BMKG says Flores aftershocks top 15,700 in first month and urges vigilance

Flores Island — Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) has confirmed that 15,722 aftershocks were recorded in Nusa Tenggara Timur during the 30 days following the 15 August 2026 main earthquake off northern Flores, and says activity is now declining but not yet over. According to BMKG, residents in Flores and surrounding districts are urged to remain vigilant even as most recent tremors are relatively small.

In a briefing summarised by several Indonesian media outlets, BMKG acting deputy for geophysics Ardhasena Sopaheluwakan said that up to 15 September 2026 at 05:00 Western Indonesian Time, the agency’s seismic network had detected 15,722 aftershocks with magnitudes ranging from 0.9 to 6.2. He noted that 190 of these events were felt by residents, while the vast majority were only detected by instruments.

Local coverage from Kupang reported BMKG’s findings that earthquakes below magnitude 3.0 dominate the sequence, accounting for 11,993 events, or about three quarters of the total. BMKG explained that these smaller tremors typically do not cause damage and are often not felt by people, but they remain part of the ongoing adjustment of the crust after the 7.7‑magnitude mainshock of 15 August.

National outlets citing the same BMKG dataset also highlighted that the daily and weekly number of aftershocks has begun to fall, indicating the sequence is entering a decay phase. BMKG described a consistent downward trend in the frequency of events compared with the first days after the mainshock.

Earlier BMKG updates in late August had reported 9,765 aftershocks by 30 August, with a maximum magnitude of 6.2 and the smallest events near magnitude 1.0, underscoring how quickly the number of recorded tremors grew in the first two weeks. By mid‑September, the agency’s analysis shows the rate of new events slowing, though still significantly above normal background levels for the region.

BMKG’s overview places the ongoing aftershocks across northern Flores and wider Nusa Tenggara Timur, following the powerful 7.7‑magnitude earthquake that struck offshore to the north of Flores on 15 August 2026. The agency’s bulletins and press conferences emphasise that this area remains seismically active and that further small to moderate tremors are expected as the sequence continues.

In its latest communication, BMKG advises communities in Flores, including Manggarai and Manggarai Barat, and across Nusa Tenggara Timur to stay alert to official information channels and to ensure preparedness measures remain in place. The agency calls on residents, local governments and businesses to review evacuation routes, secure buildings and infrastructure where possible, and avoid spreading unverified information about earthquakes.

BMKG also stresses that while the probability of another major shock decreases over time after a large event, it cannot be ruled out entirely. Authorities therefore recommend that people living and working in coastal and hilly areas of Flores follow established disaster‑risk guidance, including knowing safe locations and being ready to move quickly if strong shaking is felt.

Sources

• POS-Kupang / Tribunnews NTT
• Bloomberg Technoz
• RRI