At 05:53 hrs on 27th May 2006, an earthquake measuring 5,9 on the Richter Scale (BMG) struck Yogyakarta and some parts of Central Java. The epicentre was located approximately 3,8 kilometres south of Yogyakarta. The earthquake impacted eight districts within Yogyakarta and the neighbouring Central Java Provinces, severely damaging housing and infrastructure. The two worst-affected districts were Bantul, in Yogyakarta, and Klaten in Central Java. About 6,234 people were reported dead, and 30,000 injured. An estimated 650,000 were displaced, as some 135,000 houses were damaged or destroyed.
The Prambanan Temple Compounds, inscribed on the World Heritage List in 1991 and located a few kilometres North East of Yogyakarta, was severely affected by the earthquake. The main enclosure of Prambanan contains three temples decorated with reliefs illustrating the epic of the Ramayana, dedicated to the three great Hindu divinities (Shiva, Vishnu and Brahma) as well as three minor buildings dedicated to the animals who serve the deities (“Vahana” or Vehicles). Around the main enclosure are numerous other structures and Temples. The President of the Republic of Indonesia, H. E. Mr. Susilo Bambang Yudhoyono, visited the site with the Minister for Culture and Tourism, Mr. Jero Wacik, on Tuesday, 30 May 2006. On this occasion, the President called for UNESCO’s assistance towards the rehabilitation of the World Heritage site. In the mean time, the main enclosure of the Temple Compounds had been closed to the public.
Indeed, immediately after the earthquake, and in consultation with the Indonesian authorities, the World Heritage Centre dispatched to the site an expert in historic structures, Prof. Giorgio Croci, to assess the damage suffered by the Temples as well as the remaining risks for the structures and visitors. The mission took place from 7 to 10 June 2006, and benefited from the full assistance of the Indonesian Ministry of Culture, as well as of the UNESCO Office in Jakarta.
The report of the mission indicates that all of the structures have suffered, to different degrees, from an enlargement of the vertical joints with consequent outward deformations, cracks in some stones, collapse of some ratna (small stupa) and of parts of the balustrades, inclination of the top pinnacle, etc. Some Temples were particularly affected. Among these were the Sojiwan Temple, which was under restoration when the earthquake struck; the Plaosan Temple, where large portions of the roof have collapsed; the gates of the Compound, which have fallen down; and the so-called Sewu Temple, located outside of the main enclosure, where the outward deformations are particularly pronounced and wide cracks have opened at the four corners. With the possible exception of the Sewu Temple, the standing structures of the Temples do not appear at imminent risk of collapse. However, some risk for the security of people was noted in numerous places, mostly due to stone fragments in unstable position.
The mission examined as well the dynamic of the deformations that took place during the earthquake, taking into account the very important structural interventions that had been carried out at the Temples over the second half of the past century. These, in fact, had completely altered the structural behaviour and original constructive characteristics of the monuments. Indeed, starting from the 1950s, many of the Temples had been dismantled and rebuilt around a cage of reinforced concrete. Stones were reassembled using mostly a dry masonry technique reinforced in the joints by the injection of cement or resins. The reinforced concrete frame and the dry masonry (partially strengthened by injections) behave very differently in the event of a horizontal thrust (typical of earthquakes) since the former has a good strength but a large elastic (reversible) deformability, while the latter has a limited strength (limited by the friction between the blocks) and huge stiffness. It would appear, indeed, that the different elastic modules of these two structures are one of the main causes for the damage suffered by the Temples. This is because the deformation of the stone masonry, and in certain cases its collapse, were enhanced by the much wider deformations of the reinforced concrete grid. The latter, owing to its intrinsic structural features, did not start “working” under stress until the stones had already been deformed by the seismic action, but then contributed to the instability of the ancient monument by hitting like a hammer on the masonry, thus causing broader deformation and in same cases the collapse of the stones. In the end, the assessment has shown that under seismic action the presence of the reinforced concrete frames inside the Temples may have been not only useless, but indeed negative.
This hypothesis, if verified by the necessary detailed seismic analysis that must be carried out, will determine the possible long term remedial measures to be implemented. A credible conservation intervention, indeed, will have to be based on a detailed study of the seismic behaviour of the two structures (reinforced concrete and masonry), possibly by the development of mathematical models, combined with a very precise survey of the situation of each structure of the Compound. This will certainly require some time, and substantial resources and expertise.
In the short term, however, the mission identified some simple but essential steps to reduce the remaining risks and ensure the safety of the staff of the Ministry of Culture and visitors alike. These steps include the elimination of local risks related to unstable blocks and fragments, etc. which could fall down with obvious risks to people and workers; and the reduction of the risk of collapse for certain structures, mainly the Sewu Temple, including by means of pre-stressed belts in special fibres that must be fixed around the endangered buildings.
Based on the assessment carried out by Prof. Croci, the Indonesian authorities developed and submitted, on 22 June 2006, a request of emergency assistance, for an amount of USD 75,000, to carry out the two above urgent measures. At the time of writing of the present report (30 June 2006), the request had been approved by the Chairperson of the Committee and the corresponding funds were being decentralised to the UNESCO Office in Jakarta for implementation.
In the long term, the incompatibility of the reinforced concrete structure with the original masonry of the Prambanan Temples will have to be carefully considered, taking also into account their being nowadays part of the “history”of the monument and of conservation sciences in general. Removing these structures from all the Temples, indeed, would be an extremely radical, complex and costly operation that other priority needs might not justify. At the same time, the negative role of the cement contained in the concrete, source of salts carried by water and crystallizing on the surface of the stones during evaporation, will certainly require a solution. The extensive use of epoxy resins and water repellent based on silicon resins, practiced until today, will also need to be reconsidered. In summary, the earthquake has caused significant damage to this World Heritage property, and opened a number of conservation issues that will have to be dealt with over the next years, once the immediate risks have been mitigated.