From Margin to Menace: the role of structural inheritance in the geohazards distribution in Norway

Formation of the Norwegian rifted margin in the Mesozoic and Early Cenozoic and denudation of adjacent onshore areas resulted in preferential reactivation of regionally important Paleozoic faults and shear zones as indicated by a variety of published geochronological data. Lithospheric-scale necking impacted the later topographic evolution of the present onshore areas, including an escarpment topography and incision pattern that correlates with the seawards taper of the crystalline crust. The density of large, mapped landslides in turn reflects topographic and structural signals and tend to cluster inboard of sharply tapered areas. Margin formation also resulted in the impregnation of crystalline basement by swarms of smaller structures around multiply reactivated structures that made the bedrock prone for coastal erosion as well as onshore slope instability, with apparent maxima in glacially incised topography in areas inboard of sharply tapered margin segments in North- and Mid Norway as well as inboard of parts of the northern North Sea. Offshore, the sharply tapered Møre segment contains stacked submarine slide deposits in an anomaleously short progradational Quaternary wedge, illustrated spectacularly by the Holocene Storegga slide.  An important part of the geohazards distribution onshore and offshore Norway can thus be viewed as long-term responses to the rifting process through an interplay between crustal-scale inheritance, structural reactivation and saturation and mass redistribution by erosion, especially glacial transport. Other rifted margins that evolved by multiphase extension may display similar relationahips between ancient structural templates and the modern distributiion of geohazards.