Indonesia: West Sumatra on tsunami alert

Syofiardi Bachyul Jb and Slamet Susanto, The Jakarta Post 12 Nov 15;

Five years after the deadly Mentawai tsunami, geologists have called on local administrations and residents in West Sumatra to anticipate another possible tsunami following the increasing earthquake intensity on the province’s Siberut Island and the Batu Islands.

Speaking to The Jakarta Post on Wednesday, the Indonesian Geologists Association’s (IAGI) West Sumatra branch head Ade Edward said the earthquake intensity had been increasing for the last three years in the Siberut area and for the last two years in the Batu Islands with magnitudes of between 3 and 4 on the Richter scale.

“On average, the small-scale earthquakes measuring below 5 on the Richter scale have occurred nine times in both locations. The magnitude [of the quakes] has also tended to increase,” Ade said.

The latest earthquake measuring 6 on the Richter scale occurred on Sunday in waters off the Batu Islands. Earlier, another earthquake with a 5.5 magnitude also hit Siberut. “We are afraid the magnitude of the upcoming quakes will increase, releasing a huge amount of energy,” Ade said.

There is no technology available to forecast the emergence of an earthquake.

In 2010, a tsunami triggered by a magnitude 7.2 earthquake struck the Mentawai Islands, located off the western coast of West Sumatra, killing hundreds of people and displacing thousands of others.

Many international geologists have been studying the earthquake potential of Siberut, the largest and northernmost of the Mentawai Islands. The Mentawai megathrust zone in Siberut, for example, reportedly could have an earthquake with a magnitude of up to 8.9. An earthquake with 8.4 magnitude occurred there in the late 18th century.

The latest research as of June 2015 from a number of experts from the US and Singapore from Mentawai Gap-Tsunami Earthquake Risk Assessment (Mega-Tera) concluded that major earthquakes could threaten areas around Mentawai and Siberut in the next 20 years.

The quakes are also believed to have the potential of causing a tsunami that could hit the West Sumatra capital of Padang in 22 minutes.

Nelia Budi, a Padang resident, said that the local administration had not run any tsunami familiarization programs over the past few years.

“In the past, when a quake was felt, we would quickly move away from the beach. Now, many people just laugh in their yards [when a quake occurs],” Nelia said.

Meanwhile, a 5.7 magnitude quake jolted the southern part of Java on Wednesday.

The epicenter, according to the Meteorology, Climatology and Geophysics Agency (BMKG) was located in the Indian Ocean, 120 kilometers southwest of Bantul regency, at a depth of 93 kilometers.

No casualties or damaged buildings were reported.

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