By Andi Jatmiko and Margie Mason
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Many, like Susanti in the devastated village of Petobo, had no idea they were in an area already identified by the government as a high-risk zone for the devastating geological phenomenon that causes soft ground to liquefy during earthquakes.
But Indonesian scientist Gegar Prasetya wasn’t surprised by any of the events that occurred at dusk on Sept. 28, killing nearly 2,000 people and leaving possibly thousands more missing. He had warned people for years that the area around Sulawesi island’s Palu Bay had been struck before and was due for another potential combination of factors to create a perfect storm capable of unleashing earthquakes, landslides, tsunami waves and soil liquefaction.
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But it wasn’t just weak sediment in the ocean that gave way. Wet, sandy soil also separated and came alive through liquefaction in some areas due to the earthquake’s radical vibrations. The ground simply lost its strength and turned to mush beneath people’s feet, creating mud that acted like quicksand. People, houses, cars and streets were swallowed and covered by a thick carpet of what — just seconds earlier — had been solid earth. Fast-moving landslides also were launched above ground, possibly causing even more localized tsunami waves.
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However, the central government did produce a map in 2012 identifying large swaths of Palu, a city of 380,000 people, where liquefaction could occur. The area of Petobo, for instance, was classified as having high-risk potential. The report also recommended that housing and industrial areas should best be built in areas with low liquefaction risk. It suggested mitigation efforts, including building structures with deep foundations anchored into firmer layers of earth.
Good urban planning is ultimately the key to saving lives, said Sri Hidayati, head of earthquake mitigation at the Energy Ministry’s Geology Agency, which produced the report that was shared with the provincial and district governments in Sulawesi. She said it’s her agency’s responsibility to provide the mapping, but it’s up to local authorities to “use it or not.” Calls Monday to Palu’s vice mayor and the mayor’s aid went unanswered.
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