Indonesian tsunami sensors missed huge waves, official says

Indonesian tsunami sensors missed huge waves, official says

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September 30, 2018 00:54:15

Indonesia’s geophysics agency has defended lifting a tsunami warning 34 minutes after it was first issued, following a major earthquake that sent huge waves crashing into the north-eastern coast of Sulawesi island, killing hundreds and leaving thousands more homeless.

The 7.5 magnitude quake and tsunami, which hit the city of Palu, killed at least 384 people, and officials said on Saturday that figure was likely to rise.

The geophysics agency (BMKG) faced criticism on Saturday on social media, with many questioning if the tsunami warning was lifted too soon.

The agency said it followed standard operating procedure and made the call to “end” the warning based on data available from the closest tidal sensor, around 200 kilometres from Palu.

“We have no observation data at Palu. So we had to use the data we had and make a call based on that,” Rahmat Triyono, head of the earthquakes and tsunami centre at BMKG, said.

He said the closest tide gauge, which measures changes in sea level, only recorded an “insignificant”, six-centimetre wave and did not account for the giant waves near Palu.

“If we had a tide gauge or proper data in Palu, of course it would have been better. This is something we must evaluate for the future,” Mr Triyono said.

It was not clear whether the tsunami, which officials say hammered Palu and the surrounding area at extremely high speeds measuring in the hundreds of kilometres per hour, occurred before or after the warning had been lifted.

“Based on the videos circulating on social media, we estimate the tsunami happened before the warning officially ended,” Mr Triyono said.

Underground landslide may have caused tsunami

Baptiste Gombert, a geophysics researcher at University of Oxford, said it was “surprising” the quake generated a tsunami.

Friday’s quake was recorded as a “strike-slip” event where neighbouring tectonic plates move horizontally against each other, rather than vertically, which is what usually generates a tsunami.

“There is some speculation that there was a landslide under the sea which displaced a lot of water and caused the tsunami,” he said, adding the narrow bay on which Palu sits may have concentrated the force of the waves as they moved toward the shore.

Sutopo Purwo Nugroho, spokesman for the disaster agency, told reporters his team had been “preparing to send public warnings that were easy to understand” when the tsunami warning was “suddenly ended”.

The communications ministry said repeated warnings were sent out to residents via text message, but Mr Nugroho said the quake had brought down the area’s power and communications lines and there were no sirens along the coast.

Indonesians took to social media to question the BMKG’s move to lift the tsunami warning and a failure to release information in a timely manner.

“So upset … the warning was lifted … although a tsunami happened,” Twitter user @zanoguccy wrote in a direct message to BMKG.









First posted

September 30, 2018 00:52:45

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