Ocean Drilling Scheduled for the Sumatran Subduction Margin – Source of the 2004 Earthquake and Tsunami

An ocean drilling expedition has been scheduled for 2016 offshore Sumatra – this will be the first time this subduction zone margin has been drilled for scientific purposes. The expedition will take place more than 10 years after the 2004 Boxing Day Earthquake and tsunami that ruptured more than 1200 km of the Indonesian-Indian margin, devastating many coastal communities of the Indian Ocean. Since 2004 enormous amounts of new data have been collected imaging the structure and faults beneath the seafloor, including projects led by Tim Henstock and Lisa McNeill in Southampton. Targets for drilling below the seafloor on the margin and sampling the materials that make up the margin and develop into its fault zones, were first proposed in 2006 – after many years of developing these proposals, the margin will finally be drilling in July-September, 2016! Lisa will be one of the Co-Chief Scientists leading the expedition operated by the International Ocean Discovery Program (IODP), along with Brandon Dugan from Rice University in the US. The 2004 earthquake (and the Japan Tohoku-oki earthquake in 2011) both ruptured to much shallower depths than expected, producing very large earthquakes and tsunami. We think this may have something to do with the very thick sediments on the seafloor and that the basal sediments have become unusually strong as a result and more likely to slip during a large earthquake. The materials comprising the Sumatra subduction zone and the sediments entering the system have never been sampled, other than with very shallow cores (maximum ~10 m). But this ocean drilling expedition will for the first time, drill boreholes within the sediments entering the subduction zone, including the layer of sediment that eventually develops into the earthquake-generating fault. We do not know how the sediments evolve as they are physically and chemically altered as the sediment section builds up to 4-5 km thickness before reaching the subduction zone. These physical and chemical changes and the fluids within the sediment pile are critical to earthquake fault behavior. Sampling and measuring the properties of the materials in situ,coupled with extrapolating their properties to greater burial depths using modeling and experimental techniques will be important goals of this project. The drilling expedition will start to investigate how input materials drive shallow earthquake slip and influence the structure of the margin. Ultimately this will help us understand the hazard potential of this margin, and eventually of others with similar material properties.

Follow this link to a piece in The Conversation by Lisa on how deep sea drilling is being used to learn more about earthquakes and tsunami.

Written by Lisa McNeill