Scientists to create history of seismic activity in Indian Ocean region

A joint team of US, Indonesian, Japanese and German researchers are collaborating on a joint study to create a history of seismic activity in the Indian Ocean region.

Washington, May 1 : A joint team of US, Indonesian, Japanese and German researchers are collaborating on a joint study to create a history of seismic activity in the Indian Ocean region.

The Sunda subduction zone, along the western margin of Sumatra and Java in the Indian Ocean region is similar in structure to the Cascadia Subduction Zone along the North American Pacific Coast. It is site of one of the most devastating tsunamis in modern history, the December 26, 2004 tsunami, triggered by an undersea earthquake that cut a swath of destruction across South and South East Asia.

"We hope to create the same kind of history for the Indian Ocean region, which is surprisingly similar to the Cascadia Subduction Zone in structure. If anything, the Indian Ocean is even better suited for this analysis because there is a huge basin between the rivers and the deep ocean that keeps the terrestrial sediments close to land," said Oregon State University marine geologist Chris Goldfinger.

"The region has had many, many earthquakes in its past, yet we know very little about its seismic history because of its remoteness and access issues. Historical records indicate that there were major earthquakes in Padang in 1797 and 1833 in addition to the two more recent quakes, but the evidence beyond that is a little spotty," he said.

The 32-member scientific team, which will also include eight Indonesian scientists from the Agency for Assessment of Application of Technology in Indonesia, will visit the site of the 2004 Indonesian earthquake and its resulting tsunamis, which devastated nearby Banda Aceh and other coastal cities in the Indian Ocean. They also will visit the site of a second major earthquake that struck west of nearby Nias Island in 2005.

The researchers will take a series of 50 piston core samples - about five to six meters in length - from the seafloor, which is about 4,000 to 6,000 meters below the surface, along the west coast of Sumatra.

From those cores, they will look for coarse sediments called "turbidites" that provide evidence of past earthquakes.

Goldfinger said by dating the fine particles through carbon-14 analysis and other methods, it will be possible for them to estimate with a great deal of accuracy when major earthquakes have occurred in the region.

Goldfinger, one of the world's leading experts on Subduction zone earthquakes, has used this technique to recreate the seismic history of the Cascadia Subduction Zone off the coast of the Pacific Northwest, where he has documented 34 major earthquakes during the past 10,000 years.

According to him, at least 19 of those quakes ruptured along the entire length of the subduction zone - requiring an event of magnitude 8.5 or larger.

"When a major offshore earthquake occurs, the disturbance causes mud and sand to begin streaming down the continental margins and into the undersea canyons. Sediments run out onto the abyssal plain. The coarser turbidites stand out distinctly from the fine particulate matter that accumulates on a regular basis between major tectonic events," said Goldfinger.

"Going back further than 10,000 years has been difficult in the Cascadia Subduction Zone because the sea level used to be lower and West Coast rivers emptied directly into offshore canyons. So, it was difficult to distinguish between storms debris and earthquake turbidites," he said.

ANI