Tectonic evolution of strike-slip zones on continental margins and their impact on the development of submarine landslides (Storegga Slide, Northeast Atlantic)

Submarine landslides have affected the mid-Norwegian margin since the Last Glacial Maximum. However, the role of tectonic movements, and most especially fault reactivation, in generating landslides offshore Norway is largely unconstrained. This study uses high-quality three-dimensional seismic and borehole data to understand how landslide development is controlled by faults propagating within the uplifted south Modgunn arch. Variance and structural maps above the south Modgunn arch show that: (1) local scarps of recurrent landslides were formed close to the largest faults, and mainly above strike-slip faults; (2) distinct periods of fault generation were associated with tectonic events, such as the breakup of the northeast Atlantic Ocean, and those events forming the south Modgunn arch; and (3) important fluid-flow features coincide with faults and sill intrusions. In total, 177 faults were analyzed to demonstrate that fault throw values vary from 10 ms to 115 ms two-way traveltime (8 m to 92 m). We propose that the long-term activity of faults in the study area has contributed to fluid migration, weakened post-breakup strata, and controlled the development of submarine slope instability. In particular, strike-slip faults coincide with the locations of several Quaternary landslide scars near the modern seafloor. Similar processes to those documented in Norway may explain the onset of large-scale landslides on other continental margins.