Experts predict major quake in N. Sumatra

Monday, September 04, 2006

Apriadi Gunawan, The Jakarta Post, Medan

Geologists are warning people living along North Sumatra’s western coastal areas that a major earthquake is likely during the next few years.
North Sumatra Indonesian Geologists Society coordinator Jonathan I. Tarigan said fault lines in the area had caused three large earthquakes last century.

He said the tremor would probably be less than 8 points on the Richter scale but still be deadly.

“The quake is likely to be from 6 to 7 on the scale”, a high enough level to cause fatalities, Jonathan told The Jakarta Post.

All three fault lines in the province have the potential to cause shallow earthquakes affecting structures at ground level.

The Renun fault runs through the Karo, Dairi Toba Samosir, Pakpak Bharat and Humbang Hasundutan regencies. The Toru line runs through Tapanuli, while the third, the Angkola, is located in the Tapanuli and Mandailing Natal regencies.

Jonathan said all three faults had caused quakes, the first from the Angkola fault in 1892 measuring 7.7 on the Richter scale, the second by the Renun fault in 1936 at 7.2 on the Richter scale and the Toru fault creating two quakes in 1984 and 1987 measuring a magnitude 6.4 and 6.6.

Most recently, the province was affected by the massive offshore earthquake along the major fault at the meeting of the earth’s tectonic plates, which caused the magnitude-9 Aceh earthquake and tsunami and Nias quake in 2004 and last year.

Earthquakes occurred in irregular cycles and active fault lines could produce up to three quakes a century, he said.

In Yogyakarta, there have been three major tremors in less than 150 years, the first in 1867, the second in 1943 and the latest one in May this year.

“If you look at the previous occurrence of earthquakes, then one along the fault lines in North Sumatra is imminent,” Jonathan said. Smaller intensity tremors are frequently being detected along the faults, causing fractures in the earth’s crust, he said.

As Yogyakarta’s experience had shown, a magnitude-6 quake could destroy many flimsy structures.

Jonathan said fractures in the fault line intersecting the tourist destination of Lake Toba also had the potential to deplete water in the lake gradually, although whether this was occurring was still being studied.

An Australian expert, Professor Ray Cas, earlier warned the country faced the prospect of a “super volcano” eruption that would dwarf earlier catastrophes.

Cas, of Monash University’s School of Geosciences, said the world’s biggest super volcano was Lake Toba on Sumatra. Other super volcanoes are found in Italy, South America, the United States and New Zealand.

Cas said Toba last erupted 73,000 years ago in an event so massive that it altered the whole world’s climate.

Jonathan said a massive quake, followed by a tsunami, could also strike the west coast of Sumatra. The Mentawai and Tello island chains would also be affected, he said.

The islands lie immediately above the “mega thrust” subduction zone where the convergence of the Indo-Australian and Eurasian tectonic plates could trigger a powerful 9-magnitude quake, he said.

“The quake duration at the subduction zone is between 100 to 200 years. The Mentawai Islands were hit by a quake in 1833 and Tello island in 1935,” said Jonathan.

This entry was posted on Tuesday, September 12th, 2006 at 8:53 PM and is filed under Earthquake. You can follow any responses to this entry through the RSS 2.0 feed.