What the August 2026 M7.7 Flores Sea Earthquake Reveals About Indonesia’s Seismic Risk

Magnitude Measurements from Different Agencies

Seismic monitoring agencies reported slightly different magnitude values:

• USGS: Mw 7.7 (moment magnitude) .
• BMKG (Indonesia's Meteorology, Climatology and Geophysics Agency): Initially reported as M 7.7, and also listed as M 7.0 on its detailed tsunami bulletin . The different magnitude stems from differing measurement methodologies and local network calibrations.
• EMSC (European-Mediterranean Seismological Centre): M 7.7, with a depth of 20 km and location 8.374°S, 121.358°E .

Aftershock Sequence

The USGS recorded at least three significant aftershocks following the mainshock: magnitudes 5.9, 5.6, and 6.1 . A magnitude 5.0 aftershock was also detected on the same day . No evidence was found in the available sources for a magnitude 6.2–6.3 aftershock exactly 15 minutes after the mainshock; the available aftershock magnitudes and timing do not match that specific claim.

Tsunami Warning and Evacuation Orders

BMKG issued an early tsunami warning immediately after the earthquake, with initial coverage for East Nusa Tenggara (NTT), West Nusa Tenggara (NTB), South Sulawesi (Sulsel), and Southeast Sulawesi (Sultra) . The warning was later updated to include specific advisory levels.

Eight districts were placed on "Siaga" (alert) status, meaning a tsunami was expected with wave heights potentially reaching 0.5 to 3 metres . Most of these districts were in NTT, including Manggarai, Ngada, Manggarai Barat, Ende, and Sikka — all on the northern coast of Flores . Other areas, like parts of West Nusa Tenggara, were placed on lower-level "Waspada" (advisory) status .

The BNPB (Indonesia's National Disaster Mitigation Agency) urged residents in coastal areas to evacuate immediately and stay away from shorelines until the warning was lifted . Hundreds of residents in coastal areas evacuated in response to the warning .

Tsunami waves of less than 1 metre were recorded in several areas, and the warning was eventually lifted .

Seismic History of the Flores Region

The 2026 earthquake is not the region's first major seismic event. The Flores Thrust fault has generated deadly earthquakes in the past.

The 1992 Flores Earthquake and Tsunami (12 December 1992): A highly destructive event with a magnitude of M 7.5–7.8 (USGS M 7.5–7.8; BMKG M 6.8) . Its epicenter was near Maumere, east of the 2026 event. It generated a tsunami that reached shore in five minutes . At least 2,200 people were killed or missing (1,490 in Maumere, 700 on Babi Island), with more than 500 injured and approximately 90,000 left homeless . Approximately 90% of buildings in Maumere were destroyed by the earthquake and tsunami . This event remains the deadliest earthquake in the region in modern records.

Impact on Coastal Communities in 2026

As of the latest reports in the available evidence, no detailed casualty or damage figures were yet available for the city of Maumere or other tourist areas specifically. The USGS assessed that "some casualties and damage are possible and the impact should be relatively localized" . Approximately 1.5 million people were exposed to strong (MMI VI) to severe (MMI VIII) shaking . The earthquake was felt strongly for around one minute in regions such as Nagekeo and Bima, but initial reports indicated no widespread structural damage .