Jacob Geersen

The giant 2010 Chile and 2011 Japan earthquakes ruptured well-known plate-boundaries where their occurrence is expected. What took the scientific community by surprise in both cases were large-magnitude (~Mw=7.0) extensional aftershocks that nucleated on upper-plate normal faults above the seismogenic zone. Although these aftershocks seem to relate to the subduction process, little is yet known about their role in the earthquake cycle or the danger that emanates from them. Where the seismogenic zone extends to shallow depth (Cascadia, Makran) similar aftershocks and associated normal-faults would be located offshore within the gas-hydrate stability field. Their sheer existence and possible seismic activation in an area of gashydrates incidentally provokes questions regarding venting of gas-hydrate after megathrust earthquakes or the danger that they pose on seabed infrastructure related to a possible future exploitation of gas-hydrates. There seems no doubt that for a comprehensive assessment of the geo-hazard in a convergent plate margin the understanding of the role of upper-plate normal faults is fundamental, but lacking behind. This project will help closing this gap in knowledge by studying such normal-faults from different accretionary margins using multi-frequency marine acoustic and seismological data combined with tsunami and earthquake magnitude modelling. The output will advance our understanding of the marine-hazard caused by extension in accretionary subduction zones (key aspect in R06), improve hazard assessments and mitigation efforts in areas where active normal-faults are present (relevant for R02) and inform decision making related to possible exploitation of marine gas-hydrates in actively deforming accretionary margins (relevant for R03).