On 28 September 2018 a magnitude 7.5 earthquake struck Central Sulawesi, Indonesia, rupturing the Palu-Koro Fault, a fast-moving strike-slip fault that runs directly through Palu Bay. It followed a smaller magnitude 6.1 foreshock earlier the same day and struck at a shallow depth of about 10 km, close beneath the city of Palu itself.
Minutes after the shaking, a tsunami up to 5-6 metres high surged into the narrow, funnel-shaped Palu Bay — a wave far larger than seismologists initially expected from a strike-slip quake, likely amplified by an underwater landslide. It struck a beachfront crowded with people at a festival, drowning many who had no warning.
The earthquake's most unusual damage came from soil liquefaction: shaking turned water-saturated ground beneath the Petobo and Balaroa neighbourhoods into a churning slurry that swallowed entire city blocks, burying thousands of homes and residents alive in minutes — one of the most severe liquefaction disasters ever documented. Total fatalities from the combined earthquake, tsunami and liquefaction reached about 4,340, with over 10,000 injured and more than 200,000 displaced.
Indonesia's national tsunami warning system had issued and then prematurely cancelled an alert before the wave struck, a failure that prompted a major review of the country's sensor network. Palu remains a reference case for scientists studying how strike-slip earthquakes can still trigger destructive tsunamis, and for engineers studying liquefaction hazard in coastal river-delta cities.