Oregon State University

College of Earth, Ocean, and Atmospheric Sciences

North Sumatra Expedition

International Ocean Discovery Program to investigate North Sumatra subduction zone for earthquake potential

Marta Torres

Marta Torres

A team of scientists will embark on an International Ocean Discovery Program (IODP) expedition to investigate earthquake and tsunami behavior of the North Sumatra subduction zone – a little-understood stretch of continental margin that was responsible for the December 2004 magnitude >9 earthquake that struck North Sumatra and triggered a deadly tsunami. The team, which includes Professor Marta Torres with the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University, will spend 56 days at sea coring, sampling, and characterizing the sediments, fluids and crustal rocks entering the system to understand its earthquake potential.

Scientists suspect that the amount of fluids trapped within the sediment plays a key role in earthquake generation. Torres will apply her expertise in pore fluid geochemistry to analyze fluids for their composition and migration pathways. Understanding these pathways could explain the margin's unusual structure and morphology and its potential to generate fluids before and after subduction, which may define conditions of earthquake generation.

The sediments offshore North Sumatra are exceptionally thick due to the Bengal-Nicobar submarine fan sediment system that has developed over tens of millions of years from erosion of the Himalayas. This ocean drilling expedition will for the first time drill scientific boreholes within the sediments entering this subduction zone, including the layer of sediment that eventually develops into the earthquake-generating fault.

Scientists know the sediments originated from the land, but still unanswered is how the sediments evolve as they become physically and chemically altered when the sediment section builds up to 4-5 km thickness before reaching the subduction zone. Increased burial depth and temperatures also affect fluids within the sediment pile, which are critical to earthquake fault behavior and to how the sediments accrete onto the continental margin. Ultimately, the team hopes to understand the hazard potential for this margin, and eventually others with similar material properties and margin morphology.

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