August 21, 2026 | 11:11 am
TEMPO.CO, Jakarta - The Meteorology, Climatology, and Geophysics Agency (BMKG) recorded 4,258 aftershocks following the magnitude 7.7 earthquake in Flores, East Nusa Tenggara (NTT), as of Friday, August 21, 2026, at 5:00 a.m. local time. Of the total aftershocks, residents directly felt 118 tremors, 31 of which registered magnitudes above 5.0.
BMKG Earthquake and Tsunami Center Director Wijayanto predicted that this sequence of aftershocks will persist for the next three to four weeks. He noted that the initial phase of the aftershock sequence continues to exhibit a complex temporal pattern that has yet to stabilize.
"Aftershock activity in the first few days is relatively high and has not shown a significant pattern of decay. Daily seismic occurrences reached 704 on the first day, rose to 746 on the second day, hovered between 668, 649, and 627 from the third to fifth days, before climbing again to 802 on the sixth day," Wijayanto said in a statement on Friday, August 21, 2026.
According to BMKG monitoring, the aftershock sequence has produced several significant tremors with perceived intensities of IV–VI MMI, which were strongly felt by local residents. The agency noted that notable tremors occurred on August 19, 2026, at 11:17 p.m. with a magnitude of 5.6, and on August 20, 2026, at 5:45 a.m. with a magnitude of 5.8.
Another significant shock struck on August 20, 2026, at 9:47 a.m. with a magnitude of 5.8, triggering secondary damage to already affected buildings and bridges, as well as inducing landslides in several locations.
According to Wijayanto, seismic relocation data indicates that the aftershocks are not distributed evenly, but have instead formed several distinct clusters. The main cluster surrounds the source zone of the magnitude 7.7 earthquake north of Nagekeo, extending along the Flores Back-Arc Thrust. Meanwhile, secondary aftershock clusters emerged west of the primary source zone, specifically north of Manggarai Regency.
Daily seismic data reveals a dynamic shift in focus over time. From the first to the fourth day following the mainshock, earthquakes were distributed across all clusters from east to west. However, on the fifth and sixth days, seismic activity shifted and concentrated in the western clusters, as intensity in the eastern clusters gradually waned.
Wijayanto affirmed that the BMKG continues to operate its real-time monitoring system 24/7 to track every development. Agency officials are continuously analyzing event frequency, magnitude, epicenter distribution, fault movement directions, and focal mechanisms to deliver accurate, timely information to the public and authorities.
Previously, a magnitude 7.7 earthquake struck Flores Island, East Nusa Tenggara, on Saturday, August 15, 2026, at 5:58 a.m. local time. The quake's epicenter was located at sea at a depth of 10 kilometers, roughly 36 kilometers northeast of Mbay in Nagekeo Regency.
Read: Pope Leo Says 'Deeply Saddened' by NTT Earthquake
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