JAKARTA, KOMPAS – The threat of a large earthquake from the subduction zone under the south Java Indian Ocean is nearing its cycle. The earthquake measuring a magnitude of 6.9 on the Richter scale, with an epicenter in Tasikmalaya, West Java that struck on Friday should be seen as a warning to raise alertness.
Research by the Indonesian Institute of Sciences (LIPI) has discovered three giant tsunami recurrences, thought to have been triggered by an earthquake from the southern Java subduction zone.
“We have found traces of giant tsunamis in southern Java, that date back 500, 1,000 and 1,800 years, respectively,” said Purna S Putra, a paleotsunami researcher at LIPI Geotechnology Center, Sunday.
In light of this data, it is suggested that a giant earthquake, followed by a tsunami in southern Java, occurs on a cycle of once every 500 to 800 years. The recurrence period of large earthquakes in Sumatra, meanwhile, is 512 years - the earthquake that was followed by a tsunami in Aceh in 2004 is proof of this.
Bandung Institute of Technology (ITB) earthquake expert Irwan Meilano is also concerned about the potential for a large earthquake in southern Java. The potential for a large earthquake in southern Java has been included in the revised 2017 national earthquake map.
Irwan, who is also the head of the 2017 National Earthquake Map Revision Team’s geodesy work group, said a potential earthquake in southern Java could reach a magnitude of 8.7. However, if the earthquake segment in this area simultaneously collapsed, the magnitude could reach 9.2.
ITB Civil Engineering professor and head of the National Earthquake Study Center, Masyhur Irsyam, said the earthquake potential from the Sunda Strait and southern Java subductions must be dealt with swiftly in order to mitigate the impacts. “It is extremely urgent for all of us to identify the subduction threat,” he said.
For the purposes of mitigation, Masyhur recommended that the government carry out a detailed study of plate movements in the Sunda Strait and southern Java subduction zones. “From there, we would have a better ability to anticipate future subduction earthquakes,” he said.
The quality of buildings also needs to be improved. According to Masyhur, most buildings in Indonesia have not been built to withstand earthquakes. This was evidenced by the massive damage caused by the Tasikmalaya earthquake.
Three people killed
The impact of the 6.9 magnitude earthquake in Tasikmalaya was worse than initially predicted. On Saturday, three people were recorded to have died, while seven people were injured and 722 houses were damaged. According to the latest data from the National Disaster Mitigation Agency (BNPB), as of Sunday, the earthquake had killed four people, severely injuring 11 people and causing minor injuries to 25 people. In terms of damages, meanwhile, as many as 451 houses were left severely damaged, 579 houses suffered medium-scale damages and 1,905 houses were left with minor damages.
Furthermore, 46 schools/madrasah, 38 places of worship and four hospitals and puskesmas (community health centers) were also damaged. As many as 200 people were evacuated to Pamarican district, Ciamis regency. “Data collection is still being done. The number of damaged (buildings) is expected to rise,” said BNPB spokesperson Sutopo Purwo Nugroho.
According to Sutopo, the areas that suffered the most damage were Tasikmalaya city, Tasikmalaya regency, Ciamis regency and Pangandaran regency. These areas were the closest to the earthquake’s epicenter.
Masyhur Irsyam said the earthquake was of a relatively small magnitude, and would not have caused much damage had the buildings been built with quake-proof structures.
Given its earthquake-prone location, Masyhur said buildings in Indonesia must be built to be quake-resistant. The Public Works and Public Housing Ministry has issued guidelines for making quake-proof public houses. “Local administrations must be involved in supervising the development in their respective regions. The monitoring of building strength should be done in line with the IMB (building construction permit) standards,” he said.
Emergency response
Following the Tasikmalaya earthquake, emergency response operations have continued to be carried out. Yesterday, BNPB head Willem Rampangilei held a coordination meeting with regional heads, regional disaster mitigation agencies (BPBD), the Social Affairs Ministry and local authorities in Tasikmalaya and Ciamis. Four priorities were identified as needing to be addressed: the addition of logistic aid, repairs of damaged settlements, financial assistance and repairs of public facilities and infrastructure.
Tasikmalaya regency Disaster Mitigation Agency (BPBD) head EZ Alfian said that the agency has been distributing logistic aid, such as rice and instant noodles to the victims of the earthquake. At the moment, the agency is focused on rescue efforts to save local residents, particularly those whose houses have been damaged so that they do not become stranded.
“For the people whose houses have been severely damaged and cannot be lived in, we will help find a place that can accommodate them. Most of the people whose houses have been damaged evacuate to the houses of their relatives,” he said.
In the last couple of days, Ciamis regency Disaster Mitigation Agency (BPBD) has set up two evacuation posts in Pamarican, the worst affected area out of the 22 districts in Ciamis regency. Of the 1,104 damaged houses in Ciamis, 558 of them were in Pamarican. As many as 254 people have been evacuated temporarily either to evacuation posts or a relative’s house. Health and kitchen posts have also been set up.
(AIK/IKI/BKY/SEM/DMU)
