2026 East Nusa Tenggara earthquake
Earthquake in Indonesia
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On 15 August 2026, at 05:58 WITA, a Mw 7.7 earthquake struck off the coast of the island of Flores in East Nusa Tenggara, Indonesia.
  Location within Flores  Location within Indonesia | |
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| Magnitude |
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| Depth |
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| Epicenter | 8.310°S 121.352°E |
| Type | Thrust |
| Areas affected | Flores and Sumbawa, Indonesia |
| Max. intensity | MMI VIII (Severe) |
| Peak acceleration | 0.635 g |
| Peak velocity | 46.9 cm (18.5 in)/s |
| Tsunami | 94 cm (37 in) |
| Foreshocks | mb 4.6 on 2 August 2026 |
| Aftershocks | 7+ ≥Mw 5.0, largest mb 6.1 |
| Casualties | 2+ dead, 5+ injured |
Tectonic setting
Indonesia lies on the Pacific Ring of Fire, an area of significant volcanic and tectonic activity. The archipelago is located between the Eurasian, Pacific and Australian tectonic plates.[1] The Flores area in particular contains both strike-slip faults and thrust faults.[2] The Flores backthrust is north of the island arc of Indonesia, and is formed by the subduction of the Indo-Australian plate underneath the Eurasian plate west of Lombok while being formed by the Australian plate and Banda Arc south of Rote Island.[3] It is characterized by intermediate-depth down-dip subduction.[4] It is a part of the larger backthrust of the back-arc region of Indonesia. Earlier marine geophysical studies have suggested that the back-arc backthrust consists of two regions: the Wetar thrust and the Flores thrust. However, newer research suggests that the whole thrust is continuous, spanning a distance of about 2,000 km (1,200 mi).[3] The Sunda and Australian plates converge at a rate of 80 mm (3.1 in) per year, in which the Sunda megathrust takes 70 mm (2.8 in) per year of the movement. The remaining 10 mm (0.39 in) per year rate is accommodated by the Flores back-arc thrust. It runs off the north coast of the Lesser Sunda Islands, in the Banda Sea.[5]
The area is seismically active, with 79 earthquakes larger than Mw6.0 recorded in the area between 1900 and 2022. Eleven of those quakes generated tsunamis.[6] In addition, the area has generated at least six tsunamigenic quakes of ≥Ms 6.5 since 1800.[7] There exists substantial tsunami risk associated with the back-arc thrust of Indonesia.[7] The lesser-studied eastern part of Indonesia has been hit by more tsunamis than the more-studied western part.[8] Despite back-arc thrust tsunamis not being as common as megathrust tsunamis, they can still inflict severe damage. The eastern segment of the Flores thrust ruptured in the 1992 Flores earthquake, while the western segment has remained unruptured.[9]
Earthquake
The earthquake occurred at 05:58 WITA. It measured Mww 7.7 and struck at a depth of 10.0 km (6.2 mi) with an epicenter off the northern coast of East Nusa Tenggara, 68 km (42 mi) north-northwest of Ende. It had a focal mechanism corresponding to shallow thrust faulting on an east-striking fault dipping at a shallow angle to the south. The United States Geological Survey (USGS) estimated that the earthquake had a rupture size of 90 by 45 km (56 by 28 mi).[10]
On 2 August, a mb 4.6 foreshock was recorded. At least seven aftershocks exceeding Mw 5.0 were recorded,[11] the largest measuring mb 6.1.[12]
Fault model
The USGS published a preliminary finite fault rupture model with a dimension of 250 by 40 km (155 by 25 mi) and a duration of about 51 seconds. The fault is oriented east-northeast and dips to the south at 29°. Slip propagated bilaterally but the greatest displacement occurred around the hypocenter and to the west-southwest. There are two zones of high slip; one around the hypocenter offshore, and another beneath East Nusa Tenggara; both zones had a maximum slip of 2.5266 m (8 ft 3.47 in) and 2.6131 m (8 ft 6.88 in), respectively. Slip east-northeast of the hypocenter was moderate and peaked at 1.0985 m (3 ft 7.25 in) offshore, north of Sikka. The hypocenter and west-southwest slip zones propagated to the seafloor while extending to depths of 30 km (19 mi) within the crust.[10]
Ground motion
Seismic observations at Meteorology, Climatology, and Geophysical Agency (BMKG) reported a maximum Modified Mercalli intensity of VIII (Severe) in Manggarai Regency and VII (Very strong) in West Manggarai Regency and Bima Regency. In the epicenter areas of Ngada, Nagekeo and Sikka, and further west in Sumbawa, the intensity was VI (Strong). Intensity V (Moderate) was recorded in Sumba Timor, Flores Timur and III–IV (Weak–Light) in some regencies of southern Sulawesi. A maximum peak ground acceleration of 0.635 g was recorded at Kuwus district in West Manggarai Regency, while a peak velocity of 46.9 cm (18.5 in)/s was recorded by a seismic station at Ruteng.[13]
Tsunami
Indonesia's Meteorology, Climatology, and Geophysical Agency (BMKG) issued a tsunami warning for South Sulawesi, East Nusa Tenggara, and West Nusa Tenggara.[14] Evacuation orders were issued because of the warning. The BMKG later declared these warnings over.[15] The BMKG recorded a tsunami with a maximum height of 0.94 m (3 ft 1 in) at Maurole district in Ende Regency.[16] At Labuan Bajo in East Nusa Tenggara, a 30 cm (12 in) tsunami was recorded.[17]
Impact
Two people were killed and five others were injured in Maumere, where a maritime passenger terminal collapsed, with hundreds of passengers in the terminal being hit by falling debris.[18] Many buildings were damaged in Ruteng, including the Frans Sales Lega Airport where the ceiling partially collapsed.[19][20] Buildings were also damaged in Borong, East Manggarai Regency.[21] In the remote areas of the regency, many homes collapsed and several bridges were damaged. Damage also occurred in a campus building of a university in Ruteng. Many residents fled to hilly areas due to fears of a tsunami.[22] In Mbay, Nagekeo Regency, at least five or six homes were reportedly damaged.[23] In Labuan Bajo, buildings were damaged in several locations, including a hotel.[24] Many homes and buildings were damaged or destroyed in West Manggarai Regency.[20] In Bima, West Nusa Tenggara, several homes and buildings were damaged, including a mosque and a warehouse.[25] Strong shaking was felt in Makassar, where it lasted two minutes.[26]