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The magnitude 7.5 earthquake struck Sulawesi Island on Friday, causing waves three meters high on part of its northwest coast, resulting in groups of people captured on the coast, apparently unaware of the danger.
Online criticism from Indonesians focused on allegations that the country's meteorological and geophysical agency (BMKG) canceled the tsunami warning too early.
The alert was triggered shortly after 18 hours. Friday, warning potential waves up to three meters. The warning was canceled at 6:36 pm However, the agency said the alert was only lifted after the tsunami.
In a statement, the head of the organization, Dwikorita Karnawati, called the allegations "incorrect".
"Our work is based on the computer system / artificial intelligence.The alert system was lifted with the approval of 28 other countries in the Indian Ocean," said Karnawati.
Phil Cummins, professor of natural hazards at Australian National University, told CNN that if all the facts had not yet been revealed, he doubted that the problem of warning signs was a major concern.
"At the time a warning was potentially useful, it was apparently in force, and it seems much more important to me than having canceled it prematurely after the tsunami," he added.
Did the tide buoys work?
The questions focused on the Indonesian warning system, based on a grid of 134 tide gauge and earth seismograph stations, reinforced by educational campaigns to train people to respond to the tsunami.
His warnings are transmitted by sirens and text messages.
"According to information I've heard in the media, the sirens were not working because the earthquake had cut off the power," Cummins said. "If that's true, it's something that really should be examined."
CNN has not been able to confirm this information.
The experts also examined the number of tide gauge systems used to measure sea level on the coast.
"134 tide gauge stations can not confirm the tsunami generation for the country that has perhaps the largest number of islands in the world," said Professor Costas Synolakis, director of the center of alert to tsunamis from the University of Southern California.
"To be effective, you need to have a tide gauge near each coastal community," he added.
Sutopo Purwo Nugroho, spokesman for the country's National Disaster Agency (BNPB), admitted that no more than 22 deep-sea buoys connected to ocean bottom sensors to monitor offshore tsunamis Indonesian had been running for six years.
Shape of the amplified waves of the bay
International experts said that while Indonesia's warning system could be improved, its geographical position and the nature of the disaster made tsunamis virtually impossible to defend.
"First and foremost, we must understand that each tsunami is unique and therefore very difficult to predict, especially where there are no long periods between the earthquake and the tsunami," said Charitha Pattiaratchi. , professor of oceanography at the University of Western Australia.
He added that the epicenter of the earthquake was on the ground, as was a very low probability of generating a tsunami, suggesting that it could have been triggered not by the earthquake, but by an underwater landslide.
Pattiaratchi said that Palu, the largest city affected by the tsunami, is at the head of a long, narrow bay 30 to 40 km in length. "As the tsunami traveled this bay, it would have become very amplified."
Adam Switzer, tsunami expert at the Observatory of the Earth in Singapore, said that the main Indonesian warning system – a database model using different scenarios based on the first parameters of the earthquake – "seems have worked ".
The seismic sequence was complicated, he added, with multiple aftershocks and a very high probability of one or more landslides above or below the surface of the ocean.
"This is a very unusual event and satellite imagery and eyewitness videos show a number of unusual features that will take months to resolve," Switzer said.
"I do not know of any tsunami warning system that can handle multiple shocks or landslides because it is too physically and informally complicated for current technology," he said.
In addition, in the case of Indonesia, its buoys and gauges are mainly placed in areas considered more likely targets for tsunamis, which Sulawesi was not, said Pattiaratchi.
"This is not a region where significant tsunamigenic earthquakes have occurred in the past," he added.
"With limited funds, everyone needs to make decisions to prioritize, so if there was no reason – based on historical events – then decisions are made."
