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| Indonesia earthquake and tsunami: How warning system failed the victims | Indonesia earthquake and tsunami: How warning system failed the victims |
| (35 minutes later) | |
| Hundreds of people have been killed and many still remain missing after a tsunami struck the Indonesian island of Sulawesi on Friday, triggered by a powerful earthquake. | Hundreds of people have been killed and many still remain missing after a tsunami struck the Indonesian island of Sulawesi on Friday, triggered by a powerful earthquake. |
| A tsunami warning was sent out - lasting just over 30 minutes - but it appears to have drastically underestimated the scale of the tsunami that would follow. So what went wrong? | A tsunami warning was sent out - lasting just over 30 minutes - but it appears to have drastically underestimated the scale of the tsunami that would follow. So what went wrong? |
| What actually happened? | What actually happened? |
| A 7.5 magnitude earthquake occurred just off the island of Sulawesi at 18:03 local time (10:03 GMT) on Friday, triggering dozens of aftershocks. | A 7.5 magnitude earthquake occurred just off the island of Sulawesi at 18:03 local time (10:03 GMT) on Friday, triggering dozens of aftershocks. |
| Indonesia's meteorological and geophysics agency BMKG issued a tsunami warning just after the initial quake, warning of potential waves of 0.5 to three metres. | Indonesia's meteorological and geophysics agency BMKG issued a tsunami warning just after the initial quake, warning of potential waves of 0.5 to three metres. |
| But it lifted the warning just over 30 minutes later. | But it lifted the warning just over 30 minutes later. |
| Palu - a city in Sulawesi located in a narrow bay - was hit by waves as high as six metres. The surging water brought buildings down and caused widespread destruction. Hundreds of people had gathered for a beachfront festival and it was was a scene of horror as waves powered over the beach - sweeping up everything in their path. | Palu - a city in Sulawesi located in a narrow bay - was hit by waves as high as six metres. The surging water brought buildings down and caused widespread destruction. Hundreds of people had gathered for a beachfront festival and it was was a scene of horror as waves powered over the beach - sweeping up everything in their path. |
| Indonesia's National Disaster and Mitigation Agency has said that most of the victims in Palu were killed as a result of the tsunami. | Indonesia's National Disaster and Mitigation Agency has said that most of the victims in Palu were killed as a result of the tsunami. |
| Were people aware there was a tsunami? | Were people aware there was a tsunami? |
| Many critics have accused BMKG of lifting the warning too early, though the agency says the waves hit while the warning was still in force. | Many critics have accused BMKG of lifting the warning too early, though the agency says the waves hit while the warning was still in force. |
| BMKG chairwoman Dwikorita Karnawati told the Jakarta Post that the decision to end the warning was made after the agency received information about the tsunami, including a field observation made by a BMKG employee in Palu. | BMKG chairwoman Dwikorita Karnawati told the Jakarta Post that the decision to end the warning was made after the agency received information about the tsunami, including a field observation made by a BMKG employee in Palu. |
| She added that the tsunami alert ended at 18:37, minutes after the third and last wave hit land. She also said that there were no more tsunami waves after the alert ended. | She added that the tsunami alert ended at 18:37, minutes after the third and last wave hit land. She also said that there were no more tsunami waves after the alert ended. |
| But there's a bigger problem - though the alert was sent out, and according to the communications ministry, repeated tsunami warnings were sent to residents via text message - they might not have been received. | But there's a bigger problem - though the alert was sent out, and according to the communications ministry, repeated tsunami warnings were sent to residents via text message - they might not have been received. |
| A spokesman for the disaster agency said the quake had brought down the area's power and communications lines and that there were no sirens along the coast - which might have rendered the alerts essentially useless. | A spokesman for the disaster agency said the quake had brought down the area's power and communications lines and that there were no sirens along the coast - which might have rendered the alerts essentially useless. |
| One video which has been widely shared on social media illustrates the chilling consequences. It shows a man shouting cries of warning towards people alongside the beach, who remain oblivious to a huge approaching wave. | One video which has been widely shared on social media illustrates the chilling consequences. It shows a man shouting cries of warning towards people alongside the beach, who remain oblivious to a huge approaching wave. |
| Does Indonesia have a tsunami early warning system? | Does Indonesia have a tsunami early warning system? |
| Yes. Indonesia's tsunami early warning system is currently made up of a network of 170 seismic broadband stations, 238 accelerometer stations and 137 tidal gauges. | Yes. Indonesia's tsunami early warning system is currently made up of a network of 170 seismic broadband stations, 238 accelerometer stations and 137 tidal gauges. |
| But according to BMKG's head of earthquake and tsunami centre, the current system in place is "very limited". | But according to BMKG's head of earthquake and tsunami centre, the current system in place is "very limited". |
| "Our [current] tools are very lacking," said Rahmat Triyono, speaking to BBC Indonesian. | "Our [current] tools are very lacking," said Rahmat Triyono, speaking to BBC Indonesian. |
| "In fact, of the 170 earthquake sensors we have, we only have a maintenance budget for 70 sensors." | "In fact, of the 170 earthquake sensors we have, we only have a maintenance budget for 70 sensors." |
| However we do know that the system did in fact pick up the tsunami - because a warning was sent out - but what it failed to do was accurately gauge the scale of the tsunami. | However we do know that the system did in fact pick up the tsunami - because a warning was sent out - but what it failed to do was accurately gauge the scale of the tsunami. |
| BMKG revealed that the nearest closest tidal gauge to Palu was one that was well over 200km away. | |
| The tidal gauge, which measures changes in sea level, only recorded an "insignificant" 6cm (2.5in) rise. The tsunami height was estimated to be less than 0.5m, BMKG said (in Indonesian). | |
| "We have no observation data at Palu. So we had to use the data we had and make a call based on that," Mr Triyono told Reuters. | "We have no observation data at Palu. So we had to use the data we had and make a call based on that," Mr Triyono told Reuters. |
| "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." | "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." |
| Could more lives have been saved? | Could more lives have been saved? |
| It's possible, as Indonesia does actually have a more advanced tsunami warning system, including a network of 21 buoys connected to seafloor sensors which would have transmitted advance warnings. | |
| However none of these buoys - donated by the US, Germany and Malaysia after the devastating 2004 Indian Ocean tsunami that killed nearly a quarter of a million people - are working. Some have been damaged by vandals and others have been stolen. | |
| A replacement system has been delayed due to a lack of funds. | |
| Because of this the BMKG predicts post-earthquake tsunamis using a modelling system based on the earthquake depth and magnitude. | Because of this the BMKG predicts post-earthquake tsunamis using a modelling system based on the earthquake depth and magnitude. |
| If data were available from the buoys, "then our tsunami warning level would be more accurate", Mr Triyono told BBC Indonesian. | |
| The latest disaster has highlighted the costs of Indonesia not having implemented a more sophisticated early warning system. | The latest disaster has highlighted the costs of Indonesia not having implemented a more sophisticated early warning system. |
| BPPT, the agency which manages the buoy system, has previously acknowledged that government efforts have mostly focused on post-earthquake relief, while paying "minimal" attention to pre-disaster anticipation. | BPPT, the agency which manages the buoy system, has previously acknowledged that government efforts have mostly focused on post-earthquake relief, while paying "minimal" attention to pre-disaster anticipation. |
| But was the tsunami expected? | But was the tsunami expected? |
| Not exactly. | Not exactly. |
| This is not the kind of earthquake that typically generates a major tsunami, according to Prof Philip Li-fan Liu, vice-president of the department of civil and environmental engineering at the National University of Singapore. | This is not the kind of earthquake that typically generates a major tsunami, according to Prof Philip Li-fan Liu, vice-president of the department of civil and environmental engineering at the National University of Singapore. |
| Tsunamis are typically only generated when there is a large vertical displacement, he said. But in this case, the tectonic plates were "rubbing against each other horizontally, and when [that] ruptures it only creates a significant horizontal movement and not much of a vertical movement". | Tsunamis are typically only generated when there is a large vertical displacement, he said. But in this case, the tectonic plates were "rubbing against each other horizontally, and when [that] ruptures it only creates a significant horizontal movement and not much of a vertical movement". |
| Why such massive waves were unleashed on Palu could perhaps be explained by the nature of the bay itself. | |
| According to Dr Hamza Latief, an oceanographer at the Bandung Institute of Technology, Palu has witnessed tsunamis in the past and when a tsunami hits its narrow and elongated bay its impact is amplified. |