BMKG Confirms Hundreds of Flores Aftershocks, 13,000 Total Not Verified

Flores — — Indonesia’s meteorology agency says aftershocks are still occurring following the 15 August 2026 magnitude 7.7 earthquake off Flores, but available public data does not support a cumulative total above 13,000 as of 20 September.

The mainshock struck off the north coast of Flores on 15 August, initially recorded at magnitude 7.0 and later revised to 7.7 at a depth of 15 kilometres, according to the Meteorology, Climatology and Geophysics Agency (BMKG). BMKG located the epicentre offshore near Nagekeo Regency in East Nusa Tenggara.

In its 15 August press release, BMKG reported 235 aftershocks by 14:00 WIB on the day of the quake, with magnitudes ranging from 2.5 to 6.2 and distributed north of Flores. A subsequent press statement on 17 August said BMKG had recorded 1,624 aftershocks by 11:00 WIB on that date, with magnitudes between 1.3 and 6.2. These figures confirm intense aftershock activity in the days immediately following the mainshock.

Public BMKG articles and advisories issued in early September describe the Flores earthquake as a moment to strengthen science-based disaster mitigation and review the performance of the national tsunami early warning system, without publishing a detailed, updated aftershock count in the thousands. Available open sources therefore do not corroborate a cumulative total exceeding 13,000 events by 20 September.

Aftershock activity and public guidance

BMKG’s 17 August release noted that aftershocks remained ongoing and urged residents in affected areas to stay calm but vigilant, follow instructions from local authorities and avoid damaged buildings until they were declared safe. Local and international media reporting in mid-August likewise highlighted that residents experienced numerous aftershocks, including one of magnitude 6.1, after the initial quake.

Seismologists routinely monitor both the number and rate of aftershocks. A rising cumulative count over time can be consistent with a falling daily rate of events, meaning a high total number of recorded aftershocks does not in itself indicate that another major earthquake is imminent. BMKG’s guidance has focused on practical safety measures and the use of official information channels rather than on speculative forecasts.

Key confirmed data points

• Mainshock: magnitude 7.7, 15 August 2026, offshore north of Flores at a depth of about 15 km, with a tsunami potential identified in BMKG modelling.
• Recorded aftershocks: 235 events by 14:00 WIB on 15 August; 1,624 events by 11:00 WIB on 17 August, according to BMKG press statements.
• BMKG messaging: continued aftershock activity, combined with appeals for residents to remain calm, stay away from damaged structures and follow instructions from local authorities and official information channels.

Context

The 15 August earthquake caused significant damage across parts of Flores and triggered a tsunami, according to BMKG’s post-event analysis. International and Indonesian media reported casualties and building collapses in several regencies, along with temporary tsunami warnings that were later lifted.

BMKG has framed the Flores event as an opportunity to strengthen disaster mitigation, early warning systems and resilient infrastructure, emphasizing lessons for future preparedness. While detailed, day-by-day aftershock statistics beyond 17 August were not available in the public materials consulted for this report, the agency’s advice for vigilance and reliance on official updates remains pertinent as rehabilitation and reconstruction continue in affected communities.

Sources

• BMKG – Gempa Bumi M7,0 – 38 km TimurLaut MBAY-NAGEKEO-NTT
• The Jakarta Post – At least two dead in magnitude 7.7 quake in NTT
• The Guardian – Powerful earthquake kills dozens in eastern Indonesia