2006 Yogyakarta earthquake

2006 Yogyakarta earthquake
Jakarta
Pangandaran
Yogyakarta
Date 27 May 2006 (2006-05-27)
Origin time 05:54 local time [1]
Magnitude 6.4 Mw [1]
Depth 15 km (9 mi) [1]
Epicenter 8°04′S 110°21′E / 8.07°S 110.35°E / -8.07; 110.35Coordinates: 8°04′S 110°21′E / 8.07°S 110.35°E / -8.07; 110.35 [1]
Type Strike-slip
Areas affected

Yogyakarta Special Region

Java, Indonesia
Total damage Extreme [2]
Max. intensity IX (Destructive) [3]
Peak acceleration .336g [4]
Casualties 5,749–5,778 dead [5]
38,568–137,883 injured [5]
600,000–699,295 displaced [5]

The 2006 Yogyakarta earthquake (also known as the Bantul earthquake) occurred at 05:54 local time on 27 May with a moment magnitude of 6.4 and a maximum intensity of IX (Destructive) on the Medvedev–Sponheuer–Karnik scale. The shock occurred on the southern coast of Java near the Indonesian city of Yogyakarta, and caused a disproportionate number of casualties, with more than 5,700 deaths, tens of thousands injured, and financial losses of Rp 29.1 Trillion ($3.1B). The United States' National Geophysical Data Center lists the total damage from the event as extreme.

Previous volcanic deposits and lahars that flowed off Mount Merapi were found to have amplified the intensity of the shaking and created the conditions for soil liquefaction to occur, but the concurrent activity on the stratovolcano was not directly connected with the earthquake. With a lack of instruments in the area, the shock was initially attributed with the Opak Fault that lies to the east of the affected areas, but later InSAR analysis revealed that another previously unknown fracture was responsible for the sequence of shocks.

Tectonic setting

The islands of Indonesia constitute an island arc that is one of the world's most seismically active regions, with high velocity (up to 60 mm (2.4 in) per year) plate movement at the Sunda Trench, and considerable volcanic activity throughout. The south central portion of the island of Java (one of the five largest in the Indonesian archipelago) had been affected by an eruption of Mount Merapi that began prior to the May 27 earthquake, but the Special Region of Yogyakarta has experienced numerous other eruptions, earthquakes, and tsunamis, including the Pangandaran earthquake and tsunami that occurred just two months later. Java lies on the Sunda Shelf (and the Sunda microplate) to the north of the Sunda Trench, which is a convergent plate boundary where the Indo-Australian Plate is being subducted under the Eurasian Plate. The subduction zone is characterized by frequent earthquakes and a large number of active volcanoes that influence the regional geography, and due to direct or indirect stress transfer, the offshore plate movement has affected the various onshore faults that are closer to the Special Region of Yogyakarta.[6]

Earthquake

USGS ShakeMap for the mainshock

According to the United States Geological Survey (USGS), the shock occurred 20 km (12 mi) south-southeast of Yogyakarta at a depth of 10 km (6.2 mi), but other institutions provided source parameters (location and depth) that were not in agreement. No information was present on the extent of the faulting or the direction of propagation, but the shock was unlikely to be related to the eruption of Mount Merapi. The USGS suggested that the focal mechanism was most likely associated with left-lateral slip on a NE–SW trending strike-slip fault, as that is the orientation of the Opak Fault, but this has not been validated. No surface breaks were documented, but the location of the greatest damage that was caused does align with the Opak Fault as a possible source.[7]

A group of Japanese and Indonesian scientists visited the area in March 2007 and confirmed the lack of surface ruptures, and pointed out that any visible expression of the fault would likely have been rapidly destroyed due to the tropical climate, and have acknowledged the widely varying locations (and the preference for the Opak Fault) that were reported by the various seismological institutions. Their investigation resulted in a different scenario, with an unknown or newly formed NE–SW trending fault as the origin of the shock. Evidence for one of the proposed faults was found in the form of alignment of portions of the Oyo River near the USGS' epicenter, which is parallel (N°65E) to the Nglipar fault in the southern mountains region. If the shock occurred in this area it could indicate the reactivation of a major fault system. The second proposed fault further to the east is nearly parallel to the Nfalang and Kembang faults that lie to the north of the Oyo River.[8]

InSAR analysis

Further information: Remote sensing

While the densely populated area that saw significant destruction is adjacent to the Opak River Fault, both the USGS and Harvard University placed the epicenter to the east of that fault. Few seismometers were operating in the region, but a group of temporary units that were set up following the mainshock recorded a number of aftershocks that were east of the Opak River Fault and were aligned along a 20 km (12 mi) zone striking N°50E. Due to the ambiguous nature of the available information on the source of the Yogyakarta earthquake, a separate group of Japanese and Indonesian scientists applied one of the first uses of Interferometric synthetic aperture radar (InSAR) to determine the source fault. Several data sets (one captured in April 2006 and another post-earthquake batch from June) were collected from an instrument on board the Advanced Land Observation Satellite and were compared to each other to show potential ground deformation patterns.[9]

Unrest at Mount Merapi in June 2006

A lack of any dislocation found on the images along the Opak River fault made evident the lack of movement along that fault, and though the aftershocks were occurring at a depth of 8–15 km (5.0–9.3 mi), the deformation was distinct at the surface. The observed ground deformation that was detailed by the differential satellite images and Global Positioning System measurements was roughly 10 km (6.2 mi) east of (and parallel to) the Opak River Fault, along a zone that passed through the USGS' epicenter, and delineated a fault with a strike of N48°E and a dip of 89°. The displacements were not more than 10 cm (3.9 in) and indicated left-lateral strike-slip motion as well as a component of reverse slip, and to the west of the Opak River Fault (and closer to the areas of damage) strong ground motion triggered subsidence of volcanic deposits from Mount Merapi.[9]

Strong motion

In 2006, Mount Merapi had not been active for more than four years, but on May 11 a pyroclastic flow triggered the evacuation of more than 20,000 people from the northern sector of Yogyakarta. While authorities expected a larger eruption to follow, the earthquake occurred instead. The volcano's previous eruptions deposited loosely bound sedimentary material in the valley during lahar flows. Following the mainshock, German and Indonesian scientists set up instruments at several locations situated on different soil types to measure aftershocks. Of nine events that were analyzed, it was found that the station at Imogiri (a heavily affected village that was built on 150–200 meters (490–660 ft) of sediment) showed signs of local amplification when compared to a location that was built on bedrock, and that the deposits amplified the impact of the earthquake.[10]

Liquefaction

See also: Kewu Plain

A separate post-event study looked at the relationship with the layer of sediment and the occurrence of soil liquefaction during earthquakes near Bantul. Researchers stated that the Yogyakarta region is seismically active, with four known events in the 19th century and three in the 20th century, with peak ground acceleration values of 0.038–0.531g. The type and properties of sediment control the occurrence and distribution of liquefaction, and other environmental conditions (like the water table) also play a part, as well as the peak ground acceleration of the earthquake. The Bantul-Klaten plain consists of alluvium (sand, silt, clay, and gravel) and volcanic deposits from Merapi (sand, agglomerates, tuff, and ash), as well as limestone and sandstone. Borehole and magnetic data surveys show that the alluvium and lahar deposits at the Bantul graben are 20–200 meters (66–656 ft) thick and at places over 200 meters, and the water table is .6–5 meters (2 ft 0 in–16 ft 5 in) below ground level. Most liquefaction events took place near the 2.5 km (1.6 mi) wide Opak Fault zone. Sand boils, lateral spreading, settling, and slides led to some tilting and collapse of buildings.[11]

Damage

Altogether, eleven densely populated districts comprising 8.3 million people were affected, but the regencies of Bantul, Sleman, Gunung Kidul, Kulon Progo, Klaten, and the city of Yogyakarta were especially hard hit. More than 5,700 people were killed in the early morning shock, with tens of thousands injured, and several hundred thousand made homeless. Total financial losses from the event are estimated to be Rp 29.1 Trillion ($3.1B), with 90% of the damage affecting the private sector (homes and private businesses) and only 10% affecting the public sector. The damage to housing accounted for about half of the total losses and a comparison was made to the damage in Aceh following the 2004 Indian Ocean earthquake and tsunami. Damage in central Java was worse because of the substandard construction practices and the high population density. On the other end of the scale, damage to infrastructure was very limited.[12]

Response

Patients being treated at a hospital in Yogyakarta.

Although Tsunami warnings were issued in the early aftermath of the earthquake, the earthquake did not cause any tsunami activity.

Political

President Susilo Bambang Yudhoyono moved the army to the central Java province to aid rescue efforts and the evacuation of victims. A team of Cabinet Ministers was also sent to oversee the operations.

International aid

Many countries and organizations offered foreign aid to the devastated region, but the actual amounts delivered/received often varied from these figures, as in the case of other disasters.

A fallen pinnacle from the damaged Prambanan temple

Media

Most international wire services had already had reporters or 'stringers' in the area due to the Mount Merapi eruption to the north of Yogyakarta.

Yogyakarta for many is associated with Borobudur and Prambanan, even though both locations are some distance away from the town. As a result, news stories tend to emphasize the condition of those places. Borobudur suffered no damage whereas Prambanan, which is much closer to the epicentre, has according to reports,[28] suffered significant damage.

The reporting of the immensity of the problems that were evolving following the earthquake also competed with the crisis in East Timor (Timor Leste) in the media of some countries like Australia and New Zealand.

Reconstruction

The earthquake's shallow depth was a major factor, but the scale of the damage was made worse by failure to meet safe building standards and employ basic earthquake-resistant construction methods, according to FuturArc.[29] Most homes in the area were built with low-quality materials without structural frames and reinforcing pillars. Many deaths and injuries occurred when buildings and walls collapsed.

The government was slow to implement assistance in reconstructing private houses, leading many homeowners to repair or rebuild their homes either by themselves or with community help. Reconstruction in some areas was aided by relief agencies, like the Red Cross Red Crescent.

Villagers rebuilt their homes with extremely limited resources, using simple affordable materials. They turned to traditional materials, such as bamboo, because of the damage inflicted by collapsing brick walls.

See also

References

  1. 1 2 3 4 ISC (2015), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 2.0, International Seismological Centre
  2. ↑ National Geophysical Data Center / World Data Service (NGDC/WDS), Significant Earthquake Database, National Geophysical Data Center, NOAA, doi:10.7289/V5TD9V7K
  3. ↑ Murakami, H.; Pramitasari, D.; Ohno, R. (2008), Human casualty and damage distribution in relation to seismic intensity in the 2006 Central Java earthquake in Indonesia (PDF)
  4. ↑ Elnashai et al. 2006, p. 18
  5. 1 2 3 USGS (September 4, 2009), PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey
  6. ↑ Marso, J.; Anderson, R.; Frost, E. (2008), "A short note on the tectonic setting and regional geology of the area affected by the May 27, 2006, Yogyakarta earthquake and its usefulness in assessing seismic hazard", The Yogyakarta earthquake of May 27, 2006, Star Publishing Company, Inc., pp. 1.1–1.3, ISBN 978-0-89863-304-7
  7. ↑ Elnashai et al. 2006, pp. 9, 15
  8. ↑ Setijadji, L. D.; Barianto, D. H.; Watanabe, K.; Fukuoka, K.; Ehara, S.; Rahardjo, W.; Sudarno, I.; Shimoyama, S.; Susilo, S.; Itaya, T. (2008), "Searching for the active fault of the Yogyakarta earthquake of 2006 using data integration on aftershocks, cenozoic geo-history, and tectonic geomorphology", The Yogyakarta earthquake of May 27, 2006, Star Publishing Company, Inc., pp. 4.1–4.4, 4.17, 4.18, ISBN 978-0-89863-304-7
  9. 1 2 Tsuji, T.; Yamamoto, K.; Matsuoka, T.; Yamada, Y.; Onishi, K.; Bahar, A.; Meilano, I.; Abidin, H. Z. (2009), "Earthquake fault of the 26 May Yogyakarta earthquake observed by SAR interferometry" (PDF), Earth, Planets and Space, Terra Scientific Publishing Company, 61: e29–e32
  10. ↑ Walter, T. R.; Wang, R.; Luehr, B.-G.; Wassermann, J.; Behr, Y.; Parolai, S.; Anggraini, A.; Günther, E.; Sobiesiak, M.; Grosser, H.; Wetzel, H.-U.; Milkereit, C.; Sri Brotopuspito, P. J. K.; Harjadi, P.; Zschau, J. (2008), "The 26 May 2006 magnitude 6.4 Yogyakarta earthquake south of Mt. Merapi volcano: Did lahar deposits amplify ground shaking and thus lead to the disaster?", Geochemistry, Geophysics, Geosystems, Wiley, 9 (5): 2, 5, 6, doi:10.1029/2007GC001810
  11. ↑ Sarah, D.; Soebowo, E. (2013), "Liquefaction Due to the 2006 Yogyakarta Earthquake: Field Occurrence and Geotechnical Analysis", Procedia Earth and Planetary Sciences, International Symposium on Earth Science and Technology, CINEST 2012, Elsevier, 6: 383–388, doi:10.1016/j.proeps.2013.01.050
  12. ↑ CGI 2006, pp. 3, 7, 12, 13, 15
  13. 1 2 3 4 "Aid pledges for Java victims rise". BBC News. 2006-05-29. Retrieved 2006-05-29.
  14. 1 2 "Aid offers pour in for Java quake". BBC News. 2006-05-28. Retrieved 2006-05-28.
  15. ↑ "U.S. Military Joins Indonesia Quake Relief". CBS News. 2006-05-31. Archived from the original on June 14, 2006. Retrieved 2006-05-31.
  16. ↑ "Australia send 80 skilled personnel to Yogyakarta". Antara. 2006-05-31. Retrieved 2006-05-31.
  17. ↑ "China to offer 2 mln dollars aid to quake-hit Indonesia". People's Daily Online. 2006-05-28. Retrieved 2006-05-28.
  18. ↑ "Ottawa pledges $2M to Indonesia quake victims; no Canadians reported affected". Maclean's. 2006-05-27. Archived from the original on June 14, 2006. Retrieved 2006-05-28.
  19. ↑ "India steps up aid to Indonesia". The Hindu. 2006-05-29. Retrieved 2006-05-30.
  20. ↑ "Mormons Donate for Indonesia Earthquake Relief". The Church of Jesus Christ of Latter-day Saints Newsroom. 2006-05-31. Retrieved 2006-05-31.
  21. ↑ "All our students in Yogyakarta safe". The Star, Malaysia. 2006-05-28. Retrieved 2006-05-28.
  22. ↑ "Singapore's aid teams arrive in quake-hit Java". Channel NewsAsia. 2006-05-28. Retrieved 2006-05-28.
  23. ↑ "UN health agency rushes aid to quake-struck parts of Indonesia". UN News Centre. 2006-05-29. Retrieved 2006-05-30.
  24. ↑ "Vietnam sends rice aid to Java quake victims". VietNamNet Bridge. 2006-05-31. Archived from the original on 2006-06-13. Retrieved 2006-05-31.
  25. ↑ "Island aid for Indonesia". Manx Radio. 2006-05-31. Archived from the original on May 6, 2006. Retrieved 2006-06-01.
  26. ↑ "King orders dispatch of aid to Indonesian Earthquake Victims". Petra News Agency (Jordan). 2006-05-31. Archived from the original on June 14, 2006. Retrieved 2006-06-01.
  27. ↑ http://www.mercy.org.my/read.php?id=24
  28. ↑ Sebastien Berger (2006-05-30). "An ancient wonder reduced to rubble". The Sydney Morning Herald. Retrieved 2006-05-30.
  29. ↑ http://www.futurarc.com/this_edition/discussion_lesson_learned.cfm

Sources

External links

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