EERI Special Earthquake Report — August 2005 Learning from Earthquakes The Northern Sumatra Earthquake of March 28, 2005 Editor’s Note: Beginning with the killed around 1,000 people while they occurred. Right after the earth- March issue and in each one sub- were either sleeping or trying to run quake, electric power was cut off sequently, we presented six reports from the second and third fl oors. In and telecommunication disrupted. by the many teams that observed Simeulue, some house shops col- In Gunung Sitoli and Teluk Dalam, the effects of the December 26, lapsed, and about 100 people were Nias, the damage was concentrated 2004, earthquake and tsunami in killed. There was a rush to exit in certain areas close to the beach. countries around the Indian Ocean. houses and run to higher places be- In Simeulue the damage was also This report adds information on cause the people feared a tsunami concentrated in areas close to the structural damage, largely from similar to that of December 26, 2004. beach. Strong aftershocks (32 km shaking, on two islands west of There was a local tsunami, but not from Gunung Sitoli [M 6.0] and 41 Sumatra in a subsequent large of the size or ferocity of the previous km from Sinabang (M 5.5]) did not earthquake in roughly the same one. cause any further damage to either epicentral area as the December damaged or undamaged buildings. quake. Publication of this report is Nias Island is part of North Sumatra supported by funds from the Na- Province and Simeulue Island is part tional Science Foundation through of Aceh Province. The population of Tectonic Effects EERI’s Learning from Earthquakes Nias is 730,000 and that of Simeulue During the survey in Simeulue as Program under grant # CMS- is 80,000. Most of the people on Nias well as in Nias Island, we observed 0131895. and Simeulue were already asleep, some subsidence in certain very or about to be, when the earthquake limited areas. There were also “pop- Within a few days of this earth- quake, a team set out from Jakarta to study the earthquake damage on the islands of Nias and Simeulue. The team leader and author of this report was Teddy Boen, consulting engineer in Jakarta and senior advi- sor, WSSI. Survey team members on Nias were Teddy Boen, G. Hen- dra, P. Idrus, K. John, James Wong, M. Agus, and B. Bernard. Survey team members on Simeulue were Figure 1. Teddy Boen, G. Hendra, and Akil R. Main shock and Karsono. aftershocks of the Nias/ Introduction Simeulue earthquake, On Monday night March 28, 2005 March 28, 2005 at 11:09 pm local time, the Nias and (USGS). Simeulue islands were shaken by a M8.7 earthquake with a depth of 30 km. The epicenter of the earth- quake was on the Great Sumatran fault, between the two islands at 2.074°N, 97.013°E (see Figure 1). This is 115 km from Gunung Sitoli, the district capital of Nias, and 84 km from Sinabang on Simeulue. In Gunung Sitoli and Teluk Dalam, many house shops collapsed and 1 EERI Special Earthquake Report — August 2005 Figure 2. “Pop up” beach at Matanurung, East Simeulue. Figure 3. Local tsunami height approximately 1.80 m. up” beaches in Nias and Simeulue, by the tsunami, and some buildings engineered buildings except for caused by uplift (see Figure 2). Staff collapsed. The local tsunami went district head offi ces, hospitals, and members of NGOs who worked in inland up to 400 m in Hiliamaetani- some other government buildings. several places across Simeulue re- ha. From the damage, it appeared Engineered buildings consist mostly ported that they also observed simi- that the fl ow force was not too of reinforced concrete combined lar pop-up beaches all over the is- strong. In Simuelue, traces of local with masonry walls. Almost 95% of land. tsunami could be seen in Labuan the buildings are nonengineered, Bajau primary school # 2 (see Fig- made of confi ned masonry half- After the earthquake, a local tsunami ure 4). The tsunami height was ap- burnt brick, concrete block, and hit limited areas. In Nias, along the proximately 0.5 m and no evidence timber. road entering Sorake and in Sorake of fl ow force could be seen. itself, the tsunami height was ap- Engineered Buildings: Some en- proximately 1.80 m, as can be seen Damage to Buildings gineered buildings in Nias and Sim- on the wall of house in Hiliamaetani- eulue were damaged during the ha, approximately 1 km from Sorake Two types of buildings were affect- earthquake, and some collapsed. (see Figure 3). In Sorake, several ed: engineered and nonengineered. There are two main reasons for this. building foundations were scoured In Nias and Simeulue, there are few The reinforced concrete buildings Figure 4. Damage by local tsunami in Labuan Bajau school, Simeulue. Figure 5. District head offi ce in Simeulue. 2 EERI Special Earthquake Report — August 2005 Figure 6. Damage to district head offi ce in Nias. Figure 7. Damage to district head offi ce in Simeulue. were not designed for the seismicity dance with requirements for earth- cement mortar; and 3) timber build- of the islands. We also found that quake-resistant construction (see ings. In some areas, sea sand is poor quality of concrete and detail- Figures 6 and 7). used for concrete mix and, of ing contributed to the collapses. course, results in poor quality Even though Indonesia has a seis- Nonengineered Buildings: Most of concrete. mic code, it was not enforced in the buildings were nonengineered either island. Additionally, the build- that collapsed in Gunung Sitoli in The one or two-story buildings were ing permit system was not yet in Nias, Sinabang City in Simeulue, mostly houses, schools, and com- place. and villages along the road from munity health centers. The roofs of Sinabang to Labuan Bajau and from the houses mostly consist of gal- For example, both district head’s Gunung Sitoli to Teluk Dalam in Nias. vanized iron sheets or thatch made offi ces were damaged (see Figure There are three main categories of of coconut tree leaves; other build- 5). We surmise that in each case, nonengineered buildings: 1) one or ings use galvanized iron sheets. the structure was analyzed as 2-D, two-story houses of burnt brick or These masonry buildings survived with the torsional effect overlooked. concrete block masonry with sand/ the shaking without collapse, From the damage, it was evident cement mortar; 2) two to four-story though some had cracks in the that the concrete quality was low shop houses of burnt brick or con- walls (see Figure 8). and the detailing was not in accor- crete block masonry with sand/ Figures 8a and b. Nonengineered masonry houses damaged and collapsed in Nias. 3 EERI Special Earthquake Report — August 2005 Figure 9. Timber houses collapsed in Nias due to lack of Figure 10. Traditional indigenous house in Nias, not maintenance. damaged. Figures 11a and b. Traditional indigenous houses damaged due to lack of maintenance in Bawogosali Village, Teluk Dalam, Nias. The two to four-story shop house buildings also use burnt bricks or concrete block masonry with sand and Portland cement mortar. The roofs of these shop houses are Figure 12. usually RC slabs. All the buildings Indigenous house use RC “practical” columns and built during Dutch beams as confi nement. The term occupation, slight- “practical” is used because the ly damaged due to specs are not based on any calcu- lack of mainten- lations and are adopted as a stan- ance in Nias. dard practice. The shop houses are built according to prevailing practice by contractors and foremen, without structural analysis or drawings. In neither Nias or Simeulue was the building permit system enforced; 4 EERI Special Earthquake Report — August 2005 Figure 13. “Pancake” type of collapse of shop houses Figure 14. Another pancake collapse in Gunung that killed many people in Teluk Dalam, Nias. Sitoli, Nias. therefore no structural check was tenance (Figure 11). These types of the fi rst story is completed. Only af- performed to catch poor-quality buildings are not built anymore be- ter several months or years, when materials or poor workmanship. cause of the lack of expertise in this more funds are available, do the generation, and because they are too second-story columns and walls get Timber houses consist of a timber costly to build. The other buildings, built; the process of constructing the frame and timber plank walls, and built by the Dutch some 150 years fi rst story is essentially repeated. galvanized iron sheet or thatch ago (Figure 12), are also earthquake- Some people continue the process roofs. In spite of the closeness to resistant when properly maintained. for the third and fourth stories. Col- the epicenter of the earthquake, the umn reinforcements and stirrups are damage was not signifi cant in rea- Causes of collapse: The main not suffi cient if the structure works sonably built timber structures. Very causes of collapse in the two to four- as an open frame, particularly in the few one-story timber houses col- story shop houses were poor mate- longitudinal direction. lapsed during the earthquakes. The rials and poor workmanship, exacer- damage that occurred resulted from bated by the prevailing procedures In the damaged structures we deterioration of the poorly main- of building in stages, depending on looked at, the length of the column tained columns (see Figure 9). In the availability of funds. The long splices for the upper fl oors con- addition, some timber columns intervals between the construction struction was generally insuffi cient, were not anchored to the founda- of various elements result in weak and the concreting at the splices tion.