BMKG: NTT Aftershocks Expected to Decline

RRI.CO.ID, Jakarta - The Indonesian Meteorology, Climatology and Geophysics Agency (BMKG) recorded 4,258 aftershocks following the magnitude 7.7 East Nusa Tenggara (NTT) earthquake as Friday morning, August 21, 2026. BMKG said aftershocks could continue for three to four weeks, although their magnitudes are expected to gradually decrease.

The agency’s Technical Policy Reviewer for Geophysics Admiral Musa Julius told RRI Voice of Indonesia on Friday, August 21, aftershocks are a natural sequence following major earthquakes. He said the earthquake which hit NTT on Saturday, August 15, represents a main shock followed by aftershocks, rather than foreshocks preceding another major earthquake.

Julius said the 7.7-magnitude earthquake was powerful enough to trigger subsequent earthquakes 99measuring magnitudes five and six. He explained that aftershocks of magnitude six could occur during the first week, while magnitude-five events may continue afterward.

According to Julius, after three weeks, aftershocks are expected to decline toward magnitudes four, three, two, and eventually one. However, he noted earthquake fault systems differ, citing Lombok's 2018 earthquake, whose aftershocks continued for approximately two months afterward.

Julius said the Flores sequence could last longer because its 7.7-magnitude earthquake exceeded Lombok's 7-magnitude event. He urged residents to remain outside vulnerable buildings, particularly while authorities assess structures damaged by the initial earthquake.

People should also remain alert for rockfalls and landslides, especially along coastal roads where unstable sediments can amplify shaking. Julius warned previous shaking may have cracked rocks on hillsides, allowing subsequent aftershocks to trigger dangerous landslides.

Such landslides could reach coastal settlements and houses, while falling rocks could obstruct humanitarian assistance and emergency routes. Authorities continue monitoring the aftershock sequence while evacuation posts provide safer temporary locations for residents during the earthquake aftermath.