BMKG details Flores M7.7 earthquake, tsunami and aftershock surveys

Labuan Bajo — Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) confirms that a magnitude 7.7 earthquake struck north of Flores, East Nusa Tenggara, on Saturday, 15 August 2026, triggering a tsunami recorded across four provinces and a sustained sequence of aftershocks.

BMKG’s updated analysis places the mainshock at 04:58:23 WIB (05:58:23 WITA) at a depth of 15 kilometres, classifying it as a shallow tectonic earthquake with tsunami potential. The agency’s modelling led to an immediate tsunami early warning for coastal areas of East Nusa Tenggara, West Nusa Tenggara, South Sulawesi and Southeast Sulawesi.

According to BMKG’s summary on 17 August, preliminary field information indicated at least 53 fatalities and 137 injuries across districts including West Manggarai, Manggarai, East Manggarai and Sikka, including Maumere, with damage ranging from light to heavy.

Fault setting and shaking impacts

BMKG identifies the Flores earthquake as a shallow tectonic event associated with the regional Flores back-arc setting, which produces strong ground shaking near populated coastlines. In its public statements the agency describes upward movement and significant deformation of the seafloor as the mechanism responsible for tsunami generation, but detailed parameters such as rupture length, slip and recurrence intervals have not yet been published.

BMKG emphasises that for communities, infrastructure and tourism along the northern Flores coast, the immediate priority is the safety of buildings and ground conditions after the main shock rather than predicting the exact timing of future events. Residents are advised to avoid structures that are cracked or visibly damaged and to remain alert to ongoing aftershocks.

The agency is coordinating with national and local government to support recovery, deploying survey teams from its headquarters and regional units to conduct macroseismic assessments, microtremor measurements, surface wave tests and verification of tsunami impacts. BMKG says these surveys are intended to map damage patterns, refine hazard understanding and inform safer reconstruction and mitigation planning in the most affected areas.

Tsunami warning and observations

BMKG issued its first tsunami early warning just over two minutes after the earthquake, based on real-time modelling that showed the potential for hazardous waves along parts of East Nusa Tenggara, West Nusa Tenggara and South Sulawesi. The agency applied a “Siaga” threat level, corresponding to estimated wave heights of 0.5 to 3 metres, for several northern coastal districts of Flores and parts of southern Sulawesi, and a lower “Waspada” level for areas where wave heights were expected to remain below 0.5 metres.

The tsunami warning was lifted at 07:30 WIB, after BMKG reported no further significant rises in sea level that would endanger coastal communities. Nonetheless, tide-gauge data and field checks confirmed tsunami waves at 16 locations across East Nusa Tenggara, West Nusa Tenggara, South Sulawesi and Southeast Sulawesi.

BMKG’s 17 August update recorded the highest instrumental tsunami height at 1.605 metres at Pota, East Manggarai, at 05:03 WIB, and the lowest at 0.14 metres at Bakalang, Alor, at 05:41 WIB. Subsequent tsunami run-up surveys reported maximum inundation heights of up to 2.68 metres along parts of the north Flores coast, with waves penetrating around 145 metres inland at some sites.

Aftershock sequence and monitoring

BMKG reports an intense aftershock sequence following the mainshock. By 11:00 WIB on 17 August, the agency had detected 1,624 aftershocks with magnitudes between 1.3 and 6.2, of which 24 events exceeded magnitude 5 and 70 were felt by residents.

A subsequent BMKG release noted 2,119 aftershocks by 05:00 WIB on 18 August, again in the magnitude range of 1.3 to 6.2. Later briefings from BMKG officials indicated that more than 13,000 aftershocks were recorded in the first month after the earthquake, underlining the need for continued caution around damaged structures.

BMKG’s provisional assessment is that the aftershock activity is expected to decrease significantly after several weeks, although individual events cannot be predicted with precision. The agency urges residents, visitors and businesses in Flores and neighbouring islands to rely on official information channels and to incorporate updated hazard maps and survey findings into reconstruction and future development plans.

Sources

• BMKG – Gempa Bumi M7,0 – 38 km TimurLaut MBAY-NAGEKEO-NTT
• Bloomberg Technoz – BMKG Temukan Jejak Tsunami Flores hingga 2,68 Meter
• IDN Times – Gempa Magnitudo 7,7 di Flores Berpotensi Tsunami, Status Siaga
• BBC News Indonesia – Gempa NTT: Jumlah korban tewas jadi 103 orang – Apa yang diketahui sejauh ini?
• RRI – BMKG Records 13,863 Aftershocks After Flores Earthquake
• ObserverID – Flores Aftershocks Subside, BMKG Unveils Field Survey to Guide Recovery