T S U N a M I S T S U N a M I S Thucydides Was a Greek Philosopher Who Was Nami Waves Can Cause Severe Damage

No. 16, August 2011 WASPADA News On Earth Disasters

Contents T S U N A M I S T S U N A M I S Thucydides was a Greek philosopher who was nami waves can cause severe damage. known as the “father of science”. Whatever he Tsunamis wave can be triggered by verti- said was always accompanied by a scientific cal changes in sea floor that move a large analysis rather than the common culture of the amounts of water. Most of tsunami events Greek people, associating everything to the power were generated by an earthquake that oc- of the Greek Gods. One of his famous stories is curred in the seafloor, when the large amount “a history of the war of the Peloponnese.” In this of water was driven by the increasing or a Publisher book, Thucydides recorded the natural pheno- decreasing of hundreds or even thousands PT. Asuransi MAIPARK Indonesia mena which destroyed the Bay City of Maliakos square kilometers of seabed. Landslides and Euboic. It was the huge sea wave in the sum- (which often follow the large earthquakes), Advisor mer of 426 BC. He concluded that the destructive volcanic eruptions in the sea, and the mete- Frans Y. Sahusilawane wave must be generated by something else, and it ors can also disrupt the balance of water to Bisma Subrata was an earthquake at the bottom of the sea. generate the tsunamis. Now, the huge wave is called the ‘tsunami’, de- The tsunami wave can travel thousands ki- Editorial Board Mudaham T. Zen rived from the Japanese vocabulary which is li- lometers across the ocean without losing Andriansyah terally means harbor wave, referring to the disas- its energy. For example, the tsunami that Fiza Wira Atmaja ters that often occur in the port cities in Japan. In occurred in 1920 in Chile, South America, Ruben Damanik addition to the earthquakes, such as hyphothised caused a serious damage in Japan, 14.500 M. Haikal Sedayo by Thucydides, a tsunami can also originate from kilometers (9.000 miles) far away. Hawaii, Hengki Eko Putra underwater landslides, volcanic eruptions in the in the middle of Pacific Ocean, is very vul- Bintoro Wisnu ocean, or a meteor falling in the ocean. These nerable to the tsunamis because it’s located Jyesta Amaranggana events can make the vertical displacement of the in the middle of ‘tsunamis traffic’. seafloor just in the blinking of an eye,- thisbe The tsunami was preceded by an earthquake Editorial Address comes the starting point of the tsunami theory. at the bottom of the sea, where the seabed Corporate Secretary The tsunami wave can propagate in all directions. oscillates up and down due to pressure from PT. Asuransi MAIPARK Indonesia Setiabudi Atrium Building, 4th The large energy is contained in the height and below (the earthquake). Vertical movements Floor, Suite 408 speed of the waves. In deep oceans, these waves of the Earth’s crust can be very large and lift Jl. HR. Rasuna Said Kav. 62, propagate at the speed of 500-1000 km per hour the sea water above the normal sea level. Jakarta 12920 with the height only about 1 meter. This configu- Thus, the main factor of the tsunami is a ver- ration changes as it approaches the coast, the tical deformation of the seabed. The height Tel.: (021) 521 0803 speed of tsunami wave decreases to 30 km/hour, of water above sea level is encouraged into Fax : (021) 521 0738 but its height increases until ten meters instead. potential energy. Then, the potential energy E-mail: [email protected] is transferred into kinetic energy, which di- Website: www.maipark.com The Mechanics of Tsunami Forma- rectly affects the speed of tsunami wave. tion When the tsunami took place, the speed of At one time, the tsunami regarded as a tidal wave, tsunami wave does not only depend on the but because the tsunamis are not caused by the kinetic energy of the earthquakes, but also gravitational force of the Moon and the Sun, from the surrounding conditions. The speed hence the ‘tidal wave’ term is no longer used. of the tsunami is varied, which is directly Tsunami is a height wave that is usually created correlated with the depth of the ocean, in by the large-scale movement of the seafloor. Al- the deep ocean tsunami wave move faster. though the ‘body of tsunami’ is barely visible in At some points in the Pacific Ocean, which the sea, but when it reaches the shoreline, the tsu- are reaching 4000 meters depth, the tsunami waves can travel more than 700 km/h, with wavelengths greater than 100 km. In contrast to the tsunami caused by the earthquake, the tsunami from landslides and volcanic eruptions in the ocean quickly disappears and rarely affect the beach which is located far from the source. However, this kind of tsunami still has the same destructive force: in 1883, the tsunami caused by the eruption of Krakatoa killed more than 36.000 people on nearby islands of Java and Sumatra. Tsunami-genic earthquake An earthquake is the release of energy in the earth which occurs very suddenly. The shallower the earthquake, the bigger opportunity for the faulting to change the surface morphology. If the focus of the earthquake is deep, the faulting can be classified as blind faults, it means the faulting only occurs below the surface and does not reach the upper surface. Figure 1 Vertical movements of the Earth’s crust lift the sea water above the So, in order to generate a tsunami, the earthquake must: (1) normal sea level (Photo: http://www.clinicalcorrelations.org) be centered at the bottom of the sea, (2) has a shallow focus, and (3) has significant vertical throw (indicated by the amount of energy that is released). Statistically, the earthquake that causes tsunami is the earthquake that centered in the ocean with the depth < 45 km with a magnitude > 6.5 Mw (Satyana, 2007). Figure 3. shows the Indonesian earthquake source zones. The red line indicates the subduction and thrusting zone, which has vertical faulting characteristics. The orange line indicates the strike slip faults, with horizontal faulting characteristics. So, the subduction and thrusting zone in the ocean can generate the tsunami-genic earthquakes.

Figure 2 Sketch of shallow and deep earthquake

The Earthquake history in Indonesia: the first and largest The record of Indonesia tsunami has started in 1608, when Mount Gamalama in Ternate Island erupted and caused a tsunami which killed 10-50 people. Since then, there were 227 tsunami events recorded all over Indonesia. 23 of them were caused by volcanic eruptions, just like the Gamalama’s tsunami, and 204 other events were caused by the earthquakes. So far, Aceh tsunami in 2004 was recorded as the most deadly tsunami in Indonesia. It is estimated that more than 230 thousand people were killed in this event. The majority of the victims, 167.736 people, are residents of the Province of Nanggroe Aceh Darus- salam, Indonesia, followed by Sri Lanka (35.322 people), India (18.045) and Thailand (8.212). The tsunami wave traveled more than 5,000 km to the west coast of Africa and has killed several people in Kenya and South Africa. Yes, the Aceh tsunami was the most deadly tsunami in Indonesia, but it was certainly not the biggest one. The height of Aceh tsunami waves reached about 10 meters, which is still low if compared to the height of the waves from the Krakatoa eruption in 1883, which was reported to reach 40 meters. The Krakatoa’s tsunami killed 36.000 people in west coast of Banten and in the south coast of Lampung Province. The body of Mount Krakatoa that collapsed into the sea caused a huge tsunami waves which reach Anyer just in one hour, and hit Jakarta Bay in 2.5 hour after the eruption. Figure 3: Indonesian Earthquake source zone map. The subduction and thrust indicated by the red lines. The position of the earthquake source zone in the ocean increases the possibility of tsunamis, every time it releases energy. The last two decades of Earthquake History Tabel 1. Eight most deadly tsunamis in Indonesia in Indonesia Only within two decades, there were 25 tsunami events in Indo- nesia. It’s not surprising due to the condition of subduction and thrusting zone that extends in most parts of Indonesia, from the West Coast of Aceh to the South Coast of East Java and in the eastern part of Indonesia and Sulawesi. The large earthquakes (>7) which followed by tsunamis are: Banyuwangi 1994 (Mw 7.8), Aceh, 2004 (Mw 9.3), Nias 2005 (Mw 8.6), Pangandaran 2006 (Mw 7.7), Bengkulu 2007 (Mw 7.8), Padang 2009 (Mw 7.8), Tasikmalaya 2009 (Mw 7.3), and the recent one is the Mentawai tsunami in October 2010 (Mw 7.7). Many scientist claims that this area has not released all of its energy yet. The three main areas are: (1) the area around the Siberut Island, (2) Sunda Strait region, and (3) the South Coast of Java, from Cilacap until Pacitan. So, preparing for the worst scenario, we can assume that the Mentawai’s tsunami might not be the last big tsunamis during these two decades. During the last two decades in Eastern Indonesia, tsunamis hit Flores in 1992 (Mw 7.8), Halmahera, 1994 (Mw 7.0), Timor Sea 1994 (Mw 6.5), Biak 1996 (Mw 8.2), West Papua, 2002 (Mw 7.7), Alor Islands 2004 (Mw 7.5) and Seram island, 2004 and 2006 (6.7 Mw, Mw 6.7). Official agencies record that the Flores tsunami killed 1.169 Figure 4: The colored polygons indicate the faulting areas in each earthquake event. Siberut Island, Sunda Strait region and the south coast of people, whereas the mass media reported that the number of Java identified as the un-released energy zone. (The map from US. Geologi- victims reach 2.500 people. This is the biggest deadly tsunami cal Survey) in eastern Indonesia. The tsunami waves arrived 5 minutes after the earthquake. The local people reported that the wave arrived at least 3 times and the second wave was the highest. The Flores tsunami derived from the earthquake in the Flo- res Thrust, which stretchs from Flores to Bali Sea. The Flores thrust activity in north of Nusa Tenggara Island to Bali can be a serious threat. History records that the earthquakes and tsunamis occurred in 1815, 1817, 1857 and 1917.

Figure 5: The map of Bali, Nusa Tenggara and Timor Island. The Flores thrust (red line) in the north of these islands is the source of earthquakes and tsunamis in Flores 1992. (The topographic map from NOAA) Insurance perspective Tabel 2: The catalogue of tsunami events in Indonesia during the last two decades. The comparison between insurance losses and economic losses in the two Year Month Date M Area Latitude Longitude Victim recent incidents of earthquake-tsunami disaster are very small, it shows that 1992 12 12 7.8 FLORES SEA -‐8.480 121.896 1.169 insurance penetration is very low. 1994 1 21 7 HALMAHERA 1.015 127.733 Whereas, 78% of the loss is personal and residential property which is the 1994 6 2 7.8 JAVA, INDONESIA -‐10.477 112.835 250 target of disaster insurance market. Overview of disasters loss data in In- 1994 6 3 6.6 JAVA, INDONESIA -‐10.362 112.892 donesia showed that the national insurance industry has not been well 1994 6 4 6.5 TIMOR SEA -‐10.777 113.366 contributed in the risk management of the earthquake and tsunami disasters. 1994 10 8 6.8 HALMAHERA -‐1.258 127.980 1 Insurance penetration is the major pro- blem that needs to be solved as soon as 1995 5 14 6.9 TIMOR SEA -‐8.378 125.127 11 possible. The mitigation programs that 1996 1 1 7.9 SULAWESI 0.729 119.931 9 increase the people’s knowledge and awareness to the risk need to be done 1996 2 17 8.2 IRIAN JAYA -‐0.891 136.952 110 on the insurance industry. On the other hand, the Government should play a 1998 11 29 7.7 TALIABU ISLAND -‐2.071 124.891 proactive role to encourage people to insure their property. Indonesian go- 2000 5 4 7.6 SULAWESI -‐1.105 123.573 vernment could follow the Japans insurance scheme that adds an insurance 2002 10 10 7.6 IRIAN JAYA -‐1.757 134.297 premium on tax bill. 2004 1 28 6.7 SERAM ISLAND -‐3.120 127.400

2004 11 11 7.5 KEPULAUAN ALOR -‐8.152 124.868 Paleotsunamis The tsunami waves arrive with the 2004 12 26 9.3 SUMATRA 3.295 95.982 227.898 speed just like a jet plane, transport 2005 3 28 8.7 NIAS 2.085 97.108 10 material in the form of sand, plants, even biotas from the deep-sea, and de- 2005 4 10 6.7 KEPULAUAN MENTAWAI -‐1.644 99.607 positing them in the beach area. On the beach, tsunamis wipe out everything 2006 3 14 6.7 SERAM ISLAND -‐3.595 127.214 4 on its path, and inundating the coastal areas. 2006 7 17 7.7 JAVA -‐9.254 107.411 690 Based on these characteristics, scien- tists can track tsunami events in the 2007 9 12 8.4 SUMATRA -‐4.438 101.367 past, when there is no record about the 2008 2 25 6.5 SUMATRA -‐2.486 99.972 parameters of the tsunamis and earthquakes from seismographs. Through 2008 11 16 7.3 SULAWESI 1.271 122.091 the tsunami’s traces left in the coastal area, the geologists can estimate when and how big the tsunami is. Paleotsu- nami is the name of the branch of geo- logy that focuses on this study. Gene- rally, the traces of past tsunamis have remained in the coastal area in the form of deposits material that brought and dumped a shore during the event. From the information of Newcomb and McCan (1987), it is known that the earthquakes which followed by tsunamis happened three times: in 1840 and 1859 that hit Bantul, Gunungkidul, Wonogiri and Pacitan, and in 1921 that swept Pangandaran, Cilacap, Kebu- men, Purworejo, Bantul and Gunung Kidul (Figure 6) . Unfortunately, there are no further detailed information about the earthquake source parameters. Figure6: Three tsunami record data in the south coast of Java. Tsunami in Pangandaran 1921, likely has repeated by the tsunami in last 2007. While Bantul, Gunung Kidul, Wonogiri and Pacitan never hit by the tsunamis as they were happened in 1840 and 1859 (The figures and notes of the tsunami are taken from Newcomb and McCan, 1987)

In order to analyize the raw data from Newcomb and Mc- Can, the Research and Development team of PT. Asuransi MAIPARK Indonesia conducted a paleotsunami study in Wonosari and Pacitan. The main target of this survey is to estimate the wave height and coverage from the tsunami that occurred nearly a century ago. In addition, by studying the morphology of the areas through satellite images and ground observation, the survey team dis- cussed the disaster mitigation in the areas concerned. These tsunamis which occurred nearly a century ago, could happen again in the future. So the concrete actions from the government institutions in tsunami mitigation has to be done right away and be planned as accurate as possible. From field observations, the team has found the layers of sand Figure 7: The Satellite image of the south coast of Wonosari. The red stars which are assumed to come from the tsunami that occurred a are the points where MAIPARKs team held the Paleotsunami excavation; Krakal hundred years ago. On Sepanjang Beach and Baron Beach, Beach (KRK 01 and 02), Baron Beach (BRN 01) and Sepanjang Beach (SPJ 01 and 02). (This Satellite image is from Google Earth, 2010). the team found a layer that indicates one tsunami event. The layer was found at a depth of 1.8 m (Sepanjang Beach) and 1.7 m (Baron Beach). Meanwhile, in Pacitan, the survey team found the layers of tsunami deposit at a depth of 0.6 m.

South Coast of Java The seismicity levels in the South Coast of Java are domi- nated by the subduction activities of Indian Ocean - Australia plate that subducted to the Eurasian plate. The subduction earthquakes that followed by the tsunami in the last 2 decades are Banyuwangi Earthquake (1994) and Pangandaran Earthquake (2006). Banyuwangi tsunami occurred in June 3, 1994, the earthquake epicenter was about 200 km from the nearest coastline, to the Indian Ocean. The tsunami caused serious damage and numerous victims in the coastal areas. Desa Rajekwesi, Pan- Figure 8: Pacitan Bay. Pacitan city, located in the coastal area, is very vulnerable to the tsunami waves. MAIPARKs team held the Paleotsunami excava- cer and Lampón, Banyuwangi suffered the greatest damage. tion on PCT 01, 600 meters from coast line. ). (This Satellite image is from The tsunami wave also reached Desa Soka, Tabanan, Bali. the Google Earth, 2010). There were no fatalities in this village, but the run-up off the quake. Reportedly, the area around Pangandaran is the most deva- tsunami waves reached 5 meters from the coastline washed stated by the 3 metres tsunami waves. In Cilacap, at least 157 people several fishing boats. dead and 104 missing, while in Kebumen, 10 died and 33 missing. In An Mw 7.7 earthquake in the Indian Ocean triggered a tsuna- Yogyakarta, six people were confirmed dead - two victims in Drini mi that arrived on the coast line about an hour after the earth- Beach, Gunung Kidul and one person in Parangtritis, Bantul. Image from Ikonos satellite shows the impact of the tsunami in Pangandaran Beach in July 19, 2006. The most dramatic evidence in this picture is the border of tsunami’s run up which showed fragments of building materials, most likely from the building in coastline that devastated by tsunami waves.

Seismic Gap In the last two decades, western and eastern part of south coast of Java was have been hit by the tsunami waves. The middle part of south coast of Java also had the same potential to be af- fected by the tsunami. The history of earthquakes in the South coast of Java from Newcomb and McCan’s note indicate that this area was last hit by the tsunami in 1840 and 1859. From the seismicity point of view, this area is in the process of accumulating seismic energy, indicated from the low b-value.

Tsunami Mitigation Figure 9: The deposit of tsunami at Sepanjang Beach. The irregular path of MAIPARK research found the indications of the tsunamis in the sand layer shows that the tsunami came up in a series of waves. The South Coast of Java, definitely, the tsunamis could happen thickness of the sand deposit reaches 30 cm.

Figure 11: The tsunami deposit at Baron Beach in 0.6 m depth. The thickness of the layer at Figure 10: The tsunami deposit at Baron Beach in 1.7 least 25 cm. m depth. The thickness of the layer is about 20 cm.

Figure 13: Housing and cottage on the coast in Rajak- Figure 12: Earthquakes in South of Java wesi that washed away by the tsunami (Photo: Maramai and Tinti, The 3 June 1994 Java Tsunami: A Post-Event Survey of the Coastal Effects) again in the future. But not all regions in the South coast of early warning system. This should not always be interpreted as to Java are highly tsunami prone, only some areas have a ‘trap’ be very modern system with sophisticated and automated system. If morphology which are considered dangerous when tsunamis we do not have a modern system, it can also be done through simple occur. The tsunami waves will hit this area and the population devices! Such as, a simple installation of observation towers along are trapped between the walls of limestone hills, if no mitiga- the coast, as practiced by European countries during World War II. tion program is conducted. The watcher focus to observe the behavior of coastal waves, and Therefore, the Government is urged to start the tsunami miti- when he sees the sign of the tsunami (a sudden receding of water gation program. The tsunami mitigation program must have an from the coastline for example) he must send the emergency sig- nal to the surrounding communities immediately. It also can be done with the simple equipment, like the kentongan bamboo. Every time the kentongan bamboo was alarmed, the people must run to the safer place. This technique has a weakness that can only be done in daytime, but it is much better than modern early warning system equipment which we don’t have. In the other hand, the morphology in some places has advantages. The limestone hills with the height up to 14 meters can be a safe place to escape when the tsunami wave came. But, these hills must be well facilitated, so in that time of emergency, people only need a few minutes to reach this place. The easy and safe evacuating routes must be prepared for everyone, even the elder, women and children. From satellite images observation, areas with hills of limestone often found in the eastern part of Java Island, extending from the Gunung Kidul to Banyuwangi. In contrast, from Parangtri- Figure 14: Damage caused by tsunami wave in Desa Lampon (Photo: Maramai and Tinti, The 3 June 1994 Java Tsunami: A Post-Event Survey of the Coastal tis to the western part of South Coast of Java, coastal areas tend Effects) to have flat morphology. Figure 18 is examples of the bay areas in the South Coast of Java that “advantaged” by the presence of limestone hills in the vicinity. This limestone hill could be a good place for evacuation in an emergency tsunami. To take those advantages, the tsunami drill or simulation must be held regularly and continuously, every 6 months for example. The residents should be prepared for emergencies, so they will not only understand the risk of tsunamis, but also be well trained when disaster occurs. So, the panic that occurs when the disaster came can be reduced. This role must be taken by the Local Disaster Management Agency (BPBD), in coordination and direction of the National Disaster Management Agency (BNPB). This is not an impossible thing to be done, but a ne- cessary thing to do in all those areas. MAIPARK take the initiative to conduct the tsunami drill.

Baron Beach at Kabupaten Gunung Kidul was chosen as a pi- Figure 15: Aerial view of Pangandaran beach after tsunami July 2006 (Photo: lot project area. Construction of tsunami evacuation route and http://earthobservatory.nasa.gov). counseling session to coastal people will precede the tsunami drill program. Local Disaster Management Agency, Public Work Agency and Tourism Agency along with government of Kabupaten Gunung Kidul will involve in the program. The program that will directly involving the community from all ages, including elementary school age, very expected to be a valuable “equipment” for the people to deal with the tsunami disaster.

Conclussion 1. Not all areas indicated in the ‘tsunami map’ of Java pu- blished by BNPB and BMKG are tsunami prone. In con- tradiction with the North coast, the South coast of Java in numerous place are naturally protected by limestone cliffs which consist of coral reefs, rise perpendicular from the Figure 16. Historical Earthquake reported in Newcomb and McCan (1987). 1840 sea, forming sea walls which at many places reach up to and 1859 earthquake is figured as tsunami-earthquake events. 30 meters from sea level. These regions are naturally protected againts tsunami events. 2. However, not the entire coastline is naturally protected, at some places there are inlets, bays with lowlands and pretty beaches. These beaches are frequented by vacationers during weekends and holidays. These beaches are not protected. There are no early warning system, no guard posts with guards to supervise the safety of the swimmers againts drowning or being swept away by rip currents into the ocean. Beaches in bays like this are numerous, like Pangandaran, Baron, Krakal, Kukup, Sundak and Pacitan. 3. If an earthquake happens in the seismic gap area mentioned Figure 17 The b-value map for subduction zone of Southern part of Java. Low before, these inlets will become death traps for vacationers value indicated by the blue color is expected to be an accumulating energy and for the local population who live there. zone. This “seismic gap” would likely to produce a big earthquake. Figure 18: The shape of ‘trap’ morphology. The tsunami waves will hit this area and trapped between the walls of limestone hills. Recommendations

Four things are needed to prevent a catastrophy to occur, these are : i. Local population and the vacationers must be ‘educated’ with respect to what tsunamis are, how to save oneself and where to run. ii. A training and drill program must be conducted regularly, to train the local population and vacationers. If they are not regularly trained, a panic will occur and could be worse than the tsunami itself. iii. The lowlands and beaches in the South Coast of Java are usually surrounded by limestone hills or bioherms, or limestone hills running parallel to the sides of the bays or inlets. They are quite steep. A path or stairs must be provided for women, children and elder people to go up to hills for safety. These path-ways must be ‘maintained’ constantly. iv. A traditional or simple early warning system must be set up like a wooden/bamboo watchout tower with a guard watching the sea continuously. a. A tsunami wave can usually be seen approaching the shore from kilometers away. b. Very often than not, one can see the water receding far from the shore before the waves come rolling back. Our local wisdom from Simeuleu Island in Sumatra teaches us: ‘Jika melihat laut sekonyong-konyong menyusut jauh dari bibir pantai, larilah ke tempat-tempat yang lebih tinggi!’ (if you see the sea suddenly receding far away from the shore, run to the higher ground). With traditional signals, the guard from the water post could alarm the people to run to safer ground, and still have time to save himself to higher grounds. Of course a traditional and simple system like that will not be effective at night. Considering that most vacationers, swimmers and surfers will be in the beach at day time, a device described can still be useful, compare to having nothing at all. However, setting up such a device needs the supervision from the Local Disaster Management Agency (BPBD) or any local authority coordinated by BNPB. Last but not least, those guards must be well paid, so that they will conduct their duty properly. The most difficult thing is the continuousness and persistent discipline. This is not a one day, week, or month activity, but for always, as long as Indonesia has beaches which are tsunami prone. Finally, a thorough survey along the South coast of Java and other islands have to be carried out by BNPB, LIPI, BPPT, universities, research institutions and by the NGO’s, so that Indonesia will have a more complete information of the shores and beaches. This will certainly take years, but with the aid of satellite images followed by ground truths observation on the spots, will shorten the time for the assessment of tsunami prone coast line.