BMKG Reveals The Trigger For The Concrete Earthquake On Mount Salak

BMKG Seismologist Pepen Supendi in socialization of disaster mitigation and seismicity in Pamijahan, Bogor Regency, West Java, Tuesday (4/11/2025). BETWEEN/M Fikri Setiawan

BOGOR - The Meteorology, Climatology and Geophysics Agency (BMKG) revealed that the successive earthquake that rocked the Mount Salak area on September 20 was caused by Cianten Fault activity, part of the Bayah Fault system, with tectonic character, not volcanic.

BMKG seismologist Pepen Supendi explained that the results of the seismic wave analysis and mapping of the Geological Agency showed that the earthquake in the area came from a shift in the soil layer due to active fault activity.

"From the character of the wave, it is clear that this is a tectonic earthquake due to active faults, not due to magma activity," said Pepen Supendi as quoted by ANTARA, Tuesday, November 4.

He said, the Cianten Fault segment crosses the Pamijahan District to the western and eastern parts of Mount Salak, so it is natural that this area often experiences small earthquakes.

According to Pepen, with the increasing number of seismic stations to more than 550 units throughout Indonesia, BMKG is now able to record small vibrations more accurately than in the past.

"In the past, it was like catching a big fish. Now the net is tight, small earthquakes can be detected," he said.

He added, not all small earthquakes indicate a large potential danger. The impact is very dependent on the condition of the ground and the strength of the building on the surface.

Disaster Expert Budi Pranowo, who is also the former Secretary of the Bogor Regency BPBD, explained that small earthquakes such as Mount Salak actually function as an underground energy release in stages.

Yesterday's earthquake averaged below a magnitude of 3.5. It's like a small drift, the energy comes out little by little so it doesn't pile up into a big earthquake," he said.

He revealed that the main earthquake on September 20, 2025, had a magnitude of 3.2 with 43 aftershocks of smaller intensity. This phenomenon is quite natural in geologically active areas.

Budi also mentioned historical records of earthquakes in the region, including earthquakes measuring 4.8 magnitudes in 2012 in Cibubian, which resulted in damage to dozens of residents' houses.

"If you look at the characteristics, this area is already an active fault route. Therefore, people must get used to it and not panic when an earthquake occurs," he added.

BMKG emphasized that tectonic earthquakes around Mount Salak were not related to volcanic activity or geothermal operations. All data shows that energy sources originate from active fault shifts.

Pepen Supendi reminded that people need to get used to following safety guidelines such as not panicking, looking for open spaces, and paying attention to the structure of the surrounding buildings.

The Bogor Regency Government through BPBD in collaboration with BMKG and Star Energy continues to disseminate and educate disaster mitigation so that people understand the actions just before, when, and after the earthquake occurred.