M5.1 Offshore Quake Reported in Flores Sea as Manggarai Aftershocks Continue

Labuan Bajo — A magnitude 5.1 earthquake was reported in the Flores Sea on the night of Saturday, 19 September 2026, with its epicentre described as around 67 kilometres northeast of Ruteng, East Nusa Tenggara, according to EarthquakeList.org. The event was characterised as shallow, with a reported depth of about 10 kilometres beneath the seabed.

EarthquakeList.org listed the origin time as 21:56 local time (Makassar Time), equivalent to 13:56 UTC. The site’s event summary placed the epicentre in the Flores Sea, just offshore from northern Manggarai, and noted that the shaking was detected by 74 stations in the monitoring network. The report classified the tsunami risk from this offshore shock as low.

As of Sunday, Indonesian outlets were reporting smaller earthquakes in Manggarai on the same date, based on information from the Meteorology, Climatology and Geophysics Agency (BMKG). One widely cited BMKG bulletin described a magnitude 4.0 earthquake at 11:11 WITA on 19 September, with an epicentre 78 kilometres north of Ruteng at a depth of 4 kilometres.

Another BMKG update, carried by local media, reported a magnitude 3.4 event at 21:45 WITA, 85 kilometres northeast of Ruteng at a depth of 25 kilometres. These BMKG bulletins did not refer to a magnitude 5.1 earthquake on that date.

Reported offshore tremor and local shaking

According to EarthquakeList.org, the 5.1 earthquake occurred under the Flores Sea, roughly 12 miles offshore from northern Flores. The site gave epicentral coordinates of about 8.10 degrees south and 120.88 degrees east, and described the shock as part of an ongoing sequence following a major Flores earthquake in mid‑August 2026. The monitoring summary indicated that several smaller earthquakes were recorded in the hours after the 5.1 event, including a magnitude 3.6 shock roughly seven hours later.

Local and national media in Indonesia have focused on a series of smaller but felt earthquakes in the Manggarai area that weekend. A report based on BMKG analysis stated that a magnitude 4.7 earthquake struck at 20:20:30 WITA on Friday, 18 September, with an epicentre offshore about 46 kilometres north of Ruteng at a depth of 8 kilometres. BMKG located that event at 8.20° south and 120.50° east and confirmed that it did not generate a tsunami.

BMKG officials quoted in Indonesian coverage explained that the 18 September magnitude 4.7 earthquake was linked to movement on the Flores back‑arc thrust and formed part of the aftershock sequence following a magnitude 7.7 mainshock that struck Flores on 15 August 2026. Shaking from the 4.7 event was reported at intensity III–IV on the Modified Mercalli scale in parts of Manggarai, and II in some neighbouring areas, meaning it was felt by residents but generally did not cause structural damage.

Prolonged aftershocks in Manggarai and surrounding seas

Indonesian data and media reports indicate that the region has experienced thousands of aftershocks since the August mainshock, including multiple events strong enough to be felt in Ruteng, Manggarai and West Manggarai. BMKG summaries cited by data services describe several earthquakes in northern Flores on 18 September with magnitudes between 4.1 and 4.7, at shallow depths of 3–8 kilometres and epicentres 46–54 kilometres north of Ruteng.

For residents and travellers in Manggarai and coastal centres such as Labuan Bajo, BMKG has urged people to remain calm but vigilant and to pay attention to official information channels for any updates on seismic activity. Earthquake guidance from BMKG and local authorities generally advises avoiding buildings with visible structural damage and being cautious around steep slopes or areas prone to landslides after strong or repeated shaking.

Marine‑tourism and transport operators in the Flores Sea are advised to monitor BMKG bulletins and harbour‑master notices when significant earthquakes occur offshore, particularly in the context of a prolonged aftershock sequence. While both EarthquakeList.org and BMKG assessments for the mid‑September events indicate low tsunami potential, official advisories remain the primary reference for any changes to navigation, port operations or coastal safety measures.

Key reported parameters

• Time (EarthquakeList.org): 21:56 local time (Makassar Time), Saturday, 19 September 2026.
• Reported magnitude: 5.1, offshore Flores Sea.
• Reported depth: about 10 kilometres.
• Reported location: approximately 67 kilometres northeast of Ruteng, in the Flores Sea, about 12 miles offshore.
• Detection: 74 stations recorded the event, according to EarthquakeList.org.

Sources

• EarthquakeList.org – Shallow M5.1 Earthquake hit in the Flores Sea near Ruteng (Indonesia) on Saturday Evening
• POS-KUPANG.COM – Gempa Magnitudo 4,7 Guncang Flores, Dirasakan di Manggarai hingga Manggarai Barat
• Databoks Katadata – Gempa Terkini 4,7 M Guncang Ruteng, Manggarai, Ini Penjelasan BMKG