Could Bandung's Earthquake Swarm Lead to a Bigger Quake?

September 17, 2026 | 12:00 pm

TEMPO.CO, Jakarta - A series of earthquakes in Pangalengan, Bandung Regency, West Java, Indonesia, has raised questions about whether the activity could signal a larger earthquake.

However, Daryono, an academic expert and member of the Indonesian Association of Disaster Experts (IABI), said an earthquake swarm does not necessarily mean a major earthquake is coming.

"Swarm does not always mean the earthquakes will continue to grow. Some swarm sequences can gradually subside," Daryono said in Bandung on Thursday.

Data from Indonesia's Meteorology, Climatology and Geophysical Agency (BMKG) recorded dozens of earthquakes in and around Pangalengan since Wednesday, September 16, some of which were felt by residents.

The activity continued into Thursday morning. One of the latest earthquakes had a magnitude of 2.6 and struck at 4:59 a.m. local time. The earthquake was recorded on land about 23 kilometers south of Bandung Regency at a depth of 3 kilometers.

What Is an Earthquake Swarm?

An earthquake swarm is a series of repeated earthquakes occurring in the same area over a certain period without a single earthquake, known as a mainshock, clearly dominating the sequence.

Daryono said an earthquake swarm indicates deformation and the release of stress in the Earth's crust. However, the phenomenon can be associated with several processes, including movement along a fault as well as volcanic or hydrothermal activity.

"Swarm patterns must be assessed using continuous seismological data, not simply based on the number of earthquakes," he said.

So, Does an Earthquake Swarm Mean a Bigger Earthquake Is Coming?

Not necessarily. According to Daryono, an increase in swarm activity alone cannot be used to conclude that a major earthquake will occur. Some earthquake swarms can gradually weaken without being followed by a larger event.

Pangalengan is located in southern West Java, an area with complex crustal deformation and close to the Garsela Fault system, or the South Garut Fault, one of the active fault structures with seismic activity in West Java.

The depth of an earthquake can also affect how strongly it is felt. A relatively shallow earthquake can produce noticeable shaking even when its magnitude is small. Local geological conditions can further influence the intensity of shaking experienced by residents.

What Should Residents Do?

Daryono urged residents not to panic but to remain prepared by checking the condition of buildings, securing furniture and other objects that could fall, and learning the "drop, cover, and hold on" procedure for when an earthquake occurs.

"Therefore, people do not need to associate every increase in earthquake swarm activity with the possibility of a major earthquake. The most important thing is to remain alert and follow official information," he said.

He also warned that earthquakes can trigger secondary hazards, such as landslides. Residents around Pangalengan should therefore continue monitoring official information and updates on seismic activity from BMKG.

Indonesia's Bandung Earthquake Swarm Continues Into Thursday Morning

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