The government should ensure earthquake and tsunami early warning systems are in good working order and mitigation plans are easily accessible given imminent disaster threats along Sumatra’s western coastal areas, an expert says.
Indonesian Institute of Sciences (LIPI) quake expert Danny Hilman Natawidjaya said the quake-triggered tsunami, which devastated Mentawai Islands regency in West Sumatra on Monday night, was part of a chain process that included the 8.4-magnitude quake that hit the province in September 2007, and was located along the same fault line that caused the catastrophic quake off Aceh in 2004.
The Mentawai tsunami was triggered by a 7.2-magnitude quake that claimed some 400 lives, he said, adding that hundreds of others were still missing. The tsunami occurred 40 minutes after the quake, and was produced by a new equilibrium from the subduction zone of the Indo-Australia and Eurasian plates, which shift at around 60 millimeters a year, he said.
However, Danny warned of the potential of a megathrust at a strength of up to 9.0-magnitude on the Richter Scale is possible because of an accumulation of energy beneath the Mentawai Islands.
“The recent quake was [a result of] the same subduction zone mechanism as the Aceh and Nias quakes. The potential of a massive quake still exists despite the smaller aftershocks,” Danny told reporters in Bandung, West Java on Friday.
Danny is one of the geotechnology scientists at LIPI, working together with the Tectonic Observatory of the California Institute of Technology, who have been conducting research in Sumatra since 1991.
LIPI has also worked together with the Earth Observatory of Singapore (EOS) and Singapore’s Nanyang Technological University to install the Sumatran GPS Array (SuGAR) network along the coast of West Sumatra, one of the most quake-prone areas in Indonesia.
The government began paying more serious attention to perpetual tectonic deformation movements in Sumatra after a massive quake triggered the tsunami that devastated Aceh in 2004, which was followed by the quakes in Nias and Simeuleu Islands and again in West Sumatra last year. The Mentawai Islands chain is located in the volatile area where the Indo-Australia and Eurasian tectonic plates thrust into each other, he said.
The process of energy accumulation from quakes in Sumatra indicated that the Mentawai and Batu islands have subsided by up to 10 millimeters annually. In 2002, Danny and his team installed six GPS devices in Mentawai. Coral recordings showed the pressure from the shifting fault line had entered the final phase prior to a megathrust.
“In the aftermath of the Monday’s quake, I estimate the west coast of Pagai Island has subsided by tens of centimeters,” said Danny, who will leave for Mentawai next week to examine the latest conditions in the area.
The latest tsunami could serve as a lesson for the government to improve the standard operation procedures of a tsunami early warning system, he said.
“Currently, every time a 4.5-magnitude quake takes place offshore, authorities issue a tsunami warning, and this bores people who now regard it as usual. Don’t just rely on an automatic system. If a quake has reached a 7.8 scale, relay a tsunami warning to the local administration immediately. Don’t use text messages that may not be received or read,” Danny said.
The tsunami early warning system, developed by the Meteorology, Climatology and Geophysics Agency over the past three years, still had many flaws — not only in terms of detection devices which only rely on a seismometer without a tsunami buoy, but also was not designed according to the different nature of a quake and tsunami in a respective area, he said.
“We have never conducted a serious evaluation on a national scale or held formal discussions with experts on the weaknesses,” Danny said.
