15,722 Aftershocks Recorded in 30 Days After Flores Earthquake

September 15, 2026 | 05:54 pm

TEMPO.CO, Jakarta - Indonesia’s Meteorology, Climatology, and Geophysical Agency (BMKG) recorded 15,722 aftershocks ranging from magnitude 0.9 to 6.2 in the 30 days following the magnitude 7.7 earthquake that struck Flores, East Nusa Tenggara (NTT).

“BMKG has recorded 15,722 aftershocks ranging from magnitude 0.9 to 6.2. Of these, 190 were felt by residents,” BMKG Acting Deputy for Geophysics Ardhasena Sopaheluwakan said at a press conference in Jakarta on Tuesday.

Aftershocks Continue to Decline

Based on its latest monitoring and analysis, BMKG said the daily and weekly frequency of aftershocks in NTT has declined, indicating that the sequence has entered a decay phase.

Ardhasena said the decline is reflected in the number of aftershocks recorded each week. BMKG recorded 5,011 aftershocks in the first week after the main earthquake, followed by 4,267 in the second week, 3,158 in the third week and 2,421 in the fourth week.

By the fifth week, BMKG had recorded 864 aftershocks as of 5 a.m. Jakarta time on September 15, 2026.

Stronger Aftershocks Becoming Less Frequent

BMKG Earthquake and Tsunami Director Wijayanto said 26 aftershocks, or 0.2 percent of the total, had a magnitude of 5.0 or higher.

He said earthquakes in this range could be felt over a wider area and potentially affect vulnerable buildings. However, such earthquakes have become increasingly rare, with none recorded in the past week.

There were also 476 aftershocks measuring magnitude 4.0 to below 5.0, accounting for 3 percent of the total. Their frequency has continued to decline after the fourth to fifth weeks following the main earthquake, Wijayanto said.

Aftershocks measuring magnitude 3.0 to below 4.0 accounted for 3,308 events, or 20.9 percent of the total. These were generally felt only locally and did not cause damage.

Smaller Tremors Could Continue for Months

Wijayanto said the decline in aftershock activity reflects a statistical trend and does not indicate when the sequence will end.

“This estimate reflects a statistical trend in the decay of earthquake activity. It is not an estimate of the exact date when the earthquake sequence will end, nor is it a prediction of when the next earthquake will occur. People are advised to remain alert given NTT’s naturally high level of seismic activity,” he said.

He added that magnitude 3.0 to below 4.0 aftershocks were expected to continue for another six to seven weeks, although their frequency would continue to decline.

Meanwhile, smaller aftershocks below magnitude 3.0 accounted for the majority of the activity, with 11,993 events, or 75.9 percent of the total. Most were detected only by seismographs and were not felt by residents.

BMKG expects aftershocks below magnitude 3.0 to continue for several months.

The magnitude 7.7 mainshock struck NTT on August 15, 2026.

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