Marine Geomorphology and Gravity Flow Modelling in Transient Pull-Apart Basins of the Offshore Alpine Fault, New Zealand

The offshore component of the dextral strike-slip Alpine Fault has one of highest slip rates on Earth (~27-32 mm/yr). As it passes offshore, the Alpine Fault becomes segmented, with the formation of several rapidly deforming pull-apart basins. Here we focus on the detailed quantification of the 3 northern-most basins, all located <8 km from the Fiordland coastline. High-resolution 30 kHz multibeam bathymetric data and 30 sediment cores are used to determine Late Holocene (<2 ka) sedimentary delivery pathways and processes. A quantitative geomorphic analysis of each basin using ESRI ArcMap version 10.2 and associated spatial analyst tools, reveal huge complexity along the Fiordland continental margin. The margin is shaped largely by Late Pleistocene glacio-marine sedimentary processes, ongoing tectonic deformation, and localized enhanced deposition of Late Holocene gravity flows in nearshore pull-apart basins. Excellent core coverage over the study area allow us to interpret gravity flow types and behaviours. We use these interpretations along with basin geomorphological boundary conditions to model turbidity current flow behaviours.