Description: G33A-0852 The convergent continental margin off Central Chile displays one of the steepest forearc reliefs on earth: the distance from coast to the deformation front, i.e. from 0 to more than 5,000 m water depths just spans less than 100 km. The steep slope is characterized by voluminous submarine landslides, large slumps and deeply incised canyons. On February 27, 2010 this area was shaken heavily by one of the largest earthquakes ever recorded. How did this mega-event affect the seafloor morphology? Did it re-shape the submarine landscape? Did it create new slumps and slides on the continental slope? Were pre-existing fault and slide scarps modified? The pre-event geomorphology is well displayed in a detailed bathymetric map based on a compilation of data from more than 10 cruises with German RV Sonne and Meteor, Chilean RV Vidal Gormaz and British RRS James Cook to the area since 1995. In the framework of the "Rapid Response" project SIOSEARCH (Scripps Institution of Oceanography's Survey of the Earthquake and Rupture Offshore Chile) the same area was surveyed immediately after the earthquake by US RV Melville. Very detailed bathymetric maps were compiled from data of the new Kongsberg EM122 multibeam system onboard RV Melville. Both datasets allow for an unprecedented "before" and "after" comparison of the morphology of the part of the continental slope that was hit by the earthquake. Both datasets were carefully processed applying the same algorithms to achieve comparable high-resolution maps. The high data density allowed to create digital terrain models on a grid with cell sizes as small as 50 m down to a water depth of 5000 m. Additional information from the backscatter and acoustic imagery recordings was also taken into account. So far, a thorough inspection and comparison of pre- and post-event morphology revealed surprisingly small changes, however processing and interpretation of the data is still going on.

Description: The Mw 8.8 megathrust earthquake that occurred on 27 February 2010 offshore the Maule region of central Chile triggered a destructive tsunami. Whether the earthquake rupture extended to the shallow part of the plate boundary near the trench remains controversial. The up-dip limit of rupture during large subduction zone earthquakes has important implications for tsunami generation and for the rheological behavior of the sedimentary prism in accretionary margins. However, in general, the slip models derived from tsunami wave modeling and seismological data are poorly constrained by direct seafloor geodetic observations. We difference swath bathymetric data acquired across the trench in 2008, 2011 and 2012 and find ∼3-5 m of uplift of the seafloor landward of the deformation front, at the eastern edge of the trench. Modeling suggests this is compatible with slip extending seaward, at least, to within ∼6 km of the deformation front. After the Mw 9.0 Tohoku-oki earthquake, this result for the Maule earthquake represents only the second time that repeated bathymetric data has been used to detect the deformation following megathrust earthquakes, providing methodological guidelines for this relatively inexpensive way of obtaining seafloor geodetic data across subduction zone.