Earthquake raises up Simeulue island

Syofiardi Bachyul Jb, The Jakarta Post/Padang

The massive earthquake that occurred on Dec. 26, with its epicenter under the island of Simelue in Nanggroe Aceh Darussalam, has elevated the northern part of the island to some 1.3 meters above sea level, an expert says.

While the southern part of the island, according to Danny Hilman Natawidjaya of the Indonesian Institute of Science's (LIPI) Geotechnology Center, is now about 20 centimeters to 50 cms below sea level.

"No changes were noticed in the middle part," he said.

Other areas close to the quake's epicenter, where the Australian and Sumatran tectonic plates meet, have also altered geographically. Some islands in the Andaman and Nicobar islands, have been elevated to two meters to three meters above sea level, which has also expanded their surface area.

Danny disclosed in Padang recently that the coastlines of Meulaboh and Banda Aceh had sunk by about one meter, causing the disappearance of a number of beaches. The island of Nias has also sunk several centimeters below the surface of the sea.

Danny said the phenomena was the result of the displacement of tectonic plates, in this case the Australian plate, which had pressed down on the Sumatran plate, triggering a huge quake and shifting coastlines inland and beneath the sea.

According to Danny, the coastline of the northern part of Simelue island is about 300 meters from where it was previously and coral reefs that had been visible in shallow waters, are now part of the island.

Danny explained that the epicenter of the magnitude 9.0 quake was most likely under the northern part of the island. "The northern part of the island might not have been lifted if that wasn't the case,"he said.

The island will gradually return to how it was before the quake in centuries to come, he said.

Danny said the geographical shifts would pose a hazard for ships sailing in the area. "The area should be remapped as ships could run aground," said Danny, who observed the Simeulue area with a team from the LIPI Geotechnology Center and the California Institute of Technology (Caltech) from a helicopter in mid- January.

According to Danny, areas deemed risky to ships that require remapping stretch from the west coast of Aceh to Simelue and as far as the Andaman and Nicobar islands.

Danny added that similar changes had occurred in the Mentawai Islands, off the west coast of West Sumatra. A magnitude 9.0 earthquake elevated Pagai island in 1833 and the islands of Siberut and Sipora, also located among the Mentawai Islands were elevated after huge quakes occurred in 1600 and 1797, but they eventually receded to their initial state.

Danny has been conducting studies since 1993 with a number of scientists from LIPI and Caltech, among them Professor Kerry Sieh, on the history and possibility of earthquakes on the west coast of Sumatra.

One of their tasks is to study the condition of the coral reefs off the Mentawai Islands.

The team is also installing a number of Global Positioning Systems (GPS) in several locations on the main island of Sumatra and islands off its west coast to monitor the movement of tectonic plates.