A magnitude 7.2 earthquake struck 38 kilometres (24 miles) south-west of Hengchun at 06:41 on Tuesday, sending a tsunami warning across Taiwan’s southern coast. Authorities told residents in low-lying parts of Pingtung and Kaohsiung counties to move inland before waves expected from 07:20; officials said the first forecast put the largest waves at 1.5 metres (4.9 feet).
But an audit delivered to the government at dawn found that the warning system’s standard scenarios had omitted a shallow section of the offshore fault, leaving officials blind to a more dangerous kind of rupture. A fresh calculation using the quake’s early seismic readings put possible run-up at 4.6 metres (15 feet) in some bays and estuaries, the audit’s lead scientist said.
The fault segment left out
The Coastal Signal Review Office examined 14 tsunami scenarios used by the Taiwan Quake and Tide Service. Nine stopped the modelled rupture before it reached the shallow shelf, according to the audit, which traced the cutoff to a template carried over in the service’s forecasting software. The missing section lies off the Hengchun Peninsula, where a large thrust earthquake can push the seabed upwards and displace water.
Elise Nieminen, a marine seismologist who reviewed the audit, said the quake’s preliminary signals were consistent with rupture extending into the omitted zone. “The first number was calculated with a fault that ends too soon,” she said. “If the rupture ran through the shallow patch, the water can pile up sharply inside the inlets.” She cautioned that the 4.6-metre estimate was a high-end scenario, not a precise forecast.
The service’s deputy director, Alan Koen, urged people not to treat that maximum as the expected wave. He said the agency’s live gauges supported a lower range and that the audit’s scenarios were designed to test extremes. Nieminen countered that the gauges had not yet captured the full wave train and that an early low reading could not rule out a larger surge.
Evacuations before first waves
Emergency officials ordered about 126,000 people from coastal districts to higher ground, opening schools and sports halls as temporary shelters. Traffic slowed on roads leading inland from Donggang and Fangliao, while local authorities used phone alerts and loudspeakers to direct residents away from river mouths. Taiwan’s southern shore is densely settled, and low coastal plains leave little time to move once water enters.
By 07:10, two offshore pressure sensors had registered a change in water level, according to the service’s public data feed, but officials said the readings were not yet enough to confirm the worst-case projection. Herbjörg Mars, an emergency planner in Pingtung County, said shelter staff were preparing for several hours of uncertainty. “We are telling people to stay uphill until the warning is lifted, not to return after one quiet wave,” she said.
The audit also found that the service had not run a full exercise using the omitted fault geometry since 2018. The government said it would revise its scenarios and publish a technical review after the warning ends. For now, scientists say the earthquake’s final rupture map and measurements from the next waves will decide whether the coast faces a brief surge or the much larger flooding shown in the audit’s most severe calculations.
