Timeline Peringatan Dini Tsunami Gempabumi Donggala 28 September 2018.#infobmkg #iotictsunami #mitigasibencana #gempatsunami #budayasadarbencana #siapuntukselamat #paludonggala #inatews #BMKG #PrayForDonggala #PrayforSulteng pic.twitter.com/8zDx5kYAtH
— InaTEWS BMKG (@InaTEWS) October 1, 2018
A powerful tsunami caught many by surprise last Friday when it plowed through the northwest coast of Indonesia’s Sulawesi Island. Triggered by a 7.5 magnitude earthquake, at least 844 were confirmed dead by Monday morning. Many of the deaths caused by the tsunami were recorded in the city of Palu, located at the head of a narrow bay, where hundreds had gathered for a beachfront festival.
In the days following the disaster, many Indonesians have blamed the high rate of fatality on the country’s meteorology and geophysics agency (BMKG), claiming that it lifted the tsunami warning prematurely, about 30 minutes after the initial earthquake. The BMKG states that the warning was canceled only after the tsunami had already hit, with the approval of more than two dozen nearby countries.
“Our work is based on computer system/artificial intelligence. The warning system was lifted with the approval of the 28 other countries along the Indian ocean,” BMKG Chairman Dwikorita Karnawati said in a statement.
Although the warning was in effect, perhaps the more important question is whether the alert was actually communicated. Tsunami alerts in Palu are sent out using sirens and text messages. However, a spokesperson from Indonesia’s disaster agency reported that the earlier earthquake had brought down both the power and communications lines.
Further questioning of Indonesia’s tsunami early warning system brought to light just how limited Indonesia’s warning system currently is and the challenge that officials face in maintaining it. Although Indonesia has 170 seismic broadband stations, the head of BKMG’s earthquake and tsunami center reported to BBC Indonesia that “of the 170 earthquake sensors we have, we only have a maintenance budget for 70 sensors.”
Indonesia does have a more advanced detection and warning system consisting of a network of 22 buoys connected to seafloor sensors, donated by the US, Germany, and Malaysia after the deadliest tsunami in recorded history in 2004. According to Sutopo Purwo Nugroho, spokesman for the country’s national disaster agency, none of the additional buoys had worked for the last six years. Some have been damaged by vandals or stolen and a replacement system has yet to be implemented due to insufficient funding.
Having data from the sensors could have made the warning more accurate. Using a modelling system based on earthquake depth and magnitude the BMKG had predicted the height of the tsunami to be less than half a meter (approximately 1.6 feet). When the tsunami struck Palu, the waves were reported to be as high as 5.5 meters (approximately 18 feet). Oceanographers attribute the amplification of the waves to the geography and shape of the bay. As the bay narrows and becomes more shallow, more water is forced up onto shore.
International experts warn that even if the warning system was improved, there still might not have been a way to prevent the tragedy in Palu. The earthquake was complicated by multiple aftershocks and likely created the tsunami due to landslides rather than the vertical displacement of water, as most tsunamis are formed.
“No tsunami warning system I know of can handle multiple shocks or landslides as it is just too physically and computationally complicated for current technology,” Adam Switzer, a tsunami expert at the Earth Observatory of Singapore, told CNN.
The majority of the buoy array is also located away from where this earthquake and tsunami took place, in areas considered more likely to have tsunamis. In remarks made to CNN after the event, University of Western Australia professor of oceanography Charitha Pattiaratchi noted, “With limited funds everyone have to take decisions to make priorities. So if there was no reason — based on historic events — then decisions are made.”
Sources and Further Readings
Tectonic Earthquake Press Release – BMKG Meteorology Climatology and Geophysics Council
Indonesia Tsunami’s Power After Earthquake Surprises Scientists – New York Times