Funding by German Research Foundation (DFG)

ALASKA: Relating morphological features of the upper plate slopes to the location and extent of the seismogenic zone: Deep seismic and bathymetric studies of the subduction zone of Alaska and a comparing global study.

The seismogenic zone is that part of a subduction zone where the largest earthquakes worldwide nucleate. Recent studies show that 1.) the landward termination of the seismogenic zone at depth coincides with the shelf break at the seafloor and 2.) large faults (so called splay faults) connect the seaward part of the seismogenic zone with the seafloor. The activation of such splay faults during a subduction earthquake might act as extension of the subduction fault, thus enlarging the seismic energy released during the earthquake. Additionally, splay faults, reaching the seafloor, enhance the potential of generating a large tsunami in connection with the subduction earthquake, raising the hazard potential for the coastal regions.Many open questions arise, when dealing with subduction related great earthquakes. Some of them relate to the lateral variability of subduction zones: How do lateral variations of the upper and lower plates along continental margins affect the location and recurrence of great subduction earthquakes? Do subducting bathymetric features, like seamounts, act as nucleation areas which favor earthquake generation or do they rather form barriers for great subduction earthquakes?One contribution to address these open questions is to analyze two unpublished wide-angle seismic profiles off Kodiak Island, Alaska, in combination with the re-processing and re-interpretation of multichannel seismic data. Additionally, bathymetric data of the Alaska margin would provide the link between subsurface structures derived from the interpretation of the seismic data and the seafloor morphology. The proposed datasets are of high quality and meet todays standards.The results concerning the morphological structure in relation with the internal structure of the Alaska subduction zone will be put in a global context. I will compare the accretionary Alaska subduction zone with seismic and bathymetric data of other subduction settings worldwide (e.g. the erosive Java, accretionary Sumatra, South- and Middle-American margins). This might give new insight on the influence of different input into subduction settings (e.g. the sedimentary input, morphology of the incoming plate, like seamounts). Similarities as well as differences between accretionary and erosive subduction zones with the potential to create great (MW > 8) earthquakes might answer some of the above listed open questions, especially regarding the location and length of the seismogenic zone.