Tsunami warning systems were of little use in Palu, say experts

LOS ANGELES: Across the world, dozens of deepsea ocean sensors are a first line of defence that warns officials when a devastating tsunami is coming.

When an earthquake strikes, the sensors capture the movement of ocean waters, giving authorities time to alert residents to move to higher ground.

But the destructive tsunami that hit Indonesia early on Saturday highlights a critical flaw.

If a big quake strikes too close to shore, it will not be detected by those deepsea sensors, and the wave can arrive before major evacuations occur.

That is what happened on the Indonesian island of Sulawesi, when a magnitude 7.5 earthquake hit just north of a narrow bay, sending waves as tall as 6m straight into Palu, a town where at least 1234 people were killed.

It was only about 10 minutes between the earthquake and the first wave that washed across Palu, California Institute of Technology seismology professor Pablo Ampuero said.

When a quake hits further out in the ocean, officials can have hours to evacuate residents before waves hit.

Compounding matters, when a tsunami warning was issued by the Indonesian Government, the public may not have received the alert, Ampuero said, because the quake knocked out electricity and communications systems.

During the 2011 Japan tsunami, some of the first detailed alerts underestimated the size of the tsunami to be lower than the protective sea walls on the coast. Then the communications were cut off, leaving the public with a false sense of security.

Tsunami science has improved since the 1980s, thanks to a new generation of detection equipment. Nations rallied to fill in gaps in the global network after the 2004 Sumatra tsunami exposed shortfalls, including in the Indian Ocean.

Some news reports after Saturday’s quake initially focused on the state of disrepair of Indonesia’s network of nearly two dozen deepsea sensors as a possible factor in the loss of life. The Germanfunded effort never produced a working system, University of Southern California civil and environmental engineering professor and tsunami expert Costas Synolakis said.

He and others, however, said that even having a working deepsea sensor network of the kind used by the United States and other nations — known as DART — may not have helped. Deepsea sensors are more intended to detect tsunamis that are further from its destination, not a matter of minutes from shore.

Experts say it makes sense for people along the coast to seek higher ground in a major quake.

‘‘If you feel strong ground shaking and it lasts for 10 to 15 seconds or so. . . don’t take any chances. If you’re in a coastal area or along the beach, move uphill and inland as quickly as possible,’’ said Stuart Weinstein, deputy director of Hawaii’s Pacific Tsunami Warning Center.

‘‘The worst case is you take a fast walk for nothing; on the other hand, it could save your life.’’ — TCA