Although an earthquake cannot be predicted, high magnitude quake potential in southern Java must be anticipated.
By
·4 minutes read
Antara Foto/Yulius Satria Wijaya
Evacuees affected by the Lebak earthquake occupy an emergency tent from tarpaulin at the Nirmala tea plantation, Citalahab, Malasari village, Nanggung, Bogor regency, West Java, Thursday (25/1). As many as 378 people of Malasari village take shelter in the emergency tents built by the Indonesian Military and National Police. Meanwhile, the dozens of people that did not get a place in the tents made tents from tarpaulin in the middle of the tea plantation.
JAKARTA, KOMPAS — Aftershocks continue in the Indian Ocean in the southwest of Lebak regency, Banten. Although their frequency and intensity have decreased, the tectonic activity in southern Java must serve as a lesson to increase public alertness. Moreover, the 6.1 magnitude earthquake on Tuesday (23/1) has damaged 2,700 buildings.
Based on data from the Meteorology, Climatology and Geophysics Agency (BMKG) until Friday (26/1) night, 55 aftershocks were recorded. “Two strong quakes were recorded on Friday at 5.1 magnitude around 11:48 a.m. and at 5 magnitude around 5:12 p.m.,” said BMKG earthquake and tsunami center head Mochammad Riyadi.
BMKG earthquake and tsunami early warning head Daryono said there is little chance for a bigger quake in the same zone around Lebak. “The tremor today [Friday] is classified as aftershock from the major 6.1 magnitude quake on Tuesday,” he said.
Bandung Institute of Technology (ITB) earthquake researcher Rahma Hanifa said the earthquake in Lebak needed to be connected a series of quakes in southern Java since a 7.8 magnitude quake in Pangandaran triggered a tsunami in 2006.
“After the Pangandaran quake, there were two quakes in Tasikmalaya in 2009 and 2017. Now, one has occurred in Lebak. We suspect this quake is part of the series of quakes,” she said.
Beyond normal
A study by Endra Gunawan and Rahma from ITB found a growing trend in tremor activities in southern Java after the one in Pangandaran in 2006.
“Every time there is big quake, there will be aftershocks to stabilize. However, our research found the series of quake in the area were beyond normal. Usually, an earthquake in the megathrust zone with a magnitude of 7.8 scale needs five years to stabilize. But, Pangandaran took longer,” she said.
Rahma said, so far, we cannot predict when stronger earthquakes would occur. However, she suggested readiness and anticipation of the worst condition. Moreover, from the quake on Tuesday whose scale was medium, its impact was big. “It shows our weak readiness [for quake],” she added.
National Disaster Mitigation Agency (BNPB) spokesman Sutopo Purwo Nugroho said the quake on Tuesday affected 73 districts in 9 regencies/cities in West Java, Banten and Jakarta. One was killed and 11 were injured.
As many as 2,760 houses were damaged, including 291 with severe damages, 575 with medium damages and 1,894 light damages. From that number, most of them were in Lebak and Sukabumi regencies.
As a result, many residents evacuated. After the aftershocks, the number of evacuees increased from 200 families to 300. They evacuated to tents and posts prepared by the BPBD Sukabumi.
The aftershocks on Friday made people worried. “Residents whose houses cracked due to the quake on Tuesday decided to evacuate,” BPBD Sukabumi emergency and logistics head Maman Suherman said.
In Lebak and Pandeglang, Banten, residents were calmer to face the aftershocks yesterday. Endan Hudri, 52, a resident of Bayah district, Lebak, said local people were not panicked.
Momo, 68, a resident of Saketi district, Pandeglang, said the same thing. “I got used to [quake]. I was panicked during the quake earlier,” he said.
Aside from houses, Sutopo said, the quake on Tuesday also caused damages to 85 public facilities such as houses of worship, health clinic, school, government offices and others.
Huge energy potential
Riyadi said learning from the Lebak quake, the alertness over quake potentials in southern Java must be improved. Riyadi said the quake zone in southern Java tended to be active and offered huge energy potential. According to National Earthquake Danger and Source Map 2017, the quake potential from the megathrust zone or giant plate in southern Java could reach 8.7 magnitude.
“The important lesson taken from the Lebak quake is that people in Jakarta need to be aware that their area could be affected,” Riyadi said.
Aside from the megathrust zone in southern Java, the threat potential for Jakarta can come from Sunda Strait. In 1903, there was huge earthquake of 8.1 magnitude.
Jakarta is highly prone to earthquake. Aside from many high-rise buildings, the solid rock of Jakarta’s soil is deep under the surface. Consequently, if there is an earthquake, it would amplify the shaking. “The impact would be more damaging if there is land plate near Jakarta,” he said.
During a discussion at BMKG, Public Work and Housing Minister Basuki Hadimuljono stressed the importance of calculating disaster risk in the development of infrastructure. “We have already had a new map of quake potential. Although it will increase the development cost, this map must be a reference for all infrastructure developments,” he said.
