The Mw 7.7 earthquake that struck northern Flores, East Nusa\nTenggara, on 15 August 2026, around 30 kilometres northeast of Mbay,\nNagekeo, at a depth of about 15 kilometres, caused widespread damage and\ndozens of fatalities. A tsunami early warning was issued and later\nlifted after monitoring showed a relatively small tsunami.<\/p>\n
The event immediately recalled the Flores earthquake of 12 December\n1992. Its magnitude was almost the same, around Mw 7.7\u20137.8, but the\naccompanying tsunami was highly destructive. At Riangkroko, on the\nnortheastern tip of Flores, a run-up of up to 26.2 metres was recorded\nand thousands of lives were lost, said Widjo Kongko, a researcher at the\nHydrodynamics Technology Research Centre of the National Research and\nInnovation Agency (BRIN), in a written statement on Tuesday\n(24\/8\/2026).<\/p>\n
According to Widjo, the two earthquakes had nearly identical\nmagnitudes but produced very different tsunamis. The key lies not only\nin the size of the earthquake but in how the seafloor moves when a fault\nruptures. A tsunami occurs when seafloor displacement disturbs the water\ncolumn above it. Therefore, the source location, fault mechanism,\ndirection and magnitude of slip, depth, and the shape of the seafloor\nand coastline all help determine the size of the tsunami.<\/p>\n
Flores lies on the Flores Back-Arc Thrust system, an active tectonic\nzone resulting from the interaction of the Australian and Eurasian\nplates. The 1992 earthquake occurred very close to the coast and\nproduced seafloor deformation that effectively generated a tsunami.<\/p>\n
However, there is one interesting point. A tsunami model using only\nfault-induced deformation can explain many observations but cannot\nreproduce the extreme 26.2-metre run-up at Riangkroko. This is where the\nhypothesis of an earthquake-triggered submarine landslide becomes\nimportant. Previous research has indicated landslides at several\nlocations and shown that the combination of tectonic deformation,\nlandslides, and steep bathymetry can locally amplify a tsunami. Thus,\nthe 26.2-metre figure at Riangkroko should not be regarded solely as a\ndirect result of the earthquake magnitude.<\/p>\n
What about 2026? Although the magnitude again reached Mw 7.7, initial\nmodelling shows that the resulting tsunami was relatively small. The\nearthquake source modelling used a finite-fault model from the United\nStates Geological Survey (USGS), which describes the earthquake source\nand fault plane in greater detail. Tsunami wave propagation was then\nmodelled using the TUN3-BRIN model to see how the tsunami travelled from\nthe source towards coastal areas. However, at several locations the\nobserved tsunami height was still greater than the simulation\nresults.<\/p>\n
This difference is worth further investigation, especially once\nearthquake source data, bathymetry, and sea-level records become more\ncomplete. Care is needed when comparing the tsunami figures from the two\nevents. The 26.2 metres in 1992 was a run-up measured on land, whereas\nthe roughly 1.6 metres in 2026 was a tsunami height measured at a\nmonitoring location. The two are not exactly the same quantity.\nNevertheless, the difference still shows that the tsunami responses of\nthe two events were indeed very different.<\/p>\n
Widjo stressed that the most important lesson from Flores is not that\nthe tsunami threat has diminished. On the contrary, the 2026 earthquake\nagain showed that the Flores Back-Arc Thrust system remains active and\ncapable of producing large earthquakes. The 1992 history also shows that\na local tsunami can reach the coast within just a few minutes. In such\nconditions, coastal communities do not have much time to wait.<\/p>\n
Therefore, after feeling a strong earthquake or prolonged shaking in\na coastal area, the safest action is to move away from the shore\nimmediately and head to higher ground without waiting for a siren. The\n1992 and 2026 Flores earthquakes offer a simple but important lesson:\nnearly identical magnitudes do not mean the tsunami threat is the same.\nWhat matters is how the earthquake moves the seafloor, how the waves\npropagate, and how the coast responds. Understanding these processes is\nan important part of efforts to reduce disaster risk in East Nusa\nTenggara.<\/p>", "url": "https:\/\/jawawa.id\/newsitem\/why-the-1992-flores-earthquake-was-deadlier-than-2026-1787633469", "image": "" }, "sponsor": "Okusi Associates", "sponsor_url": "https:\/\/okusiassociates.com" }