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generated by shallow quakes produced by Palu-Koro fault and North

Sulawesi trench, with depth below 25km.

Peleng Island event on 2000 was the only tsunami event that occurred inRegion B, which is the second high seismic prone area. It was generated

by shallow quakes produced by Balantak fault and Sorong fault, with

depth of approximately 18.6km. Six of them were occurred in the West Coast, four in Makassar Strait and

only one in East Coast, near Peleng Strait.

Based on those facts, it shows the trend of movement of tsunami areas; from

the West Coast to the East Coast of Sulawesi. Also producers of the quakes that

can generate tsunami tend to move from Walanae-Paternoster fault to Palu-Koro-

Matano fault, Balantak fault and all other faults in eastern part.

Simulation of newest Tsunami in Sulawesi

To find out the approximate effected area and time of impact, simulation

of selected tsunami event have to be carry out. The events have to be the

representation of the three seismic prone areas. Based on that reason and

completeness of seismic parametric data, the three event chosen are the 1984

event for Region C, the 1996 event for Region A and the 2000 event for Region B

(Fig. 7).

The simulations were done by SiTPros v.1.2 (Chui-Aree, 2007), with basic

grid data from ETOPO2 and seismic parameter data from Global CMT.

The simulation of 1984 event

The main shock with magnitude of 6.7 was

occurred on January 8th

1984, 15.24 at local time on

2.77S 118.72E at the west coast of Mamuju

district, West Sulawesi Province (use to be South

Sulawesi Province). The fault dimension was 59km

in length and 34km in width. The epicenter was

4.32km from the closest beach.

Simulation results showed that first wave

will hit the closest beach less than 2minutes after

main shock, continued by the second one 2minutes

later. In 20minutes it will reached around 192km

Figure 7. Site of simulation.


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shoreline length of the west coast. In 40minutes, around 300km and after an hour

it reached around 393km (Fig. 8.a). This simulation showed that the 1984 event

took place in very shallow water because of the period was very short with quit

high celerity. It also showed a long shoreline effect, even though the run up tend

not to be so high.

The simulation of 1996 event

The main shock with magnitude of 7.9 was occurred on January 1st

1996,

at approximately 16.05 hours in the place with bearing 0.74N 119.93E at the

west coast of Toli-Toli district, Central Sulawesi. The fault dimension was 65km

in length and 26km in width. The epicenter was 10.2km from the closest beach.

Simulation occurs 6.2 minutes after the first and main shocking wave struck the

closest beach around, followed by the second one after 8 minutes later. At about

20 minutes time it reaches the 273km shoreline length of the west coast. In just 40

minutes, around 450 km and after an hour it reaches Gorontalos coast at north

east and almost reached West Sulawesis coast (Fig. 8.b).

This simulation showed that this event was typically happened in the

vicinity near to the field, even a local tsunami, which tends to reach the beaches

less than 30 minutes after the main shock. It was reported that the run ups reached

maximum around 3.4m at Tonggolobibi which is situated about 12.1km south of

the epicenter (Pelinovsky et al, 1997).

The simulation of 2000 eventThe main shock with magnitude of 7.5 was occurred on the 4

thof May

2000, at about 4.21in a place with corresponding bearing of 1.105S 123.05E at

the Peleng Strait of Luwuk Banggai district, Central Sulawesi. The fault

dimension was 71km in length and 35.5km in width. The epicenter was 7.5km

from the closest beach.

Simulation results showed that first wave hits the closest beach less than

2minutes after the main shock, another one followed after a minute later and

several more just a few minutes. Because of the epicenter was situated in the

Peleng Strait, the waves did not go out from that archipelagic area (Fig. 8.c). This

makes the run ups reached the maximum of 6 meters in Luwuk coastal areas and

devastated several coastal beaches of Peleng Island (Lander et al, 2003). This

simulation showed that this event was typically a local tsunami trapped on small

area which was generated by earthquake within that small strait. Unfortunately,

this situation tends to make the run ups higher.


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Fig. 8. Simulation results of (a) 1984 event, (b) 1996 event, (c) 2000 event

Based on these simulations, the three events definitely point out the same

results. First, all of these were called local tsunami. Second, since they generated

near or at coastal areas, there were very short time (less than 10min) from

generation until it reached the shoreline. And thirdly, the possibility of

implementing a local or regional early warning system at Sulawesi Island is

definitely reduced, making the possibility of using coastal fortress increased.


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Coastal vegetation in Sulawesi

Because of its long shorelines and position to the open sea, Sulawesi has

three major beach types, sandy, rocky and muddy beaches. The portion of West

(Makassar Strait) and North coast (Celebes Sea) are typically sandy and rocky

beaches; at the Gulf of Bone and Gulf of Gorontalo are muddy and sandy, while

the others are mostly sandy.Coastal vegetation in Sulawesi beaches also differs due to its habitats for

example, at sandy beaches there are Coconut (Cocos nucifera), Kembang Sepatu

(Hibiscus tiliaceus) and Screwpine (Pandanus sp); or for muddy beaches there are

Nipah ( Nypa fruticans) and several types of Mangroves, like Rhizophora

apiculata, Sonneratia alba andAvicennia marina (Nurkin, 1994). All of them can

be found at all Sulawesi coastal areas,

even in several rocky beaches, like on

Bira beach at South coast.

Though there are still covered

beaches, several researches indicates

that their population are decreasing

rapidly due to the establishment of

water ponds by villagers. For example,

according to Nurkin (1994); ADB

(1993), Whitton et al (2002), the

mangroves were degraded until almost

75% from 1950 until 1990 by all meansof disappearance scheme in South

Sulawesi Province (Fig. 9). Same cases

happened in other province, even

though their degradation is not as much

as in South Sulawesi Province. Due to

that problem, the government and

several community-based organizations,

from almost three decades are trying to

rehabilitate the loosing areas through

reforestation; but did not always

succeed (ADB, 1993). It also mentions

that there was small percentage of

coastal forest which width exceeds more than 200m located at Sulawesi Island.

Figure 9. Mangrove distribution map of South

Sulawesi Province.


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RESULTS

Based on previous explanation, the analysis was done by making an

integrated plot of advantages and disadvantages of each part of materials, i.e.

earthquakes data, tsunami data and vegetation data.

From earthquakes and other geological data, we found out:

1. Moderate to large earthquakes (Mw>5.0) in Sulawesi were tending to shiftto east part of the island due to actively spreading centers in MakassarStrait, Paternoster and Palu-Koro fault. For all that matters, the potential

area that reasonable for quakes were Celebes Sea, Gulf of Gorontalo, Gulf

of Bone, Banggai archipelago, Sangihe, Matano and Sula archipelago;

which automatically made the associated beaches as tsunami prone areas.

2. Geological marks that can eventually be the epicenters were the NorthSulawesi trench, Sangihe trench, Tolo trench, Balantak fault, Matano fault,

Sorong fault, South Sula-Sorong fault, Batui trust, Sula trust and several

small faults at Center Sulawesi Province.

From tsunami, we found out:

1. All tsunami in Sulawesi Island were tending to be local with moderaterun-up high, between 0.1m until 6m.

2. Due to its generating area and beach morphology, all the tsunami inSulawesi Island could reach nearest beach below 10 minutes after the

main shock and rapidly impacting in two or three successive waves.

3. The impacting shoreline could cover as much as it could be, below an houror so; making the large possibility of affecting area at beaches.

From coastal vegetation, we found out:

1. There were several coastal plants that can be found all in West and Eastcoast of Sulawesi Island. They were Coconut (Cocos nucifera), Kembang

Sepatu ( Hibiscus tiliaceus), Screwpine (Pandanus sp), Nipah (Nypa

fruticans) and several types of Mangroves, like Rhizophora apiculata,

Sonneratia alba andAvicennia marina.

2. There were degradation of those coastal plants, especially Mangroves dueto the opening of water pond (for fishing and desalinitation) and

cultivation made by the villagers.

3. Reforestation of mangroves and other coastal plant are still ongoing, eventhough sometimes ends with no forest at all.

The next step is finding the intersection between three of them, beginning on

earthquake and tsunami, which were:


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Fig. 10. Relationship between earthquakes,

tsunami and coastal forest as tools for

possibility analysis

(a) With relatively small covered reducedimpact area, poor research and

reforestation scheme

(b) With reduced impact area covered allimpact area, generated by earthquake-tsunami

(c) With reduced impact area covered allimpact area, generated not only by

earthquake-tsunami But also other

causes, such as landslides and volcanic

eruption

Characteristics of earthquakes which could generated tsunami, basic onrecords, were:

o Focal depth less than 20kmo Mw > 6.0o Epicenter near the shore line

Corresponding movement at trenches, subduction zones, transform faultsand spreading center. But most of all, subduction zones and trenches,which narrowed to Celebes Sea, Gulf of Gorontalo, Sangihe trench,

Banggai archipelago and Gulf of Gorontalo

Characteristics of tsunamigenerated, basic on records, were:

o Local tsunami; time impactshorter than 10 minutes after

main shock

o Maximum run up height notexceed 6 meter

o Successive until threewaves, making it much more

constant in run up height

The intersection between tsunami and

coastal vegetation, which were:

Area that have to be supported withcoastal vegetation were:

o North and South coast of theNorth Arm (Gorontalo

Province and North

Sulawesi Province)

o North and South coast ofCenter Sulawesi Province,

including Una-una and

Banggai archipelagoo East coast of South arm

(South Sulawesi Profince)

A coastal vegetation structure wasbased on dominant crown zones,

for example at mangrove forest


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beginning from zone Avicennia-Sonneratia, Rhizophora-Sonneratia and

lastRhizophora-Bruguiera. Not only with mangroves class, but also above

mean tidal zone; until it reaches trees, such as Coconut.

Width of each zone was based on physical experiments results; whichbeginning to be effective from 200m until 400m (Harada and Imamura,

2005).

DISCUSSION

Interpretation of all the result was done by combining these two kinds of

intersections and founded by using simple geometrical function of equilateral

triangle; of earthquake, tsunami and coastal forest (Fig. 10). If all research

corresponding to the tsunami-mangrove dynamic interaction result can be

implemented with full force and directly goes to implementation of reforestation

of coastal vegetation, then the capability of reducing the impact will depend on

the value of L, as side length of the equilateral triangle of the intersection.

The implementation of natural coastal forest as fortress is depend on the

force that pushed the triangle of coastal forest to its proper position which will

cover all the intersection of earthquake and tsunami, but with OA line as fixed

plane.

= 1

2. .

3

2.,

with ACF as area of Coastal Forest Triangle and L as length side of the

equilateral triangle.The increasing value of L at Coastal Forest Triangle will make the

intersection of reduced impact area become bigger and beginning to cover the

intersection of Earthquake Triangle and Tsunami Triangle which represent the

non reduced impact area. Furthermore, if this can still be improved, the Coastal

Forest Triangle will cover all the Tsunami Triangle and even become bigger. This

means, all of the tsunami area will be reducing, not only that generated by

earthquakes but also other causes, such as landslides or volcanic eruption. If it

directly connected with the actual area and based on limitation of the effective

width of coastal forest suggested in some previous research, the value ofL willautomatically correspond to the length of shore line. In the case of Sulawesi

Island, there is still a small percentage of coastal forest with the width minimum

purposed by Harada and Imamura (2005). It means that there is a possibility of

implementing natural coastal forest as fortresses from tsunami impact, based on


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the existing forest; but will not cover all the tsunami prone areas mention earlier,

without any exerting extra efforts.

Due to this condition, future researches had to be conducted to find out the

relation between dimensions of the actual Coastal Forest Area in the selected

tsunami prone areas. Research regarding of finding the possible schemes of

coastal vegetation structure to increase the dissipated wave energy when itinundated the coastal zone, will also be helpful.

ACKNOWLEDGEMENT

The authors are indebted to anonymous reviewers and for Dr Hamzah

Latief of his 400years tsunami data.

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