The MIST (Multi-frequency Imaging of the Sunda Megathrust) expedition is a research cruise being led by students from the Scripps Institution of Oceanography. The University of California Ship Funds program is graciously providing support for this mission. The cruise will be conducted on board the R/V Roger Revelle and will be sailing from December 2013 to January 2014, with most of the scientific work taking place in the Indian Ocean around Indonesia. The study area is the Sunda trench, which forms part of the convergent boundary between the oceanic Indo-Australian plate and the Eurasian continental plate. The cruise will perform a survey to create high resolution images of the bathymetry and near-surface structure of the seafloor west of the Mentawai islands, off the coast of the larger island of Sumatra. In addition, sediment cores will be collected to investigate the climate of the Indian Ocean stretching back thousands of years.
This area along the trench is of particular interest to geophysicists because the patch of the Sunda megathrust fault that lies underneath it has generated large earthquakes historically, with the last one
taking place in 1833. However, unlike surrounding portions of the fault, no earthquakes have occurred in the Mentawai patch during the past decade. Thus, the Mentawai patch lies in what is called a "seismic gap" along the Sunda megathrust.
Accurate mapping of the Sunda trench over the Mentawai patch, together with smaller fault systems in the vicinity, could be used in a geological interpretation of the forces that shape the area over time, or as input in computer simulations of earthquake and tsunami scenarios. Still, our ultimate goal is to initiate monitoring of changes in the seafloor over this seismic gap, in the hopes of improving the scientific understanding on how subduction zones deform due to megathrust earthquakes.
The area around the Mentawai patch is also of significant interest for paleoclimate studies. It is located at roughly the same latitude as the Seychelles of the western Indian Ocean. There is a large ongoing
debate concerning the influence of the Indonesian Throughflow (ITF) on the Indian Ocean waters. There is considerable evidence that shows that at the Seychelles a signal of ITF influence would be stronger than any other region of the western Indian Ocean, due to the direct westward flow from the South Equatorial Current.
Collection of a number of shallow gravity cores along the western coast of Sumatra would provide an assemblage of fauna similar to existing collections along the Seychelles. This would allow for a very simple intra-basin comparison of thermocline variability and would make for a very convincing argument regarding decadal and longer variability and strength through time. It would also help to delineate the long-term influence of the ITF on the Indian Ocean basin.