Daryono: Pangalengan Earthquakes Are Not a Definite Sign of a Major Quake
Seismic activity has increased again in the Pangalengan area, Bandung Regency, West Java. Dozens of earthquakes have been recorded since Wednesday (16/9), some of which were felt by the public. This phenomenon is categorised as an earthquake swarm. Daryono, a member of the Indonesian Disaster Expert Association (IABI), stated that an earthquake swarm is a series of earthquakes occurring repeatedly in a specific area and period, without a single mainshock clearly dominating the sequence.
“However, the presence of a swarm does not, in itself, indicate that tectonic energy is being released exhaustively or that a large earthquake will definitely occur,” said Daryono on Thursday (17/9).
According to data from the Meteorology, Climatology, and Geophysics Agency (BMKG), an earthquake occurred in Pangalengan on Thursday (17/9) at 04:59 WIB with a magnitude of 2.6. The epicentre was located at coordinates 7.22 degrees South Latitude and 107.60 degrees East Longitude, on land approximately 23 kilometres south of Bandung Regency, at a depth of three kilometres.
Daryono noted that this activity pattern needs to be analysed based on several parameters, including epicentre distribution, depth, source mechanism, activity migration, and temporal and spatial changes.
He explained that Pangalengan is located in the southern part of West Java, which possesses a fairly complex crustal deformation. The area is near the Garsela (Garut Selatan) Fault system, one of the active fault structures identified as having seismic activity in West Java.
Furthermore, Daryono stated that shallow earthquake activity in the region should be viewed as part of a complex regional tectonic system. The subduction process of the Indo-Australian Plate beneath the Eurasian or Sunda Plate south of Java results in the accumulation and redistribution of stress within the Earth’s crust, some of which is released through movements in active faults.
Daryono explained that shallow earthquakes can produce relatively strong shaking on the surface despite having low magnitudes, because seismic energy is released relatively close to the surface. “Small magnitude does not always mean the shaking will be unnoticeable,” he said.
In addition to the depth of the source, the level of shaking felt by the public is also influenced by local geological conditions. Relatively soft sedimentary layers or volcanic materials can amplify ground movement at certain frequencies.
Dary’ono emphasised that the emergence of an earthquake swarm in Pangalengan does not mean the earthquakes will continue to grow in size. Some swarm sequences can subside gradually, so their development must be monitored through continuous seismological data.
“A swarm is not a sign of a major earthquake. There is no scientific basis to state that this sequence will definitely lead to a large earthquake,” he asserted.
He reminded the public not to respond to the earthquake series with panic, but to maintain increased preparedness. The public is advised to ensure buildings are in good condition, secure furniture that could easily fall, know safe locations, and understand the ‘drop, cover, and hold on’ procedure during tremors.
“Do not panic because of the swarm, but do not be careless either. Understand the earthquake, strengthen your buildings, and prepare the community,” concluded Daryono.