More than failed tsunami warning systems, earthquake experts condemn a lack of public understanding of the risk as a fatal contributor to the more than 1,400 deaths in a 7.5-magnitude earthquake and tsunami that hit Palu Bay in Sulawesi, Indonesia, on Sept. 29.
“When the source of the tsunami is right on your doorstep, warning is a challenge … the earthquake has to be the warning,” says Gerard Fryer, former senior geophysicist at the Pacific Tsunami Warning Center. The source of the quake was the Palu-Koro strike-slip fault near the island of Sulawesi.
Fryer says Indonesia’s tsunami warning systems failed for various reasons. The most egregious was that its 22-buoy warning network—including two $400,000 buoys donated by the United Nations after a 2004 tsunami hit the islands—has been inoperable since 2012. A warning was issued based on seismographic modeling but was stymied when communication towers were knocked out by the quake.
“If they issued a warning or not, it didn’t get to the people,” says Fryer, but adds that the greatest failing was that the public was not educated about the hazard. “This quake was very severe. Everyone felt it. They have a history of tsunamis at that location, so that should have told them, ‘Let’s get out of here.’ From the casualty stats, it appears not very many of them did.”
Lori Dengler, professor of geology at Humboldt State University, concurs. “Lives were lost because people did not respond to the shaking,” she says, adding that it was also an eye-opener for experts. “This is a really important earthquake and tsunami because the setting is not unlike the San Andreas fault zone in California and a similar fault near New Zealand,” says Dengler. “We don’t think strike slip faults—where the ground is moving horizontally—tend to produce significant tsunamis. But this one did.”
Distinguishing between tsunami and earthquake deaths will be difficult, says Ian Robertson, professor of civil and environmental engineering at the University of Hawaii at Manoa. “The tsunami is estimated at 15 feet or higher, but we’ll learn more when we measure the inundation heights,” he says. Experts await the end of rescue operations to access the site.
“Even if the wave height is 20 feet, that shouldn’t damage an engineered, reinforced concrete structure like the Roa Roa Hotel, which collapsed,” says Robertson. He says timber-frame and steel-frame structures don’t resist the water loads of such a wave, but do resist seismic loads, whereas reinforced concrete structures are the opposite.
“The eight-story Roa Roa Hotel collapse is definitely seismic related,” says Robertson, who adds it’s possible the soil liquefied beneath the building. “That whole town [of Pelu Bay] is on alluvial deposits from the rivers running to the sea and the amplification of the ground shaking can be significant.”