International Ocean Discovery Program Expedition 362 Scientific Prospectus

The 2004 Mw 9.2 earthquake and tsunami that struck North Sumatra and the Andaman-Nicobar Islands devastated coastal communities around the Indian Ocean and was the first earthquake to be analyzed by modern techniques. This earthquake and the Tohoku-Oki Mw 9.0 earthquake and tsunami in 2011 showed unexpectedly shallow megathrust slip. In the case of North Sumatra, this shallow slip was focused beneath a distinctive plateau of the accretionary prism. This intriguing seismogenic behavior and forearc structure are not well explained by existing models or by relationships observed at margins where seismogenic slip typically occurs farther landward. The input materials of the North Sumatran subduction zone are a distinctive, thick (up to 4–5 km) sequence of primarily Bengal-Nicobar Fan–related sediments. This sequence shows strong evidence for induration and dewatering and has probably reached the temperatures required for sediment-strengthening diagenetic reactions prior to accretion. The correspondence between the 2004 rupture location and the overlying prism plateau, as well as evidence for a strengthened input section, suggests the input materials are key to driving the distinctive slip behavior and longterm forearc structure. The aim of Expedition 362 is to begin to understand the nature of seismogenesis in North Sumatra through sampling these input materials and assessing their evolution, en route to understanding such processes on related convergent margins. Properties of the incoming section affect the strength of the wedge interior and base, likely promoting the observed plateau development. In turn, properties of deeper input sediment control décollement position and properties, and hence hold the key to shallow coseismic slip. During Expedition 362, two primary, riserless sites (proposed Sites SUMA-11C and SUMA-12A) will be drilled on the oceanic plate to analyze the properties of the input materials. Coring, downhole pressure and temperature measurements, and wireline logging at these sites will constrain sediment deposition rates, diagenesis, thermal and physical properties, and fluid composition. Postexpedition experimental analyses and numerical models will be employed to investigate the mechanical and frictional behavior of the input section sediments/sedimentary rocks as they thicken, accrete, and become involved in plate boundary slip system and prism development. These samples and downhole measurements will augment the internationally collected site survey bathymetric, seismic, and shallow core data that provide the regional geological framework of the margin. Schedule for Expedition 362 Expedition 362 is based partly on Integrated Ocean Drilling Program (IODP) drilling Proposals 837-Full and 837-Add (http://iodp.tamu.edu/scienceops/expeditions/sumatra_seismo genesis.html). Following ranking by the IODP scientific advisory structure, Expedition 362 was scheduled for the R/V JOIDES Resolution, operating under contract with the JOIDES Resolution Science Operator (JRSO). At the time of publication of this Scientific Prospectus, the expedition is scheduled to start in Colombo, Sri Lanka, on 6 August 2016 and to end in Singapore on 6 October 2016 (61 total days). Accounting for 5 days of port call and 7 days of transit, a total of 49 days will be available for the coring and logging program described in this report (for the current schedule, see http://iodp.tamu.edu/scienceops). Additional details about the facilities aboard the JOIDES Resolution can be found at http://iodp.tamu. edu/labs/ship.html.